Adventures in Development

VSTO: Changes to Zoom percentage not persisted

2011-06-12T20:05:00.002+02:00

I have been playing around with VSTO and for some odd reason, my zoom percentage changed to 10% and any subsequent changes to the zoom percentage were not persisted. Using Google's Code Search, I found some examples of how to change these settings in the code-behind:

this.ActiveWindow.View.Type = Word.WdViewType.wdPrintView;
this.ActiveWindow.View.Zoom.Percentage = 100;

But it is still annoying when going into design-mode and having to zoom in again.

One way to fix this is to close Visual Studio, create a copy of the docx file, make the necessary changes and replace the old file.

WCF: Programmatically set dataContractSerializer's maxItemsInObjectGraph value

2011-02-08T19:33:00.000+02:00

When programmtically setting up a WCF Client, one often have to set the dataContractSerializer's maxItemsInObjectGraph parameter (within the serviceBehaviors) to a higher value than the default 65536.

I struggled a bit to find this one on-line, but finally came across a solution on here.

Here's the way to do it:

foreach (OperationDescription operation in myClient.Contract.Operations)
   operation.Behaviors.Find<DataContractSerializerOperationBehavior>().MaxItemsInObjectGraph = 2147483646;

Where the myClient object is an instance of the ServiceClient.

IIS 7 and SSL Error

2010-04-25T08:22:00.003+02:00

If ever faced with the error ssl_error_rx_record_too_long in IIS 7, check to see if you have IIS 6 Compatibility switched on (Control Panel -> Programs and Features -> Turn Windows features on or off -> Internet Information Services -> Web Management Tools -> IIS 6 Management Compatibility).

WPF: Dynamically create a Table

2010-03-29T10:44:00.007+02:00

Being new to WPF, there are a few funnies you'd need to know about before being able to create a simple table with text.

First, one can't simply add a Table within a Grid container. Tables need to be housed within a FlowDocument. One also need a container to display these FlowDocuments. I found the FlowDocumentScrollViewer to be the simplest. Some code to display a blank table:

<FlowDocumentScrollViewer
      VerticalScrollBarVisibility="Disabled"
      HorizontalScrollBarVisibility="Disabled">
   <FlowDocument>
      <Table Name="myTable"></Table>
   </FlowDocument>
</FlowDocumentScrollViewer>

To populate the table programmatically with some basic text one need to follow the next procedure (the code is pretty much self-explanatory):

int cols = 5;
int rows = 10;

for (int c = 0; c < cols; c++)
   myTable.Columns.Add(New TableColumn());

for (int r = 0; r < rows; r++)
{
   TableRow tr = new TableRow();

   for (int c = 0; c < cols; c++)
      tr.Cells.Add(New TableCell(New Paragraph(New Run("Some Text"))));

   TableRowGroup trg = new TableRowGroup();
   trg.Rows.Add(tr);
   myTable.RowGroups.Add(trg);
}

I must say that this approach (a Run within a Paragraph within a TableCell within a Row within a RowGroup) isn't terribly intuitive and the process seems a bit tedious when only trying to create a simple table.

C#: Calling/Overriding Grandparent Base Class Methods

2009-12-10T18:21:00.006+02:00

I use a base class for 99% of my ASP.Net pages, which executes a few operations in the OnInit() method. Here's a simplified version:

public abstract class BasePage : System.Web.UI.Page, IBasePage
{
  protected override void OnInit(EventArgs e)
  {
     // Do stuff
     Method1();
     Method2();
     Method3();

     // Call System.Web.UI.Page.OnInit
     base.OnInit(e);
  }
}

This works great for all my child classes/pages, but there are a few scenario's where I'd only like to call a specific set of methods, as illustrated here:

public class MyPage: BasePage
{
  protected override void OnInit(EventArgs e)
  {
     // Ommit Method2()
     Method1();
     Method3();

     // This calls BasePage.OnInit, which makes
     // redudant calls to Method1() and Method3(),
     // and the undesired call to Method2().
     base.OnInit(e);
  }
}

It is obvious that the last base.OnInit(e) call will have the undesired effect. Being 6:23 PM, after coding all day, my fried brain's initial thought was to bypass the base class' OnInit(e) method and to call the grandparent's OnInit(e) method directly.

An obvious faux pas. Whenever venturing into the "grandparent" or "grandchild" realm (more than one degree of seperation), you're probably going down the wrong path.

The proper and easy approach is merely to move the method calls out to a seperate method, which one overrides in the child class like so:

public abstract class BasePage : System.Web.UI.Page, IBasePage
{
  protected override void OnInit(EventArgs e)
  {
     // Do stuff
     Initialize();

     // Call System.Web.UI.Page.OnInit
     base.OnInit(e);
  }

  protected virtual void Initialize()
  {
     Method1();
     Method2();
     Method3();
  }
}

public class MyPage: BasePage
{
  protected override void Initialize()
  {
     // Do stuff
     Method1();
     Method3();
  }
}

GNU Plot and SVG: Change the terminal size and font

2009-12-07T16:23:00.004+02:00

Again, not really a dev related issue, but I did not find much info online regarding this.

When using gnuplot to create SVG files, one use the set term svg command that sets the following defaults:

gnuplot> set term svg
Terminal type set to 'svg'
Options are 'size 640 480 fixed fname 'Arial' fsize 12 butt '

One can speficy custom parameters to get the desired output:

gnuplot> set term svg size 640,350 fname 'Times New Roman' fsize 10
Terminal type set to 'svg'
Options are 'size 640 350 fixed fname 'Times New Roman' fsize 10 butt '

Type 'DataContract' is not defined

2009-11-23T09:53:00.002+02:00

This error can be resolved by adding a reference to the .net System.Runtime.Serialization assemly and also importing this namespace in the file where applicable.

Also, applies to Type 'DataMember' is not defined.

VB.NET: Check if an event handler has been assigned to a method

2009-11-03T16:50:00.003+02:00

This is how one checks if an event handler (or any delegate handler for that matter) has been assigned to a method.

' Create the delegate
Public Delegate Sub UpdateEvent()
' Create a handler
Public Update As UpdateEvent

' ...
' Rest of the class
' ...

' Check if the event handler has been assigned to
If Not Update Is Nothing Then
 Update()
End If

'SyncLock' operand cannot be of type '' because '' is not a reference type

2009-11-03T14:51:00.003+02:00

Just had this little error in VB.NET:

Error Message: 'SyncLock' operand cannot be of type 'Boolean' because 'Boolean' is not a reference type.
Error ID: BC30582

I tried to change the variable to type Object, but this seems to be converted to Boolean during runtime, which raises the same error.

A clumsy way around this is to simply use a Boolean array of length 1. There must be a better way though, and I'll update this post when I find a better approach.

Yes, I did say vb. Yes, I am ashamed. Client's request.

Update:
Ok here's the deal on using SyncLock or Monitor.Enter (mutex) with value types such as Boolean, Integer, or Double. One is not supposed to lock value types, as they do not have the necessary overhead fields (MethodTablePointer and SyncBlockIndex) to allow a lock to be acquired. One gets around this issue, by creating a reference type, which acts as a flag when the value type is being written to. More on this at the end of Jeffery Richter's article on Safe Thread Synchronization.

An error occurred while reading the app.config file

2009-10-23T15:46:00.005+02:00

I edited my app.config file manually, which did not seem to agree with VS. Even though the XML was valid, I received the message: An error occurred while reading the app.config file. The file might be corrupted or contain invalid XML. Despite this message the code will still run, but its just annoying.

This is a known bug, which I managed to get rid off by removing the project from the solution, restarting Visual Studio and adding the project again.

SQL Server: Automated log file maintenance

2009-10-22T16:31:00.006+02:00

Ok you've all seen it before. You remote desktop onto a client's sql server to upload your app, when your upload fails due to a lack of disk space. Darnit! So you have to reduce the LDF's, which has grown to be several GBs large.

The following little script will reduce all the non-system db's log files. One can also schedule this script as a job that automatically reduces the log files. (Disclaimer: Read-up on the function log files fulfil before simply using this script. I would not recommend running this on critical production systems.)

-- This gets us all on the same page
use [master]

-- Define some variables
declare @statement varchar(2000) 
declare @dbname sysname
declare dbname_cursor cursor for

-- Select all non-system db's
select [name] from master.dbo.sysdatabases where 
  [name] <> 'master' and 
  [name] <> 'model' and 
  [name] <> 'msdb' and 
  [name] <> 'tempdb'

-- Iterate through each db record
open dbname_cursor
fetch next from dbname_cursor into @dbname
while @@fetch_status <> -1
  begin
    select @statement = ''
    select @statement = @statement + 'use ' + @dbname + '; '

    -- Backup db by runcating only (will not reduce physical file size)
    select @statement = @statement + 'backup log ' + @dbname + ' with truncate_only; '

    -- Get the db log file name
    select @statement = @statement + 'declare @log_file varchar(2000); '
    select @statement = @statement + 'select @log_file = [name] from sys.database_files where type_desc = ''LOG''; '

    -- Reduce the physical file size
    select @statement = @statement + 'exec(''dbcc shrinkfile ('' + @log_file + '', 0)''); '    
    exec(@statement)
    fetch next from dbname_cursor into @dbname
  end
close dbname_cursor
deallocate dbname_cursor

g++ 4.3 more strict with declarations

2009-04-29T14:18:00.018+02:00

I've been moving a bunch of old C++ code over to g++ 4.3 and have found that gcc is now more strict on declarations and I often receive these sorts of errors:

error: ‘memset’ was not declared in this scope
error: ‘strncmp’ was not declared in this scope

I'm going to continually update this look-up table, which will explain what to do when receiving any of these errors:

Error	Resolution
error: ‘memset’ was not declared in this scope	Add #include <cstring>
error: ‘strncmp’ was not declared in this scope	Add #include <cstring>

C++: Increasing void pointer position

2009-04-21T22:45:00.005+02:00

I've becoming better friends with c++ today. I don't think this relationship is going anywhere.

Managed to crack this little stupid nut though. If you have a void pointer (dynamic array) you can increase it as follows:

void* ptr;            // Say of type char
(*(char*)ptr) += 100; // Or any integer

Ossim on Ubuntu causes error on missing llampi++

2009-04-20T16:20:00.003+02:00

When compiling Ossim with lam mpi on Ubuntu 9, you might receive this error:

/usr/bin/ld: cannot find -llammpi++

The easiest way to fix this is to ensure liblam4 and openmpi is installed (via the Synaptic Package Manager) and to edit the Makefile.common in the ossim directory ($OSSIM_HOME), changing the MPI_LIB_PATH.

# Open the Makefile.common
gedit $OSSIM_HOME/Makefile.common

# Locate the following line and set its path to /usr/lib/lam/lib
MPI_LIB_PATH         = -L/usr/lib/lam/lib

Compile GDAL with GeoTiff support

2009-04-20T13:11:00.008+02:00

I've been running Ubuntu on my personal machine for a while now and just realized that the gdal synaptic package does not enable support for GeoTiffs. This is where Gentoo has one up, but its not the end of the world. You can 'simply' build GDAL from source with the correct flags.

Here's what I did:
1. Install the Tiff, GeotTiff, Png and OpenJpeg dev packages and their dependencies (libtiff4-dev, libgeotiff-dev, libpng12-dev and libopenjpeg-dev). Also be sure to install g++ and subversion.
2. Fire up a terminal and checkout the GDAL subversion repository anywhere in your home directory:

svn co http://svn.osgeo.org/gdal/trunk/gdal

3. Go into the GDAL directory and run configure:

cd gdal
./configure --with-geotiff=/usr --with-jpeg=/usr --with-libtif=/usr --without-libtool

4. In theory you should be able to run make now, but the configure script missed the geotiff header files directory so I had to set these manually. This is the error I received:

make -C gtiff install-obj
make[2]: Entering directory `/home/andreh/workspace/project-ossim_dev/gdal/frmts/gtiff'
/bin/sh /home/andreh/workspace/project-ossim_dev/gdal/libtool --mode=compile --tag=CXX g++ -g -O2  -Wall  -I/home/andreh/workspace/project-ossim_dev/gdal/port -I/home/andreh/workspace/project-ossim_dev/gdal/gcore -I/home/andreh/workspace/project-ossim_dev/gdal/alg -I/home/andreh/workspace/project-ossim_dev/gdal/ogr -I/home/andreh/workspace/project-ossim_dev/gdal/ogr/ogrsf_frmts   -DOGR_ENABLED -I/home/andreh/workspace/project-ossim_dev/gdal/port -I/usr/lib/include -I -I/include  -c -o ../o/geotiff.lo geotiff.cpp
libtool: compile:  g++ -g -O2 -Wall -I/home/andreh/workspace/project-ossim_dev/gdal/port -I/home/andreh/workspace/project-ossim_dev/gdal/gcore -I/home/andreh/workspace/project-ossim_dev/gdal/alg -I/home/andreh/workspace/project-ossim_dev/gdal/ogr -I/home/andreh/workspace/project-ossim_dev/gdal/ogr/ogrsf_frmts -DOGR_ENABLED -I/home/andreh/workspace/project-ossim_dev/gdal/port -I/usr/lib/include -I -I/include -c geotiff.cpp  -fPIC -DPIC -o ../o/.libs/geotiff.o
geotiff.cpp:34:21: error: xtiffio.h: No such file or directory
geotiff.cpp:35:21: error: geotiff.h: No such file or directory
geotiff.cpp:36:27: error: geo_normalize.h: No such file or directory
geotiff.cpp:37:23: error: geovalues.h: No such file or directory
geotiff.cpp:46: error: 'GTIF' was not declared in this scope
geotiff.cpp:46: error: expected primary-expression before ',' token
geotiff.cpp:46: error: 'GTIFDefn' was not declared in this scope
geotiff.cpp:46: error: expected primary-expression before ')' token
geotiff.cpp:46: error: initializer expression list treated as compound expression
geotiff.cpp:47: error: 'GTIF' was not declared in this scope
geotiff.cpp:47: error: expected primary-expression before ',' token
geotiff.cpp:47: error: expected primary-expression before 'const'
geotiff.cpp:47: error: initializer expression list treated as compound expression
geotiff.cpp: In destructor 'virtual GTiffDataset::~GTiffDataset()':
geotiff.cpp:2249: error: 'XTIFFClose' was not declared in this scope
geotiff.cpp: In member function 'void GTiffDataset::WriteGeoTIFFInfo()':
geotiff.cpp:3336: error: 'TIFFTAG_GEOPIXELSCALE' was not declared in this scope
geotiff.cpp:3346: error: 'TIFFTAG_GEOTIEPOINTS' was not declared in this scope
geotiff.cpp:3363: error: 'TIFFTAG_GEOTRANSMATRIX' was not declared in this scope
geotiff.cpp:3393: error: 'TIFFTAG_GEOTIEPOINTS' was not declared in this scope
geotiff.cpp:3404: error: 'GTIF' was not declared in this scope
geotiff.cpp:3404: error: 'psGTIF' was not declared in this scope
geotiff.cpp:3413: error: 'TIFFTAG_GEOKEYDIRECTORY' was not declared in this scope
geotiff.cpp:3420: error: 'TIFFTAG_GEODOUBLEPARAMS' was not declared in this scope
geotiff.cpp:3422: error: 'TIFFTAG_GEOASCIIPARAMS' was not declared in this scope
geotiff.cpp:3425: error: 'GTIFNew' was not declared in this scope
geotiff.cpp:3428: error: 'GTIFSetFromOGISDefn' cannot be used as a function
geotiff.cpp:3434: error: 'GTRasterTypeGeoKey' was not declared in this scope
geotiff.cpp:3434: error: 'TYPE_SHORT' was not declared in this scope
geotiff.cpp:3435: error: 'RasterPixelIsPoint' was not declared in this scope
geotiff.cpp:3435: error: 'GTIFKeySet' was not declared in this scope
geotiff.cpp:3438: error: 'GTIFWriteKeys' was not declared in this scope
geotiff.cpp:3439: error: 'GTIFFree' was not declared in this scope
geotiff.cpp: In static member function 'static GDALDataset* GTiffDataset::OpenDir(GDALOpenInfo*)':
geotiff.cpp:4285: error: 'XTIFFClose' was not declared in this scope
geotiff.cpp: In member function 'CPLErr GTiffDataset::OpenOffset(TIFF*, GTiffDataset**, toff_t, int, GDALAccess, int)':
geotiff.cpp:4640: error: 'TIFFTAG_GEOPIXELSCALE' was not declared in this scope
geotiff.cpp:4647: error: 'TIFFTAG_GEOTIEPOINTS' was not declared in this scope
geotiff.cpp:4659: error: 'TIFFTAG_GEOTRANSMATRIX' was not declared in this scope
geotiff.cpp:4700: error: 'TIFFTAG_GEOTIEPOINTS' was not declared in this scope
geotiff.cpp:4724: error: 'GTIF' was not declared in this scope
geotiff.cpp:4724: error: 'hGTIF' was not declared in this scope
geotiff.cpp:4725: error: 'GTIFDefn' was not declared in this scope
geotiff.cpp:4725: error: expected `;' before 'sGTIFDefn'
geotiff.cpp:4730: error: 'GTIFNew' was not declared in this scope
geotiff.cpp:4739: error: 'sGTIFDefn' was not declared in this scope
geotiff.cpp:4739: error: 'GTIFGetDefn' was not declared in this scope
geotiff.cpp:4741: error: 'GTIFGetOGISDefn' cannot be used as a function
geotiff.cpp:4748: error: 'GTRasterTypeGeoKey' was not declared in this scope
geotiff.cpp:4749: error: 'GTIFKeyGet' was not declared in this scope
geotiff.cpp:4751: error: 'RasterPixelIsPoint' was not declared in this scope
geotiff.cpp:4757: error: 'GTIFFree' was not declared in this scope
geotiff.cpp: In static member function 'static TIFF* GTiffDataset::CreateLL(const char*, int, int, int, GDALDataType, char**)':
geotiff.cpp:5707: error: 'XTIFFClose' was not declared in this scope
geotiff.cpp: In static member function 'static GDALDataset* GTiffDataset::CreateCopy(const char*, GDALDataset*, int, char**, int (*)(double, const char*, void*), void*)':
geotiff.cpp:6217: error: 'TIFFTAG_GEOPIXELSCALE' was not declared in this scope
geotiff.cpp:6226: error: 'TIFFTAG_GEOTIEPOINTS' was not declared in this scope
geotiff.cpp:6242: error: 'TIFFTAG_GEOTRANSMATRIX' was not declared in this scope
geotiff.cpp:6279: error: 'TIFFTAG_GEOTIEPOINTS' was not declared in this scope
geotiff.cpp:6301: error: 'GTIF' was not declared in this scope
geotiff.cpp:6301: error: 'psGTIF' was not declared in this scope
geotiff.cpp:6303: error: 'GTIFNew' was not declared in this scope
geotiff.cpp:6304: error: 'GTIFSetFromOGISDefn' cannot be used as a function
geotiff.cpp:6310: error: 'GTRasterTypeGeoKey' was not declared in this scope
geotiff.cpp:6310: error: 'TYPE_SHORT' was not declared in this scope
geotiff.cpp:6311: error: 'RasterPixelIsPoint' was not declared in this scope
geotiff.cpp:6311: error: 'GTIFKeySet' was not declared in this scope
geotiff.cpp:6314: error: 'GTIFWriteKeys' was not declared in this scope
geotiff.cpp:6315: error: 'GTIFFree' was not declared in this scope
geotiff.cpp:6325: error: 'XTIFFClose' was not declared in this scope
make[2]: *** [../o/geotiff.lo] Error 1
make[2]: Leaving directory `/home/andreh/workspace/project-ossim_dev/gdal/frmts/gtiff'
make[1]: *** [gtiff-install-obj] Error 2
make[1]: Leaving directory `/home/andreh/workspace/project-ossim_dev/gdal/frmts'
make: *** [frmts-target] Error 2

And this is how to get rid of it:

# open the GDALmake.opt file with an editor
gedit GDALmake.opt

# locate the CPPFLAGS line and add the include path at the end "-I/usr/include/geotiff"
CPPFLAGS    =  -I$(GDAL_ROOT)/port -I/usr/lib/include -I -I/include -I/usr/include/geotiff

5. One can now run make and make install:

make
sudo make install

Limited Linq to Sql

2009-04-02T21:59:00.004+02:00

I've been playing around (ie pulling my hair out) in my spare time over the last few weeks, trying to make Linq more loosely coupled with a UI and to extend its capabilities to allow for many-to-many table updates. I find it completely rediculous how intricate Ms has made all of this. Perhaps I'm missing the plot, but unless you're trying to do some really simple little application that requires little to no flexibility on the DB side of things, STAY AWAY FROM LINQ.

I wrote my own Linq a few years ago, but decided to give Ms Linq a chance and it hasn't really been smooth sailing. The most enjoyable part of the experience was dragging my tables into the dbml window and seeing VS create all the classes for me. The rest is a friggin nightmare.

I'm not about to give up the fight though, but I'm pretty distraught at the moment.

TexnicCenter DDE Commands for Acrobat Reader

2009-03-11T10:47:00.004+02:00

Not really a dev related post, but I had to re-install Vista due to an epic fail on MS's part. My pc went into sleep mode and wrote the files from the C:\ProgramData\Microsoft directory to the C:\ProgramData\Microso~1 dir.

If this ever happens to you, I'm sorry to say you'll have to re-install your OS. I tried everything to get the files back to where they were supposed to be, but it looks like MS tightened security on FS and its impossible to move some of the Crypto files to where they belong. Even if you boot up in Linux...

Anyhow, I have to get latex running again and I'm using TexnicCenter as an editor. I forgot the DDE commands and had to figure it out again. Joy.

Here's the basic setup:

In TexnicCenter, hit Alt+F7 and click on the viewer tab.
In the "View project output" and "Forward search" options, select the "DDE Command" radio button and fill in the following: Command = [DocOpen("%bm.pdf")][FileOpen("%bm.pdf")], Server = acroview, Topic = control
For the "Close document before running Latex" , select DDE with the same settings as above, but change the command to be [DocClose("%bm.pdf")]

One can also fool around with some other commands. Here's the snippet on DDE from the Adobe Interapplication Communication document:

Acrobat Application DDE Messages
This section lists all DDE messages. For complete descriptions of the parameters associated with DDE messages, see the DDE sections of the Acrobat Interapplication Communication Reference.

Application Configuration

AppExit — Exits Acrobat.
AppHide — Iconifies or hides Acrobat.
AppShow — Shows Acrobat.
CloseAllDocs — Closes all open documents.
HideToolbar — Hides the toolbar.
MenuitemExecute — Invokes a menu item, given its language-independent name.
ShowToolbar — Shows the toolbar.

Document Manipulation

DocClose — Closes the file without saving it and without prompting the user to save the document if it has been modified.
DocDeletePages — Deletes a specified range of pages in a document. It cannot delete all pages in a document.
DocInsertPages — Inserts specified pages from one file into another.
DocOpen — Opens a document and adds it to the list of documents known to DDE, allowing it to be manipulated by other DDE messages (for example, FileOpen).
DocReplacePages — Replaces specified pages using pages from another file.
DocSave — Saves the specified file.
DocSaveAs — Saves an open file into a new file, without warning the user if there is a problem saving.
DocSetViewMode — Controls whether bookmarks or thumbnail images are shown in addition to the document content.
FileOpen — Opens and displays a file, making it the current document and bringing it to the front if it is already open.
FileOpenEx — Opens and displays a file, making it the current document and bringing it to the front if it is already open. The file is opened during an idle loop to allow DDE messages to continue flowing during the opening of large documents.

Document Printing

DocPrint — Prints a specified range of pages from a document, without displaying a modal Print dialog box to the user.
FilePrint — Prints all pages in a document, displaying a modal Print dialog box to the user.
FilePrintEx — Prints all pages in a document, displaying a modal Print dialog box to the user. Only PostScript Level 1 operators are used for PostScript printing. Printing is performed during an idle loop to allow DDE messages to continue flowing during the printing of large documents.
FilePrintSilent — Prints all pages in a document, displaying no print dialog box to the user.
FilePrintSilentEx — Prints all pages in a document, displaying no print dialog box to the user. Only PostScript Level 1 operators are used for PostScript printing. Printing is performed during an idle loop to allow DDE messages to continue flowing during the printing of large documents.
FilePrintTo — Prints all pages in a document to a specified printer, using a specified driver and port, displaying a modal Print dialog box to the user.
FilePrintToEx — Prints all pages in a document to a specified printer, using a specified driver and port, displaying a modal Print dialog box to the user. Only PostScript Level 1 operators are used for PostScript printing. Printing is performed during an idle loop to allow DDE messages to continue flowing during the printing of large documents.

View Manipulation

DocGoTo — Goes to the specified page.
DocGoToNameDest — Goes to the specified name destination within the document.
DocPageDown — Scrolls forward through the document by one screen area.
DocPageLeft — Scrolls to the left by a small amount.
DocPageRight — Scrolls to the right by a small amount.
DocPageUp — Scrolls backward through the document by one screen area.
DocScrollTo — Scrolls the view of the current page to a specified location.
DocZoomTo — Sets the zoom for a specified document.

Search-related

DocFind — Finds a string in a specified file.

Python, GDAL: Set JPEG quality values and other att

2008-12-12T12:14:00.004+02:00

Here I shall show how to set the quality values of the JPEG format in GDAL. This post will build upon this previous article which describes how to create a basic JPEG.

It is pretty trivial to set the quality (and other) JPEG values. Here is a list of parameters one can set for the JPEG format. These parameters are simply passed to the CreateCopy() method as a list of options. Here's an example:

# ... Some other code ... #

if (cmp(output_file_ext.lower(),".jpg") == 0 or cmp(output_file_ext.lower(),".jpeg") == 0):
  # Add options
  options = []
  options.append("QUALITY=90")

  jpg_driver = gdal.GetDriverByName("JPEG")

  # Pass options as parameter
  jpg_driver.CreateCopy( output_file, dst_ds, options=options )
  os.remove(output_file_tmp)

Python, GDAL: Adding GeoTiff Meta Data

2008-12-11T13:25:00.007+02:00

I'm pretty much a noob when it comes coordinate systems and projections. I only know the standard GPS coordinates which are in the latitude/longitude (lat/long) format. It turns out that this system is known as the WGS84 (World Geodetic System) format.

The project I'm busy with at the moment, generates GeoTiff images and I only had a raster with the bottom lower left corner coordinates and the pixel sizes in km. It also happened that this is the only information I needed to generate the GeoTiff.

So this is the info I have:

ncols         174
nrows         115
xllcorner     14.97
yllcorner     -34.54
cellsize      0.11

It's just the number of x and y pixels, the lower left corner and the pixel size.

Now we can go ahead and generate the GeoTiff like so:

if __name__ == '__main__':
# Import libs
import numpy, os
from osgeo import osr, gdal

# Set file vars
output_file = "out.tif"

# Create gtif
driver = gdal.GetDriverByName("GTiff")
dst_ds = driver.Create(output_file, 174, 115, 1, gdal.GDT_Byte )
raster = numpy.zeros( (174, 115) )

# top left x, w-e pixel resolution, rotation, top left y, rotation, n-s pixel resolution
dst_ds.SetGeoTransform( [ 14.97, 0.11, 0, -34.54, 0, 0.11 ] )
  
# set the reference info 
srs = osr.SpatialReference()
srs.SetWellKnownGeogCS("WGS84")
dst_ds.SetProjection( srs.ExportToWkt() )

# write the band
dst_ds.GetRasterBand(1).WriteArray(raster)

Easy as pie with GDAL.

Grep and punctuation marks

2008-12-04T09:41:00.002+02:00

I've often tried to use grep to filter search results for locate and several times I've had to search for a string with locate:

locate svn

This search would obviously include all the '.svn' folders too. Trying to get rid with them with

locate svn | grep -v '.svn'

does not work, since grep uses basic regular expressions, and the period mark will simply match any character.

To explicitly indicate the usage of a punctuation mark, one has to put it in brackets. The statement will now look something like:

locate svn | grep -v '[.]svn'

I just scanned through the grep man pages, and everything is explained pretty clearly there. I'd recommend reading the bit on regular expressions.

MySQL and the joys of security

2008-12-03T16:34:00.003+02:00

I've been running my local MySQL server on Gentoo without hassles for a while and recently tried to connect to it from a remote machine. Obviously there was bound to be some issues and here's how I solved them.

When you first try to connect remotely to the machine, you'll be greeted by this lovely message:

# mysql --user=root --password=some_password --host=192.168.0.1 MYDB
ERROR 2003 (HY000): Can't connect to MySQL server on '192.168.0.1' (111)

To get this sucker out of the way, edit your /etc/mysql/my.cnf file and comment the following line:

# bind-address = 127.0.0.1

Note to all the security girls: Your server will now be accessible from any other networked machine. Oooohh nooooo!!

Anyhow, now we try to connect again, and whooopa!! Another error:

mysql --user=root --password=some_password --host=192.168.0.1 MYDB
ERROR 1130 (00000): Host 'remote_pc_hostname' is not allowed to connect to this MySQL server

Ah bite me. Ok, so you have to grant his Lordship permissions to connect to thy server. In order to do that logon to sql on the sql server itself:

# mysql --user=root --password=some_password
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 11
Server version: 5.0.70-log Gentoo Linux mysql-5.0.70-r1

Type 'help;' or '\h' for help. Type '\c' to clear the buffer.

mysql> GRANT ALL ON *.* TO 'root'@'remote_pc_hostname';
Query OK, 0 rows affected (0.00 sec)

Now all should be well in fairyland, but alas. The code securo freaks over at Sun have presented ye with another trial.

# mysql --user=root --password=some_password --host=192.168.0.1 MYDB
ERROR 1045 (28000): Access denied for user 'root'@'remote_pc_hostname' (using password: YES)

Ok I'm taking the fairytale rubbish too far. Here's what you should've done on the sql server in the first place:

# mysql --user=root --password=some_password
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 11
Server version: 5.0.70-log Gentoo Linux mysql-5.0.70-r1

Type 'help;' or '\h' for help. Type '\c' to clear the buffer.

mysql&gt; GRANT ALL ON *.* TO 'root'@'remote_pc_hostname' IDENTIFIED BY 'some_password';
Query OK, 0 rows affected (0.00 sec)

Sheesh! You little girls are wasting my time. Take a que from MS SQL Server.

Creating JPG's and other formats with Python and GDAL

2008-12-03T11:32:00.004+02:00

Ok for some daft reason the driver.Create() method is not supported by all image drivers, but the driver.CreateCopy() is. The main difference being that Create() actually creates the format from scratch whereas CreateCopy() makes a copy of another existing image. I'm sure they have their reasons, but I don't understand why everything isn't created in a generic image type and then converted to the destintation image format through CreateCopy().

Anyhow, this is how I created a JPEG with GDAL. The same approach can be followed for multiple image formats. See this link for a complete list of supported formats.

# Import libs
import numpy, os
from osgeo import osr, gdal

# Set file vars
output_file = "out.jpg"
output_file_root = os.path.splitext(output_file)[0]
output_file_ext = os.path.splitext(output_file)[1]
output_file_tmp = output_file_root + ".tmp"

# Create tmp gtif
driver = gdal.GetDriverByName("GTiff")
dst_ds = driver.Create(output_file_tmp, 512, 512, 1, gdal.GDT_Byte )
raster = numpy.zeros( (512, 512) )
dst_ds.GetRasterBand(1).WriteArray(raster)

# Create jpeg or rename tmp file
if (cmp(output_file_ext.lower(),"jpg" ) == 0 or cmp(output_file_ext.lower(),"jpeg") == 0):
 jpg_driver = gdal.GetDriverByName("JPEG")
 jpg_driver.CreateCopy( output_file, dst_ds, 0 )
 os.remove(output_file_tmp)
else:
 os.rename(output_file_tmp, output_file)

Create a GeoTiff with Python and GDAL

2008-12-03T08:53:00.005+02:00

It looks like the GDAL tutorial on creating GeoTiff's is slightly outdated (2008/05). I received this error with Python 2.5.2, GDAL 1.53 and NumPy 1.0.4:

Traceback (most recent call last):
File "test.py", line 9, in <module>
dst_ds.GetRasterBand(1).WriteArray(raster)
File "/usr/lib/python2.5/site-packages/gdal.py", line 796, in WriteArray

File "usr/lib/python2.5/site-packages/osgeo/gdal_array.py", line 154, in BandWriteArray
AttributeError: dtype

As far as I can tell this occurs because the matrix raster doesn't have the attribute (property) dtype. Something must have changed, but I managed to get it going by using the numpy lib rather than Numeric.

The code that worked for me looks like this:

import numpy
from osgeo import osr, gdal
format = "GTiff"
driver = gdal.GetDriverByName( format )
dst_ds = driver.Create("out.tif", 512, 512, 1, gdal.GDT_Byte )
raster = numpy.zeros( (512, 512) )
dst_ds.GetRasterBand(1).WriteArray(raster)

One can also explicitly state the matrix's data type by adding the dtype attribute:

raster = numpy.zeros( (512, 512), dtype = numpy.uint8)

PHP: move_uploaded_file, Permission denied

2008-11-18T13:00:00.002+02:00

If you ever receive the failed to open stream: Permission denied error in Linux on the move_uploaded_file function, try changing the upload folder's permissions through the chmod command:

chmod 0777 upload_dir

Nesting floating DIV overflow problem

2008-11-17T09:46:00.007+02:00

I had an issue with non-IE browsers where a floating div would oveflow its parent container.

Here's an example:

<div id="Container" style="background-color: Blue; width: 400px; padding: 10px;">
 <div id="Image" style="float: left;">
     <img src="http://www.google.com/images/logo.gif" />
 </div>
 Some text yada yada. Some more text yada dada.
</div>

One can solve this issue by simply adding a div that places a break after the floating div:

<div style="clear: both; font: 1px/1px sans-serif;">&nbsp;</div>

So in the end, it should look something like this:

<div id="Container" style="background-color: Blue; width: 400px; padding: 10px;">
 <div id="Image" style="float: left;">
     <img src="http://www.google.com/images/logo.gif" />
 </div>
 Some text yada yada. Some more text yada dada.
 <div style="clear: both; font: 1px/1px sans-serif;">&nbsp;</div>
</div>

PHP Web Application Root URL

2008-10-28T15:13:00.003+02:00

I wrote this little function to return a PHP applicaiton's root url. It is very quick and dirty, but I thought I'd still share it:

function get_app_root_url()
{
    $app_root_dir_name = getcwd();
    $idx = strripos($app_root_dir_name, '/');
    
    if($idx >= 0)
        $app_root_dir_name = substr($app_root_dir_name, $idx + 1);

    $app_root_url = get_page_url();
    
    $idx = strpos($app_root_url, $app_root_dir_name);
    
    if($idx >= 0)
        $app_root_url = substr($app_root_url, 0, $idx + strlen($app_root_dir_name));
        
    return $app_root_url;
}

// Curtosy of http://www.webcheatsheet.com/PHP/get_current_page_url.php
function get_page_url() 
{
    $page_url = 'http';
    
    if ($_SERVER["HTTPS"] == "on") 
        $page_url .= "s";
    
    $page_url .= "://";
    
    if ($_SERVER["SERVER_PORT"] != "80") 
        $page_url .= $_SERVER["SERVER_NAME"].":".$_SERVER["SERVER_PORT"].$_SERVER["REQUEST_URI"];
    else 
        $page_url .= $_SERVER["SERVER_NAME"].$_SERVER["REQUEST_URI"];
    
    return $page_url;
}

So long Java!

2008-10-24T14:12:00.003+02:00

I've been struggling on and off for over two weeks to get my development environment up and running for Java web apps. I went with the JBoss Seam framework, since it was supposedly lightweight; Eclipse because it had a lot of plugins and seamed to be the most popular free IDE; Tomcat, since its what our web server is running.

In the end I had to ditch Eclipse because it has major issues with plugins cross versions. It's near impossible to get the right jar files and versions for all the Tomcat, Seam and Debugging plugins to play together. So I went with NetBeans, which seemed to be miles simpler to use, but with less functionality and a smaller community.

Even with the simpler NetBeans it was still a mission to get everything working. Finally I was ready to start doing some real coding, but oh my, what a mess!! Perhaps I'm just an idiot, but Seam doesn't have any logical (/www/myproject/...) structure and there's hundreds of XML files all over the shop. Phew... I tried to follow a few tutorials, but I was unable to find a good one. There isn't a single one that just says 1. Here is all the crazy config files, 2. Here is the code, 3. This is how it it all is structured, 4. This is how you deploy... bla bla. Come on people! Keep it simple!

After getting the examples going I read somewhere that I would need JBoss AS in order to run Enterprise Java Beans and it seemed like Seam used EJB for session management or something. Aaargh!!!! The Seam website explicitly states that you can run Seam on Tomcat, but fails to mention that you wouldn't have all the functionalities. What a load of rubbish!! Our web server only runs Apache 2 and Tomcat, so this is a bit of an issue.

I could see that ease of web development in Java is still VERY mush inferior to the likes of Asp.Net or RoR. It's almost impossible for a noob to create a simple website that queries a db with an IDE that supports debugging.

I had a quick look at PHP and it took me two days (which is also far too long for my liking) to get a full dev environment setup with Apache 2, MySql, Eclipse, PDT and Zend. After that my first application was up and running within minutes. PHP is logical, very well documented and has a huge dev community. It seems brilliant!

So that was the final blow to the head for Java. I can't understand why Java is so popular in big enterprises. Well at least for the web side of things. It's like using C++ to run a web app. It simply isn't geared for that purpose. Or perhaps I'm just missing something.

Facelets Support in NetBeans 6.1

2008-10-16T11:04:00.003+02:00

After getting Seam working by manually deploying a .war, I moved onto the next step of integrating Seam into an IDE. Eclipse is a clunky heap of rubbish. I'd say its problem is that it is too flexible. There's a million ways to do one simple thing, but no single way to do one simple thing properly.

After serveral hours wasted on Eclipse, I moved over to NetBeans (6.1). There's a great little tutorial on getting your NetBeans environment setup over at Edem Morny's tech blog. Everything went smoothely, up to the part where one installs Facelets Support, where I get this nasty little message:

Missing required modules for Plugin Facelets Support:
JSP Parser [module org.netbeans.modules.web.jspparser/3 = 200805300101]

This can be avoided by not updating NetBeans. Fortunately there is a bit of a hack to get around this issue:
1. Go to your netbeans-6.1/enterprise5/modules directory
2. Unjar the org-netbeans-modules-web-jspparser.jar file

jar xf org-netbeans-modules-web-jspparser.jar

3. Create a backup of the orignal org-netbeans-modules-web-jspparser.jar just in case.
4. Edit the META-INF/MANIFEST.MF file.
5. Change the OpenIDE-Module-Implementation-Version: to match the verion the facelet is complaining about. In this instance 200805300101.
6. Save the file and jar the whole thing again (by explicitly adding the modified manifest file)

jar cfm org-netbeans-modules-web-jspparser.jar META-INF/MANIFEST.MF org

Manaully clean your Gentoo world file

2008-09-25T17:14:00.004+02:00

I've been in a love-hate relationship with Gentoo for over 3 years now. Luckily there's a lot more love than hate these days. Well 3 years is a long time and it's time to clean this bad boy up...

There's a lot of articles on-line on how to remove cruft and deprecated packages etc. But I struggled to find one that will help you clean up your world file. Being a bit of a quick fix kind of guy, I hammered this little python script together, which will loop through your world file and find the package description for each entry. The script isn't perfect, but it gets the job done for the most part. I still have to manually edit the world file, but at least now I get a description of each entry as I step through the file.

Here's what you need to do:

Log in as root and fire up a text editor:

nano print_world_file_details.py

And paste the following:

import os
import string
import sys

if __name__ == '__main__':
 f_in = open("/var/lib/portage/world")

 lines = f_in.readlines()

 for line in lines:
     index = line.find("/")
     length = len(line) - 1
  
     if(index > 0):
         print ""
         print "--------------------------------------"
         print line[index+1:length]
         print ""
         cmd = "emerge -s " + line[index+1:length] + " | grep -A7 '" + line[:length] + "' "
         os.system(cmd)
      
     sys.stdin.readline()

 f_in.close()

Exit and save (Ctrl+x, Enter). Run the script:

python print_world_file_details.py

Just hit enter after each lookup and manually remove the entry from your world file. Since the script uses grep to filter the ermerge -s results you might get multiple descriptions for some packages. Like dev-java/java-config will list dev-java/java-config-wrapper too. A slight nuisance, but who cares?

Note: It is not considered safe to update your world file manually, so don't mess around if you don't know what you're doing. Please make a backup before editing.

Get JBoss Seam going on Gentoo Linux with Tomcat

2008-09-23T11:21:00.009+02:00

I've been given a web app to do for an open source driven organization. I like the ideology behind open source, but I must say that the complexities involved in just getting started, must be the single biggest hurdle in the adoption of OSS.

Most Java and Linux fanboys might rupture a vain for me saying this, but to get any sort of Java web app going is massive pain in butt. To get Asp.Net going, one merely install visual studio and off you go. You don't even need IIS these days. To get a Java web app (dev environment) going you have to install a web server, an application server, a java framework, an IDE, IDE plugins to support the java framework and perhaps additional frameworks / tools which will allow you to work in a "code-behind" fashion. Then you have to decide on a web frameworks and the choices are endless: Spring MVC, Struts, Seam, JSF, Tapestry, Wicket, Hibernate, Stripes, etc. You can Google until you're blue in the face, but every single framework claims to be the best and all have their own following of groupies. To be honest, it is a big geeky mess!

Unfortunately I don't have the luxury of cleaning up this steaming pile of rubbish, so I'll have to get my hands dirty and figure out what the best solution is through trial and error (very scientific).

My client already has Tomcat running, so luckily I don't have to bother about figuring out which application server is the best. A further requirement is that the web framework should be quite lightweight. It seems as if JBoss' Seam framework isn't too much of a brute, so I'll go with that and probably get burned half-way in.

Even though I detest overcomplicated systems, I've grown quite fond of Gentoo. Once you've mastered this beast, it is quite pleasant to work with. (Perhaps I'll have the same feelings towards Java web apps once I've finished here, but for now it's not looking good.) So I'll run through the steps of getting Seam going on Gentoo.

To start off with, we'll need JDK (or JRE). Login as root, emerge sun-jdk (in my case version 1.6.0.07) and logout. After that we need to get Tomcat.

Note: You can try to get Tomcat going through portage, but you'll end up pulling your hair out, because Seam uses the naming-factory-dbcp.jar, which is not included in the build for some bizarre reason.

cd ~
mkdir applications
cd applications
wget http://apache.mirrors.hoobly.com/tomcat/tomcat-6/v6.0.18/bin/apache-tomcat-6.0.18.tar.gz
tar -xf apache-tomcat-6.0.18.tar.gz

Now let's set the environmental variables needed:

nano ~/.bashrc

and add these lines:

export JRE_HOME=/opt/sun-jdk-1.6.0.07
export TOMCAT_HOME=/home/yourname/applications/apache-tomcat-6.0.18
export CATALINA_HOME=$TOMCAT_HOME
export CATALINA_BASE=$TOMCAT_HOME

Note: You might want to emerge the tomcat-native package, since it will add the Apache Tomcat Native library. I'm not sure if Seam needs this, but I noticed Tomcat having a bit of a fit when it couldn't find it. The message in the $TOMCAT_HOME/logs/catalina.out was "INFO: The APR based Apache Tomcat Native library which allows optimal performance in production environments was not found on the java.library.path"

One can also configure an admin user, but this is not necessarily required. Edit the tomcat-users.xml file like this:

nano $TOMCAT_HOME/conf/tomcat-users.xml

<tomcat-users>
<role rolename="manager">
<user username="root" password="irock" roles="manager">
</user>

One can now start Tomcat:

cd $TOMCAT_HOME/bin
./startup.sh

You should now be able to access Tomcat on http://localhost:8080

Tomcat will display $TOMCAT_HOME/webapps/ROOT/index.html

So we can now follow Seam's Tomcat guide, which I had to modify a bit:

1. Go into the jboss-seam/examples/jpa directory
2. Copy the lib/hsqldb.jar into $TOMCAT_HOME/lib
3. Run ant tomcat6 to build the application
4. Stop Tomcat $TOMCAT_HOME/bin/shutdown.sh
5. Remove previous any exiting deployments: rm -r $TOMCAT_HOME/webapps/jboss-seam-jpa
6. Copy war file: cp dist-tomcat6/jboss-seam-jpa.war $TOMCAT_HOME/webapps
7. Start Tomcat $TOMCAT_HOME/bin/starup.sh
8. Access the app at http://localhost:8080/jboss-seam-jpa

And Bob's you're uncle!

Linq Context.Add Renamded To

2008-09-17T19:34:00.006+02:00

A number of Linq to Sql tutorials online are based on intial "Orcas" (now 3.5) release of the .Net Framework. A number of namechanges were made and I picked one up whilst learning Linq. Here's the error I received:

'System.Data.Linq.Table<Namespace>' does not contain a definition for 'Add' and no extension method
'Add' accepting a first argument of type 'System.Data.Linq.Table<Namespace>' could be found
(are you missing a using directive or an assembly reference?)

The context.Add methods was changed to context.InsertOnUpdate.

Apply themes to Images in Asp.Net

2008-09-10T17:17:00.011+02:00

The Asp.Net Themes approach is somewhat lacking when it comes to images. It is easy enough to switch between CSS and Skin files, but switching between images aren't as trivial. Luckily there is a relatively simple way to do this.

My thinking was to set the image folder dynamically. First, we'll have to figure out what our image path is. Say one use the following structure for your image folders:

App_Themes/Theme1/Images
App_Themes/Theme2/Images
...

The following ImagePath accessor can be used to determine the current theme's image path (I would recommend you to put this in a Base class for this to be accessible to all pages/controls):

public string ImagePath
{
  get
  {
      return string.Format("{0}://{1}{2}/App_Themes/{3}", Request.Url.Scheme, Request.Url.Authority, Request.ApplicationPath, Page.Theme);
  }
}

Now that we know where the currently selected theme's images are, we need to set the path for the controls in the aspx page. This is easy enough if you using normal HTML controls as follows:

<img src='<% Response.Write(ImagePath); %>/Image.jpg' />

But this approach does not work for server controls. If you use the following line, you'll receive an error:

<asp:Image ImageUrl="<% Response.Write(ImagePath); %>/Image.jpg" runat="server" />

Error:
Server tags cannot contain <% ... %> constructs.

One could set the asp:image's ImageUrl in the codebehind, but I find it to be a bit clunky. In order to use the ImagePath in the aspx file, one can use an approach by Dave Reed.

Create a class in the App_Code called CodeExpressionBuilder:

using System;
using System.CodeDom;
using System.Web.Compilation;
using System.Web.UI;

[ExpressionPrefix("Code")]
class CodeExpressionBuilder : ExpressionBuilder
{
  public override object ParseExpression(string expression, Type propertyType, ExpressionBuilderContext context)
    {
      return expression;
    }

    public override CodeExpression GetCodeExpression(BoundPropertyEntry entry, object parsedData, ExpressionBuilderContext context)
    {
      return new CodeSnippetExpression(parsedData.ToString());
    }
}

One can now set the ImageUrl in the aspx file as follows:

<asp:Image ImageUrl='<%$ Code: ImagePath + "/Image.jpg" %>' runat="server" />

AJAX ProgressUpdate issue

2008-08-20T14:53:00.003+02:00

I had an issue with the UpdatePanel and ProgressUpdate AJAX extensions controls in ASP.NET.

The following error occurred in the Javascript:

if (this._dynamicLayout) this.get_element().style.display = 'block';

I solved the problem by moving my ProgressUpdate control out of the UpdatePanel's tags. I guess I was looking for trouble when I did that.

Having the ProgressUpdate within the UpdatePanel work in certain instances, but I also had another UpdatePanel in the same UserControl, so it got a bit hairy.

I'd like to verify this, but as always, the deadline looms.

Constraint cannot be special class 'object'

2008-08-13T21:50:00.005+02:00

I was busy creating a generic method to convert a List to a DataTable when I received the error:

Constraint cannot be special class 'object'

on this statement:

public DataTable ListToDataTable(IList list) where T : Object

Blegh... why would this be? Anyhow, I did a workaround by changing the statement to the following:

public DataTable ListToDataTable(T list) where T : IList

A bit annoying, since now one has to send a List and can't simply pass a List.

Another workaround is to use a blank interface, with the statement as:

public DataTable ListToDataTable(IList list) where T : IBlank

Now one can send List if MyClass 'implements' the IBlank interface.

I'm not really too happy with any of these workarounds. I see no reason why the Object class is "too special" to be used as a generic placeholder.

Oh, and merely for interest sake. Here is the generic List to DataTable converter method:

public DataTable ListToDataTable(List list) where T : IBlank
{
DataTable dataTable = new DataTable();

Type type = typeof(T);
PropertyInfo[] properties = type.GetProperties();

// Create the columns
foreach (PropertyInfo property in properties)
    dataTable.Columns.Add(property.Name, property.PropertyType);

// Populate the rows
foreach (T obj in list)
{
    DataRow newRow = dataTable.NewRow();

    foreach (PropertyInfo property in properties)
        newRow[property.Name] = property.GetValue(obj, null);

    dataTable.Rows.Add(newRow);
}

return dataTable;
}

Python: Multi-dimensional dynamic arrays

2008-07-30T15:40:00.003+02:00

Another very poorly documented topic is how to create dynamic arrays of type array. Every second website will show you how to create static 2D arrays, which is pretty much useless for 90% of the practical applications out there.

I 'solved' it to a degree by creating a list of array items, but this is still not ideal. I would like to use a pure multi-deminsional array of type array.

Here's how I did it:

multi_arr = []

for i in range(some_range):
   arr = array('f') # array of type float
  
   # ... populate arr ...

   multi_arr.append(arr)

Julian Day in Python

2008-07-30T09:48:00.003+02:00

I found very little documentation on obtaining the Juilian day with the time module in Python. So this is how it's done:

import time

print time.strftime("%j")

As easy as that!

Linux: shutdown: you must be root to do that!

2008-07-28T16:21:00.007+02:00

In order to use the console commands shutdown, poweroff, halt or reboot, one has to be a super user. One might see messages such as:

shutdown: you must be root to do that!
poweroff: must be superuser.
reboot: must be superuser.
halt: must be superuser.

In some cases the user can simply be added to the wheel group. This should give the user enough privileges to shut the machine down. A more reliable approach is to make use of Sudo, which was specifically designed to allow ordinary users to execute certain super-user-only commands.

The following section will explain how to setup sudo to allow other users to the machine down through the command line under the Gentoo distro.

Install Sudo
Login as su:

su -

Emerge Sudo:

emerge app-admin/sudo

Configure Sudo
Run visudo:

visudo

Enter the following:

# Runas alias specification
YourUserName  ALL=(root) NOPASSWD: /sbin/reboot
YourUserName  ALL=(root) NOPASSWD: /sbin/halt
YourUserName  ALL=(root) NOPASSWD: /sbin/poweroff
YourUserName  ALL=(root) NOPASSWD: /sbin/shutdown

Replace YourUserName with the user name which requires shutdown privileges.

See this guide on how to create a group which allows all its users to shut the machine down.

Named pipes issue: WaitForConnection hangs around indefinitely

2008-07-13T14:02:00.002+02:00

I recently created an IPC client and server based on the newish NamedPipeServerStream and NamedPipeClientStream classes in .NET 3.x.

It worked great, but when trying to stop the server, the main thread would hang aound waiting for the WaitForConnection() statement to return. I tried to kill the thread in a number of ways, but to no avail.

In the end, I created an easy workaround by doing a "dummy" client connection to the server. This will cause WaitForConnection() method to continue and the thread can then be stopped gracefully.

Named pipes issue: System.UnauthorizedAccessException: Access to the path is denied.

2008-07-11T21:05:00.003+02:00

After yesterday's triumphant discovery I had a nightmare of a day trying to figure out why my client couldn't connect to the server. Time and time again, the following exception was raised:

System.UnauthorizedAccessException: Access to the path is denied.
at System.IO.__Error.WinIOError(Int32 errorCode, String maybeFullPath)
at System.IO.Pipes.NamedPipeClientStream.Connect(Int32 timeout)
at System.IO.Pipes.NamedPipeClientStream.Connect()

And in the debug output window:

A first chance exception of type 'System.UnauthorizedAccessException' occurred in System.Core.dll

My best googling skills couldn't find an answer for this one and I ended up trying to change the permission for the NamedPipeServerStream and venturing down the wrong path by changing the PipeAuditRule and PipeAccessRule settings.

In the end turned out my PipeDirection had to be set to InOut, even though I was only streaming information from the Server, and not receiving information.

Here's the winning line of code:

NamedPipeServerStream Pipe = new NamedPipeServerStream(PipeName, PipeDirection.InOut, 1,
   PipeTransmissionMode.Message, PipeOptions.None);

.NET IPC through Named Pipe Servers

2008-07-10T13:15:00.004+02:00

I've been struggling to get my own IPC server and client going. The work was based on this great post on The Code Project. Even though the article was very useful, I found the code to be a bit clunky.

I restructured a lot of it into very neat client / server structure. During debugging, I stumbled onto this "new" addition in the .Net 3.5 Framework. Named pipes are neatly integrated, so no need for my client and server anymore. Doh!

Oh well, I only lost a day's worth of coding, and at least I can rest assured that this part of my project will be quite stable.

Windows Service uninstall failed

2008-07-08T14:40:00.003+02:00

Whilst developing a Windows Service, an exception occurred. I opted not to debug and when I exited the VS instance the service naturally terminated.

When I got back into the Services MMC, my service was marked as Disabled. When trying to uninstall the service through InstallUtil myservice.exe /u, the following exception was raised:

An exception occurred during the Install phase.
System.ComponentModel.Win32Exception: The specified service has been marked for deletion

This problem is easy enough to solve. Just quit the MMC and uninstall the service again.

Visual Studio editor annoyances

2008-07-08T12:26:00.004+02:00

I have the nasty habit of copying code and then accidentally hitting Crtl+C again without selecting any text. VS clears your current clipboard item and replaces it with the line you're on.

I find this quite annoying, but luckily there's a way to get the previous items in the clipboard back. Just keep hitting Ctrl+Shitf+V to cycle through all the previous items.

UI updates and threading

2008-07-03T14:00:00.008+02:00

I've been working on a small Windows Forms app which has a thread running in the background. This read needs to send info back to the UI during certain intervals. It's a pretty easy problem to solve and there are numerous sources on the web explaining this.

I did come across weird behaviour when my app went into a deadlock. It hanged at the Invoke method in the following code:

// This updates some control safely
protected void UpdateSomeControl()
{
    // Check if an Invoke is required
    if (InvokeRequired)
    {
        // Update the UI through delegation
        Invoke((ThreadStart)delegate()
            {
                // ... Update the UI ...
            });
    }
    else
    {
        // ... Update the UI ...
    }
}

This is upposed to work! So what happened?

Turns out there are two types of calls to modify a control in .Net. The first is a SendMessage and the other PostMessage. Invoke uses SendMessage, which causes the update message to be sent, but hangs around until the message has been processed. BeginInvoke uses PostMessage which is basically a fire-and-and-forget approach; the message is added to the queue and the process goes of doing other work without waiting for it to processed.

So my Invoke was obviously hanging around waiting for the control update to be completed, while the control update was waiting for some other process further back in the queue... at least that's how I understand it.

To solve this issue, simply use BeginInvoke rather than Invoke. I'm sure this fix is not appropriate for all problems, but in my case it did the trick.

For a more detailed explenation, see this CodeProject page.

The infamous "\\computer is not accessible. You might not have permission to use this network" error

2008-06-30T16:41:00.000+02:00

I must have come across this stupid error a dosen times and it is often solved by simply changing the Windows machine's Network ID or by running the Network Connection Wizard thingy in the Control Panel -> Connections page.

This time though, we had a computer playing hardball and was only solved by doing the following (from PChuck's Network):

Download and install the Windows 2003 Server Resource Kit Tools.

Click Start | All Programs | Windows Resource Kit Tools | Command Shell.

Type these three lines, one at a time, at the command prompt. The ntrights
commands are case-sensitive, so type them exactly as shown. Note the "+r" in
the second one and the "-r" in the third one:

net user guest /active:yes
ntrights +r SeNetworkLogonRight -u Guest
ntrights -r SeDenyNetworkLogonRight -u Guest

And that solved our problems. Well for most guys. For some reason my Vista still did not want to connect. I changed my Network ID to be same, and whala! It worked! This is a bit peculiar considering that I was able to connect across different Network ID's on my previous XP machine. I don't have time to double check and validate that now though.

More issues moving over to new system

2008-06-29T22:49:00.001+02:00

Ok so I don't have this dll on my system.

Could not load file or assembly 'System.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The system cannot find the file specified.

Just download and install the ASP.NET 2.0 AJAX Extensions package. Problems solved!

Vista administrator woes

2008-06-29T21:45:00.000+02:00

Ok if you're a Vista user you're undoubtely also sick and tired of being bombarded with security pop-ups, which are aimed at keeping the average user from destroying the system with malware.

So you want to be a real administor? Follow these steps:
First, turn off UAC warnings.
1. Go into Control Panel.
2. Open up User Accounts (in classic view) and User Accounts and Family Safety -> User Accounts (in standard view).
3. Click Turn User Account Control on or off and follow the rest of the instructions.

Ok now you got rid of most of the issues, but Vista still with give you a hard time with Services and applications such as SQL Server and Visual Studio. It still won't think you are a full blown administrator and prompt you with the odd warning. Quite annoying.

Finally, Turn off "Run all administrators in Admin Approval Mode"
1. Open a run window, and type in secpol.msc and hit enter.
2. Expans Local Policies -> Security Options.
3. Scroll down to User Account Control: Run all administrators in Admin Approval Mode and disable the damned thing.
4. Restart and all should be well.

Visual Studio 2005 and IIS 7: Unable to open the Web

2008-06-29T20:57:00.000+02:00

I recently upgraded to a new workstation, which came with Vista Ultra SP1. I tried to open my previous web apps and got this message:

"Unable to open the Web 'http://localhost/...'. The Web server does not appear to have the FrontPage server extensions installed."

A quick google search came up with this article on the MS Knoweldge Base:
http://support.microsoft.com/kb/936857

I followed the instructions and enabled the IIS Metabase and IIS 6 configuration compatibility component. I went back into VS Studio, clicked Reload Project, but no luck.

Next I went into IIS 7's management console. I noticed that the web apps were not added to an application pool yet. Just right-click the folder and choose Convert to Application. Reloaded the project again, and nothing...

Trying to solve the issue, I got a bit side-tracked and sorted out some annoying administrator issues.

I rebooted my system and my web app is working!! Whoop whoop!