Thank you that is exactly what I was looking for.

Thanks,

Matt
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Hi Adam,

I read your portion of this reply.But I am unable to understand this
callback fucntionality.
Can you spare sometime and walkthrough with the piece of code you just
showed as an example.I mean adding comments to the code and the
advantages we receive with callbacks with respect to threads.

Thanks,
Deepak

Deepak,

I am certainly not Adam, but I will give it a go for you:
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}

//Declare the external method
[DllImport("user32.dll")]
private static extern bool SendMessageCallback(
IntPtr hWnd,
uint Msg,
IntPtr wParam,
IntPtr lParam,
SendAsyncProc lpCallback, //Call back delegate used
UIntPtr dwData); //data that the call back will return when the
delegate is called.

//internal delegate used to facilitate the callback. When the
message is
//processed by the window this call back will get called.
private delegate void SendAsyncProc(
IntPtr hwnd,
uint uMsg,
UIntPtr dwData,
IntPtr lResult);

//A simple message that most windows can process
//(its result is typically nothing. The window just process the
message and is done)
//The message does not have to be WM_USER and
//can be any valid Windows message. Adam used
//this message for the sake of simplicity in his
//example.
private const uint WM_USER = 0x400;


private void button1_Click(object sender, EventArgs e)
{
//declare the delegate
SendAsyncProc del = new SendAsyncProc(SendMessage_Callback);

//call the external method, sending the message and returning
immediately.
//The callback will get called when the message is processed.
Use this method
//in a similar fashion as the standard "SendMessage" with the
understanding that the
//message may not be processed immediately. You would need to
provide
//valid values for wParam and lParam; in this case zeros are
allowed with WM_USER
SendMessageCallback(
this.Handle,
WM_USER,
IntPtr.Zero,
IntPtr.Zero,
del,
UIntPtr.Zero);
}

//Method called by the delegate when the call back occurs
private void SendMessage_Callback(
IntPtr hwnd,
uint uMsg,
UIntPtr dwData,
IntPtr lResult)
{
// Here is your callback!
//return;
MessageBox.Show("Test");
}

private void label1_MouseDoubleClick(object sender, MouseEventArgs
e)
{
MessageBox.Show("DOUBLE CLICK");
}
}


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