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 protected override void OnKeyPress(KeyPressEventArgs e)
        {
            if (e.KeyChar == (char)Keys.Enter)
            {
                ...Click ausführen...
                e.Handled = true;
            }
            base.OnKeyPress(e);
        }					

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        private void button_menu_KeyPress(object sender, KeyPressEventArgs e)
        {
            if (e.KeyChar == (char)Keys.Enter)
            { button_menu_Click(this, EventArgs.Empty); }
        }					

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        protected override void  OnKeyPress(KeyPressEventArgs e)
        {
            if (e.KeyChar == (char)Keys.Enter)
            {
                OnClick(e);
            }
            
            base.OnKeyPress(e);
        }