C# Simulate VolumeMute press

Question

I got the following code to simulate volumemute keypress:

    [DllImport("coredll.dll", SetLastError = true)]
    static extern void keybd_event(byte bVk, byte bScan, int dwFlags, int dwExtraInfo);

    byte VK_VOLUME_MUTE = 0xAD;
    const int KEYEVENTF_KEYUP = 0x2;
    const int KEYEVENTF_KEYDOWN = 0x0;
    private void button1_Click(object sender, EventArgs e)
    {
            keybd_event(VK_VOLUME_MUTE, 0, KEYEVENTF_KEYDOWN, 0);
            keybd_event(VK_VOLUME_MUTE, 0, KEYEVENTF_KEYUP, 0);
    }

This code doesnt work. I know there's another way to mute/unmute sound by SendMessageW, but I dont want to use SendMessageW because I use KeyState to detect wheter I need to mute the sound or unmute the sound (if the user wants to unmute the sound and its already unmuted then I dont need to toggle - thats why I need to simulate VolumeMute keypress)

Thanks.

When you say it does not work, do you get an exception out of your p-invoke goodness? — dexter, Jan 23 '11 at 16:32

score 8 · Accepted Answer · answered Jan 23 '11 at 17:29

The first reason it doesn't work is because you use the wrong DLL, coredll.dll is Windows Mobile. In the desktop version of Windows, keybd_event is exported by user32.dll. The second reason it doesn't work is because sending the keystroke isn't good enough. Not quite sure why, this seems to be intercepted before the generic input handler.

You can use WM_APPCOMMAND, it supports a range of commands and APPCOMMAND_VOLUME_MUTE is one of them. It acts as a toggle, turning muting on and off. Make your code look like this:

    private void button1_Click(object sender, EventArgs e) {
        var msg = new Message();
        msg.HWnd = this.Handle;
        msg.Msg = 0x319;              // WM_APPCOMMAND
        msg.WParam = this.Handle;
        msg.LParam = (IntPtr)0x80000; // APPCOMMAND_VOLUME_MUTE
        this.DefWndProc(ref msg);
    }

This code needs to be inside a instance method of the form, note how it uses DefWndProc(). If you want to put it elsewhere then you need to fallback to SendMessage(). The actual window handle doesn't matter, as long as it is a valid toplevel one.

the function u gave me does NOT simulate the keypress. It does mute the sound but not simulatin the keypress. However, your answer was useful, I change from coredll.dll to user32.dll and used my function - it worked. thank you. — Ron, Jan 23 '11 at 17:58
Erm, it mutes the sound. Isn't that the whole point? You might want to consider that on my machine, sending the keystroke doesn't work. Others have observed that problem too, there are several questions about it at the MSDN forums. The code I posted is known to work well. — Hans Passant, Jan 23 '11 at 18:02
It does work, like I mentioned before. But my point is that: I got 2 buttons 1 for mute and 1 for unmute - lets say the current state of sound is Muted. I want to unmute the sound, but with ur solution, no matter which button I will press on - they both do the same... so basicly what I need is to get the state of master volume.... — Ron, Jan 23 '11 at 18:07

C# Simulate VolumeMute press

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