c# - Override DrawItem of ComboBox

Question

I changed the highlight color of various of the controls, and I am planning to make more changes. So I though is better to create my own controls and reuse them instead of making the changed for each and every one of them.

I created a new user control, and inherited from System.Windows.Forms.ComboBox. The problem is I cannot find a way to override onDraw like I would for onClick.

So how I would go and override it? Here is the code I used for each control onDraw event

public void comboMasterUsers_DrawItem(object sender, DrawItemEventArgs e)
    {
        e.DrawBackground();

        Graphics g = e.Graphics;
        Brush brush = ((e.State & DrawItemState.Selected) == DrawItemState.Selected) ?
                      Brushes.LightSeaGreen : new SolidBrush(e.BackColor);

        g.FillRectangle(brush, e.Bounds);
        e.Graphics.DrawString(comboMasterUsers.Items[e.Index].ToString(), e.Font,
                 new SolidBrush(e.ForeColor), e.Bounds, StringFormat.GenericDefault);

        e.DrawFocusRectangle();
    }

Thanks!

Answer 1

Here you go:

public class myCombo : ComboBox
{
    // expose properties as needed
    public Color SelectedBackColor{ get; set; }

    // constructor
    public myCombo()
    {
        DrawItem += new DrawItemEventHandler(DrawCustomMenuItem);
        DrawMode = System.Windows.Forms.DrawMode.OwnerDrawFixed;
        SelectedBackColor= Color.LightSeaGreen;
    }

    protected  void DrawCustomMenuItem(object sender, DrawItemEventArgs e)
    {
        e.DrawBackground();
         // a dropdownlist may initially have no item selected, so skip the highlighting:
        if (e.Index >= 0) 
        {  
          Graphics g = e.Graphics;
          Brush brush = ((e.State & DrawItemState.Selected) == DrawItemState.Selected) ?
                         new SolidBrush(SelectedBackColor) : new SolidBrush(e.BackColor);
          Brush tBrush = new SolidBrush(e.ForeColor);

          g.FillRectangle(brush, e.Bounds);
          e.Graphics.DrawString(this.Items[e.Index].ToString(), e.Font,
                     tBrush, e.Bounds, StringFormat.GenericDefault);
          brush.Dispose();
          tBrush.Dispose();
        }
        e.DrawFocusRectangle();
    }
}

You may consider exposing more Properties as you expand your customziation, so you can change them for each instance when you want to..

Also don't forget to dispose GDI objects you create, like brushes and pens!

Edit: Just noticed that BackColor would hide the original property. Changed it to SelectedBackColor, which actually says what it is!

Edit 2: As Simon noted in the comments, there is a HasFlag method and so as of .Net 4.0 one can also write:

      Brush brush = ((e.State.HasFlag(DrawItemState.Selected) ?

which is a little clearer and shorter.

Edit 3: Actually for drawing onto controls the use of TextRenderer.DrawText is recommended over graphics.DrawString..