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        public bool IsActive = false; 
        ...
        globalKeyboardHook gkh = new globalKeyboardHook();                    

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        private void Form1_Load(object sender, EventArgs e)
        {
            ...
            gkh.HookedKeys.Add(Keys.F1);
            gkh.HookedKeys.Add(Keys.F2);
            gkh.HookedKeys.Add(Keys.F3);
            gkh.HookedKeys.Add(Keys.F4);
            gkh.HookedKeys.Add(Keys.F5);
            gkh.HookedKeys.Add(Keys.F6);
            gkh.HookedKeys.Add(Keys.F7);
            gkh.HookedKeys.Add(Keys.F8);
            gkh.HookedKeys.Add(Keys.F9);
            gkh.HookedKeys.Add(Keys.F10);
            gkh.HookedKeys.Add(Keys.F11);
            gkh.HookedKeys.Add(Keys.F12);
            gkh.KeyDown += new KeyEventHandler(gkh_KeyDown);
            gkh.KeyUp += new KeyEventHandler(gkh_KeyUp);
            ...
        }                    

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        private void button2_Click(object sender, EventArgs e)
        {
            if (string.Equals(button2.Text, "Hotkeys aktivieren"))
            {
                button2.Text = "Hotkeys deaktivieren";
                IsActive = true;
            }
            else
            {
                button2.Text = "Hotkeys aktivieren";
                IsActive = false;
            }
        }                    

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        void gkh_KeyUp(object sender, KeyEventArgs e)
        {
                if (e.KeyCode == Keys.F1 && IsActive)
                {
                    F1.Send();
                    e.Handled = true;
                }
                if (e.KeyCode == Keys.F2)
                {
                    F2.Send();
                    e.Handled = true;
                }
                ... //Geht dann genauso gleich bis F12 weiter
        }