Set hint or watermark or default text for ComboBox without adding it as item

Question

So, I\'m trying to put some text showing up on the ComboBox before it has a selection made by the user.

That text should not be an item, selectable by t

Answer 1

Hint, Cue Banner, Watermark or Default Text for ComboBox

You can set hint for ComboBox without adding to items. To do so, if the ComboBox has DropDown or Simple mode, you can send a CB_SETCUEBANNER message to its inner edit control to set hint. If the combo has DropDownListMode, you can handle WM_PAINT or set it to owner draw to draw hint:

Download

You can clone or download the working example:

• Download zip
• GitHub repository

Code

using System;
using System.Runtime.InteropServices;
using System.Windows.Forms;
public class MyComboBox : ComboBox
{
    public MyComboBox()
    {
        DrawMode = DrawMode.OwnerDrawFixed;
    }
    const int CB_SETCUEBANNER = 0x1703;
    [DllImport("user32.dll", CharSet = CharSet.Auto)]
    static extern int SendMessage(IntPtr hWnd, int msg, int wParam, string lParam);
    string hint;
    public string Hint
    {
        get { return hint; }
        set { hint = value; UpdateHint(); }
    }
    private void UpdateHint()
    {
        if (!this.IsHandleCreated)
            return;
        if (DropDownStyle == ComboBoxStyle.DropDownList)
            this.Invalidate();
        else
            SendMessage(Handle, CB_SETCUEBANNER, 0, Hint);
    }
    protected override void OnHandleCreated(EventArgs e)
    {
        base.OnHandleCreated(e);
        if (!string.IsNullOrEmpty(Hint))
            UpdateHint();
    }
    protected override void OnDrawItem(DrawItemEventArgs e)
    {
        string text = Hint;
        base.OnDrawItem(e);
        if (e.Index > -1)
            text = this.GetItemText(this.Items[e.Index]);
        e.DrawBackground();
        TextRenderer.DrawText(e.Graphics, text, Font,
            e.Bounds, e.ForeColor, TextFormatFlags.TextBoxControl);
    }
}