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Read only ComboBox

, 11 Oct 2004
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How to make ComboBox read only

Introduction

Surprisingly the MS Visual Studio ComboBox doesn’t have such an important property: ReadOnly. After searching on internet for solving this problem and not finding a relevant resolution I decided to add this important property to a new ComboBox control.

Using the code

Create a new derived class from ComboBox:

public class NewComboBox    : System.Windows.Forms.ComboBox

Declare private variables:

private bool readOnly;
private Color tBackColor;
private Color tForeColor;
private ContextMenu cmnuEmpty;
private ComboBoxStyle dropDownStyle = ComboBoxStyle.DropDown;
private Color readOnlyBackColor = SystemColors.Control;
private Color readOnlyForeColor = SystemColors.WindowText;

Set custom context menu to be display when read only:

public ReadOnlyComboBox()
{
  cmnuEmpty = new ContextMenu(); //code this menu for your needs
}

Declare ReadOnly property:

public bool ReadOnly
{
  get 
  {
    return readOnly;
  }
  set
  {
    if(readOnly != value)
    {
      readOnly = value;
      if(value)
      {
        this.ContextMenu = cmnuEmpty;
        base.DropDownStyle = ComboBoxStyle.Simple;
        base.Height = 21;
        this.tBackColor = this.BackColor;
        this.tForeColor = this.ForeColor;
        base.BackColor = this.ReadOnlyBackColor;
        base.ForeColor = this.ReadOnlyForeColor;
      }
      else
      {
        this.ContextMenu = null;
        base.DropDownStyle = dropDownStyle;
        base.BackColor = tBackColor;
        base.ForeColor = tForeColor;
      }
    }
  }
}

Override OnKeyDown and OnKeyPress events to stop editing when readonly:

 
protected override void OnKeyDown(KeyEventArgs e)  
{ 
  if(this.ReadOnly && (
    e.KeyCode == Keys.Up  || 
    e.KeyCode == Keys.Down  ||
    e.KeyCode == Keys.Delete))
    e.Handled = true;
  else
    base.OnKeyDown (e);
}

protected override void OnKeyPress(KeyPressEventArgs e) 
{
    if(this.ReadOnly) 
        e.Handled = true;
    else
        base.OnKeyPress (e);
}

Change the DropDownStyle property to reflect property changes only when not ReadOnly:

new public ComboBoxStyle DropDownStyle
{
  get
  {
    return dropDownStyle;
  }
  set
  {
    if(dropDownStyle != value)
    {
      dropDownStyle = value;
      if(!this.ReadOnly) base.DropDownStyle = value;
    }
  }
}

Add back/fore color properties to reflect changes in ReadOnly property:

public Color ReadOnlyBackColor
{
  get
  {
    return readOnlyBackColor;
  }
  set
  {
    readOnlyBackColor = value;
  }
}
    
public Color ReadOnlyForeColor
{
  get
  {
    return readOnlyForeColor;
  }
  set
  {
    readOnlyForeColor = value;
  }
}

ToDo

Eliminate the white border that appears inside the client area when enable XP styles and BackColor is not default color.

License

This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

A list of licenses authors might use can be found here

About the Author

Dan.A.
Software Developer (Senior)
Romania Romania
No Biography provided

Comments and Discussions

 
GeneralMust also disable mouse paste PinmemberFinishedOnTime26-Feb-07 3:25 
QuestionLatest code? PinmemberChuck_Esterbrook27-Dec-06 13:43 
GeneralKeyPress Event Handler Pinmemberjsteve1712-Dec-06 9:16 
GeneralVery good. Pinmemberjotaele30-Oct-06 23:00 
QuestionHow to remove the white border? Pinmembersick bastard1-Jan-06 21:59 
GeneralAnother approach for a ReadOnly ComboBox PinmemberClaudio Grazioli9-May-05 10:12 
GeneralRe: Another approach for a ReadOnly ComboBox PinmemberChuck_Esterbrook27-Dec-06 12:35 
I tried your version, Claudio, because I liked the idea of swapping in the read only text box. However, it does not work well with a TableFlowLayoutPanel. The extra control (the text box) gets added into its own cell upon "_textBox.Parent = ...". Unless there is a way to fix that problem, the combo needs to work by itself (or be incompatible with layout panels).

GeneralToo bad.... Pinmemberemunews28-Feb-05 2:48 
GeneralReadOnlyComboBox in DropDownList Mode Pinmemberpgolds6-Dec-04 5:21 
GeneralRe: ReadOnlyComboBox in DropDownList Mode Pinmemberpgolds6-Dec-04 7:22 

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