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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

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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 
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 
GeneralRe: ReadOnlyComboBox in DropDownList Mode PinmemberDan Anatoli6-Dec-04 19:30 
GeneralRe: ReadOnlyComboBox in DropDownList Mode Pinmemberpgolds7-Dec-04 4:34 
GeneralOptional solution Pinmemberomacias20-Nov-04 8:43 
GeneralRe: Optional solution PinsussAnonymous21-Nov-04 0:02 
GeneralThank You. Pinmemberpgolds19-Nov-04 9:33 
GeneralRefreshing a DropDownList PinmemberPaco7612-Nov-04 7:31 
GeneralNice. One little remark. PinmemberBoyan Botev19-Oct-04 21:14 
GeneralRMB option cut enabled Pinmemberasela.gunawardena@ifs.lk5-Oct-04 0:03 
GeneralRe: RMB option cut enabled PinmemberDan Anatoli5-Oct-04 19:22 
GeneralRe: RMB option cut enabled PinmemberAsela Gunawardena24-Oct-04 23:56 
GeneralRe: Re: RMB option cut enabled PinmemberAsela Gunawardena24-Oct-04 23:58 
QuestionWhy not just change the DropDownStyle Property? PinsussAnonymous30-May-04 7:11 
AnswerRe: Why not just change the DropDownStyle Property? PinmemberDan Anatoli30-May-04 18:57 
GeneralDropDownList can open, but selection can't be changed. PinmemberHanan Nachmany25-Apr-04 1:35 
GeneralCombobox still recieves F4, PageDown and pageUp PinmemberGuemper17-Mar-04 20:11 
GeneralRe: Combobox still recieves F4, PageDown and pageUp PinmemberDan Anatoli18-Mar-04 18:23 
GeneralRe: Combobox still recieves F4, PageDown and pageUp Pinmemberedokan3-May-04 6:20 
General...and you can cut the text PinmemberMarcuse726-May-04 5:14 
GeneralRe: ...and you can cut the text PinmemberDan Anatoli30-May-04 23:02 
GeneralThat's the hard way... PinmemberRay Hayes12-Mar-04 4:02 
GeneralRe: That's the hard way... PinmemberDan Anatoli14-Mar-04 18:50 
GeneralThe easiest way.. Pinmemberyltsa25-Mar-05 21:28 
GeneralRe: That's the hard way... PinmemberSystem.Object21-Apr-06 9:29 
QuestionHOW to add this NewComboBox to the form? PinmemberNappo2310-Mar-04 8:21 
AnswerRe: HOW to add this NewComboBox to the form? PinmemberDan Anatoli10-Mar-04 19:48 
GeneralCombox the worst control PinmemberElNoNo10-Mar-04 3:44 
GeneralRe: Combox the worst control PinmemberRoger J10-Mar-04 3:52 
GeneralRe: Combox the worst control PinmemberSebCode11-Oct-04 3:44 
QuestionDropDownList? PinsitebuilderUwe Keim9-Mar-04 6:31 
AnswerRe: DropDownList? PinmemberDan Anatoli9-Mar-04 18:50 
GeneralRe: DropDownList? Pinmemberstringali6911-Mar-04 5:13 
GeneralRe: DropDownList? PinmemberDan Anatoli11-Mar-04 18:46 
GeneralRe: DropDownList? PinsussAnonymous15-Aug-04 21:09 
GeneralRe: DropDownList? PinmemberDan Anatoli16-Aug-04 0:52 

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