Window Minimize / Maximize Event (C# winforms)

Aug 13, 2012 One-minute read

C Sharp • dotnet • Windows Forms • Win32 API • P/Invoke

If you are working in C# winforms and need to respond to window minimize and maximize events, it seems that winforms does not provide native event handlers. Such a feat is still very much possible through hooking into the Windows API.

The exact message you need to catch is WM_SYSCOMMAND and look for the SC_* messages:

SC_CLOSE 0xF060
SC_MAXIMIZE 0xF030
SC_MINIMIZE 0xF020
SC_RESTORE 0xF120

There are indeed more messages. Check the above link for a full list. Now for some sample code:

protected override void WndProc(ref Message m)
{
    base.WndProc(ref m);
    if (m.Msg == 0x0112) // WM_SYSCOMMAND
    {
        // SC_MAXIMIZE and SC_MINIMIZE
        if (m.WParam == new IntPtr(0xF030) || m.WParam == new IntPtr(0xF020))
        {
            // Event fired! Handle it here
        }
    }
}