7.5 How can I catch keyboard messages on a application-wide basis? |
You can implement the IMessageFilter interface in your main form. This amounts to adding an override for PreFilterMessage, and looking for the particular message you need to catch. Here are code snippets that catch an escape key on a keydown. You can download a sample project(C#, VB). In the sample, there are two forms, with several controls. You'll notice that no matter what form or control has input focus, the escape key is caught in the PreFilterMessage override. |
| [C#]
|
| public class MyMainForm : System.Windows.Forms.Form, IMessageFilter
|
| {
|
| const int WM_KEYDOWN = 0x100;
|
| const int WM_KEYUP = 0x101;
|
|
|
| public bool PreFilterMessage(ref Message m)
|
| {
|
| Keys keyCode = (Keys)(int)m.WParam & Keys.KeyCode;
|
| if(m.Msg == WM_KEYDOWN && keyCode == Keys.Escape)
|
| {
|
| Console.WriteLine("Ignoring Escape...");
|
| return true;
|
| }
|
| return false;
|
| }
|
| ....
|
| ....
|
| ....
|
| private void MyMainForm_Load(object sender, System.EventArgs e)
|
| {
|
| Application.AddMessageFilter(this);
|
| }
|
| }
|
|
|
| [VB.NET]
|
| Public Class MyMainForm
|
| Inherits System.Windows.Forms.Form
|
| Implements IMessageFilter
|
|
|
| Private WM_KEYDOWN As Integer = &H100
|
| Private WM_KEYUP As Integer = &H101
|
|
|
| Public Function PreFilterMessage(ByRef m As Message) As Boolean
|
| Dim keyCode As Keys = CType(CInt(m.WParam), Keys) And Keys.KeyCode
|
| If m.Msg = WM_KEYDOWN And keyCode = Keys.Escape Then
|
| Console.WriteLine("Ignoring Escape...")
|
| Return True
|
| End If
|
| Return False
|
| End Function 'PreFilterMessage
|
| ....
|
| ....
|
| ....
|
| Private Sub MyMainForm_Load(sender As Object, e As System.EventArgs)
|
| Application.AddMessageFilter(Me)
|
| End Sub 'MyMainForm_Load
|
| End Class 'MyMainForm |
|