C# Tips

1.How to Write debug string in C# ?

Using System.Diagnostics.Debug.Writeline() fn, we can write the debug string

2.How do we play default window sounds in C# ?
in .NET 2.0,

System.Media namespace is available. To play for example the classical beep sound, you could use the following code:

System.Media.SystemSounds.Beep.Play();
Similarly, you could play the “Question” sound with this code:
System.Media.SystemSounds.Question.Play();
The System.Media namespace is defined in System.dll, so there are no new DLLs you would need to add to your project’s references to use the above code.
3.What does the /target: command line option do in the C# compiler?
All the /target: options except module create .NET assemblies. Depending on the option, the compiler adds metadata for the operating system to use when loading the portable executable (PE) file and for the runtime to use in executing the contained assembly or module.
module creates a module. The metadata in the PE does not include a manifest. Module/s + manifest make an assembly - the smallest unit of deployment. Without the metadata in the manifest, there is little the runtime can do with a module.
library creates an assembly without an entry point, by setting the EntryPointToken of the PE's CLR header to 0. If you look at the IL, it does not contain the .entrypoint clause. The runtime cannot start an application if the assembly does not have an entry point.
exe creates an assembly with an entry point, but sets the Subsystem field of the PE header to 3 (Image runs in the Windows character subsystem - see the _IMAGE_OPTIONAL_HEADER structure in winnt.h). If you ILDASM the PE, you will see this as .subsystem 0x0003. The OS launches this as a console app.
winexe sets the Subsystem field to 2. (Image runs in the Windows GUI subsystem). The OS launches this as a GUI app.


4.What is the difference between const and static readonly?
The difference is that the value of a static readonly field is set at run time, and can thus be modified by the containing class, whereas the value of a const field is set to a compile time constant.
In the static readonly case, the containing class is allowed to modify it only
in the variable declaration (through a variable initializer)
in the static constructor (instance constructors, if it's not static)
static readonly is typically used if the type of the field is not allowed in a const declaration, or when the value is not known at compile time.
Instance readonly fields are also allowed.
Remember that for reference types, in both cases (static and instance) the readonly modifier only prevents you from assigning a new reference to the field. It specifically does not make immutable the object pointed to by the reference.
class Program
{
public static readonly Test test = new Test();
static void Main(string[] args)
{
test.Name = "Program";
test = new Test(); // Error: A static readonly field cannot be assigned to (except in a static constructor or a variable initializer)
}
}
class Test
{
public string Name;
}
On the other hand, if Test were a value type, then assignment to test.Name would be an error.

5.How do I get and set Environment variables?
Use the System.Environment class.Specifically the GetEnvironmentVariable and SetEnvironmentVariable methods.Admitedly, this is not a question specific to C#, but it is one I have seen enough C# programmers ask, and the ability to set environment variables is new to the Whidbey release, as is the EnvironmentVariableTarget enumeration which lets you separately specify process, machine, and user.
Brad Abrams blogged on this way back at the start of this year, and followed up with a solution for pre-Whidbey users.


6.Preprocess Win32 Messages through Windows Forms
In the unmanaged world, it was quite common to intercept Win32 messages as they were plucked off the message queue. In that rare case in which you wish to do so from a managed Windows Forms application, your first step is to build a helper class which implements the IMessageFilter interface. The sole method, PreFilterMessage(), allows you to get at the underlying message ID, as well as the raw WPARAM and LPARAM data. By way of a simple example:
public class MyMessageFilter : IMessageFilter
{
public bool PreFilterMessage(ref Message m)
{
// Intercept the left mouse button down message.
if (m.Msg == 513)
{
MessageBox.Show("WM_LBUTTONDOWN is: " + m.Msg);
return true;
}
return false;
}
}
At this point you must register your helper class with the Application type:
public class mainForm : System.Windows.Forms.Form
{
private MyMessageFilter msgFliter = new MyMessageFilter();

public mainForm()
{
// Register message filter.
Application.AddMessageFilter(msgFliter);
}
…
}
At this point, your custom filter will be automatically consulted before the message makes its way to the registered event hander. Removing the filter can be accomplished using the (aptly named) static Application.RemoveMessageFilter() method.


7.Be aware of Wincv.exe :


When you install the .NET SDK / VS.NET, you are provided with numerous stand alone programming tools, one of which is named wincv.exe (Windows Class Viewer). Many developers are unaware of wincv.exe, as it is buried away under the C:\Program Files\Microsoft Visual Studio .NET 2003\SDK\v1.1\Bin subdirectory (by default).
This tool allows you to type in the name of a given type in the base class libraries and view the C# definition of the type. Mind you, wincv.exe will not show you the implementation logic, but you will be provided with a clean snapshot of the member definitions.


8.What is the equivalent to regsvr32 in .NET?
Where you once used Regsvr32 on unmanaged COM libraries, you will now use Regasm on managed .NET libraries.
“Regsvr32 is the command-line tool that registers .dll files as command components in the registry“
“Regasm.exe, the Assembly Registration tool that comes with the .NET SDK, reads the metadata within an assembly and adds the necessary entries to the registry, which allows COM clients to create .NET Framework classes transparently. Once a class is registered, any COM client can use it as though the class were a COM class. The class is registered only once, when the assembly is installed. Instances of classes within the assembly cannot be created from COM until they are actually registered.“ If you want to register an assembly programmatically, see the RegistrationServices class and ComRegisterFunctionAttribute