C#: Calling/Overriding Grandparent Base Class Methods

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

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

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

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

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

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

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

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

C++: Increasing void pointer position

I became better friends with C++ today, but somehow 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++

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

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-libtiff=/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

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

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:

1. In TexnicCenter, hit Alt+F7 and click on the viewer tab.
2. 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
3. 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.