Capturing a key without focusing the window

Question

I have a application that always checks if a key like F12 is pressed. It doesn't need to have in focus of my main window of my app. I tried this code:

public int a = 1;
    // DLL libraries used to manage hotkeys
    [DllImport("user32.dll")]
    public static extern bool RegisterHotKey(IntPtr hWnd, int id, int fsModifiers, int vlc);
    [DllImport("user32.dll")]
    public static extern bool UnregisterHotKey(IntPtr hWnd, int id);

    const int MYACTION_HOTKEY_ID = 1;

    public Form1()
    {
        InitializeComponent();
        // Modifier keys codes: Alt = 1, Ctrl = 2, Shift = 4, Win = 8
        // Compute the addition of each combination of the keys you want to be pressed
        // ALT+CTRL = 1 + 2 = 3 , CTRL+SHIFT = 2 + 4 = 6...
        RegisterHotKey(this.Handle, MYACTION_HOTKEY_ID, 0, (int) Keys.F12);
    }

    protected override void WndProc(ref Message m)
    {
        if (m.Msg == 0x0312 && m.WParam.ToInt32() == MYACTION_HOTKEY_ID)
        {

            a++;
            MessageBox.Show(a.ToString());
        }
        base.WndProc(ref m);
    }

I put 0 to this line RegisterHotKey(this.Handle, MYACTION_HOTKEY_ID, 0, (int) Keys.F12); so that only if F12 is pressed it will capture.

But it didn't work. How can I solve this?

Here I couldn't understand some lines like:

const int MYACTION_HOTKEY_ID = 1;
m.Msg == 0x0312 && m.WParam.ToInt32() == MYACTION_HOTKEY_ID
base.WndProc(ref m);

Can anyone help me to understand these lines?

Answer 1

Your code has no wrong . But it doesn't work here because the F12 key is reserved you may try with another key like F10, F11 etc .