class myFilter: 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.Shift) {
 
            }
            if (m.Msg == WM_KEYUP && keyCode == Keys.Shift) {
 
            }
 
 
            //nachricht wird an weitere Filter weitergereicht
            return false;
        }
 
    }