How to Capture the Back Button

Thomas Wells

Many mice have a back button. Many applications implement a goback kind of function, mostly browsers. I'd like to capture a mouse back button so I can offer a similar functionality. Any idea how to tell if the mouse "back" button has been pressed?

Dave Kreskowiak

Well, you'd have to override your Form's WndProc and check for two messages. m.Msg 523 is WM_XBUTTONDOWN and 524 is WM_XBUTTONUP. This is, hopefully obvious, the pressing and releasing of any of the extra buttons on the mouse. When receiving either of these messages, look at the high-order word in the m.WParam property of the message. This will tell you which mouse "extra" button was pressed/released.

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2006, 2007, 2008

Thomas Wells

I had considered intercepting the xbutton messages but the value of a button is programmable on most mice isn't it? Doesn't that mean that some other message is being sent which means "Back". Coding a specific mouse button would not use a mouse's programmed setting.

Thomas Wells

I've gotten a bit closer. It looks like what I want is a virtual key, VK_BROWSER_BACK. It is also recognized as a key modifier, Keys.BrowserBack. These don't seem to come through in the OnKeyDown override. I've seen code samples that implement IMessageFilter.

Public Class Form2
Implements IMessageFilter

Public Function PreFilterMessage(ByRef m As System.Windows.Forms.Message) As Boolean \_
      Implements System.Windows.Forms.IMessageFilter.PreFilterMessage
    Dim keyCode As Keys = CType(m.WParam.ToInt32(), Keys) And Keys.KeyCode
    If keyCode = Keys.BrowserBack Then
        Console.WriteLine("I found it")
    End If
End Function

End Class

Of course this doesn't work either. It never finds Keys.BrowserBack. I've seen m.WParam have values 65568(10020h) & 65536(10000h) when I press my browser back key (xButton on the mouse). Any ideas?

modified on Monday, March 9, 2009 2:25 PM

Dave Kreskowiak · modified on Monday, March 9, 2009 2:25 PM

The only thing I can suggest would be the documentation on WM+_XBUTTONDOWN[^]. Since the values in the Params are the result of the combining of smaller fields into a 32-bit value, you have to do some math to figure out what each of these fields means.

A guide to posting questions on CodeProject[^]
Dave Kreskowiak Microsoft MVP Visual Developer - Visual Basic
2006, 2007, 2008