Question

How to hide DropDownList in ComboBox?

I want use ComboBox only for displaying text.
This control look nice, for me is better than TextBox plus Button.
So control must be enabled, but without any items.
When user click arrow (or alt + down key) DropDownList should’n show, because ill select value from custom DataGridView in order to fill back text in ComboBox.

Edit. Alternative solution is set DropDownHeight to 1, with show only 1 pixel line after clicking control.

Edit. Real solution. Answer below

Answer 1

You can intercept the messages that cause the box to drop-down, in a subclass. The following snippet defines a control NoDropDownBox, that ignores the mouse clicks that result in a drop-down of the combo box:

public class NoDropDownBox : ComboBox
{
    public override bool PreProcessMessage(ref Message msg)
    {
        int WM_SYSKEYDOWN = 0x104;

        bool handled = false;

        if (msg.Msg == WM_SYSKEYDOWN)
        {
            Keys keyCode = (Keys)msg.WParam & Keys.KeyCode;

            switch (keyCode)
            {
                case Keys.Down:
                    handled = true;
                    break;
            }
        }

        if(false==handled)
            handled = base.PreProcessMessage(ref msg);

        return handled;
    }

    protected override void WndProc(ref Message m)
    {            
        switch(m.Msg)
        {
            case 0x201:
            case 0x203:
                break;

            default:
                base.WndProc(ref m);
                break;
        }
    }
}