WndProc: How to get window messages when form is minimized
To communicate with a certain service, I have to override the WindProc
. and receive window messages.
However, when the form is minimized, I get no longer any message. I know that it has to be like that, but is there a workaround for this? I don't want to have a hidden form whi开发者_StackOverflow社区ch stays always open...
I've also needed to solve a similar problem recently. Abel's answer set me on the right direction. Here is a complete example of how I did it, by changing a normal window into a message-only window:
class MessageWindow : Form {
[DllImport("user32.dll")]
static extern IntPtr SetParent(IntPtr hWndChild, IntPtr hWndNewParent);
public MessageWindow() {
var accessHandle = this.Handle;
}
protected override void OnHandleCreated(EventArgs e) {
base.OnHandleCreated(e);
ChangeToMessageOnlyWindow();
}
private void ChangeToMessageOnlyWindow() {
IntPtr HWND_MESSAGE = new IntPtr(-3);
SetParent(this.Handle, HWND_MESSAGE);
}
protected override void WndProc(ref Message m) {
// respond to messages here
}
}
Pay attention to the constructor: I've found that I need to access the Handle property or otherwise the OnHandleCreated method won't get called. Not sure of the reason, perhaps someone can explain why.
I believe my sample code also would answer a related question: How do I create a message-only window from windows forms?
If you want to receive window messages, but don't want to show a form for receiving them, you can use a message-only window, which is never displayed. If you use that, the actual C# Form you use for interacting with the user is no longer needed to also receive the messages from your window service.
Here's more on the subject as MSDN. A warning though, it requires quite a bit of playing around with the Window API, because a message-only window is not directly supported by .NET.
You can try NativeWindow
to receive messages (VB code, sorry):
Imports System.Windows.Forms
Public Class MyClass: Inherits NativeWindow
Private piFormHandle As Integer = 0
Sub New()
Me.CreateHandle(New CreateParams)
piFormHandle = CInt(Me.Handle)
End Sub
Protected Overrides Sub WndProc(ByRef m As System.Windows.Forms.Message)
Select Case (m.Msg)
Case MyMessage
End Select
MyBase.WndProc(m)
End Sub
End Class
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