Article information
Article relates to	RadComboBox for WinForms
Created by	Georgi Stoyanov, Telerik
Last modified	May 21, 2008
Last modified by	Georgi Stoyanov, Telerik

HOW-TO
Implement checkbox items in RadComboBox

SOLUTION
To implement checkbox items in RadComboBox you'll have to extend the RadComboBoxItem class and change the structure of the combobox item.

1. First, in CreateChildElements() you should set the left margin of the TextPrimitive to make enough room to checkbox (otherwise the checkbox will appear over the text).
2. Create new instance of RadCheckBoxElement and set its StretchHorizontally and StretchVertiaclly properties to false (these properties are available since Q3 2007 release).
3. Then add the newly created RadCheckBoxElement.
4. You can further enhance the custom combobox item by adding mouse and keyboard events to set up your custom logic:
    
   

   public class RadCustomComboBoxItem : RadComboBoxItem

   {

   public RadCustomComboBoxItem(string text)

   : base(text)

   {

   }

   public RadCustomComboBoxItem(string text, MouseEventHandler OnClick)

   : base(text, OnClick)

   {

   }

   private RadCheckBoxElement chBox;

   protected override void CreateChildElements()

   {

   base.CreateChildElements();

   this.Children[2].Children[1].Margin = new Padding(15, 0, 0, 0);

   this.chBox = new RadCheckBoxElement();

   chBox.StretchHorizontally = false;

   chBox.StretchVertically = false;

   this.Children.Add(chBox);

   }

   }

Here's a screenshot of the form with RadComboBox using custom items with checkboxes:



A small C# sample project is also attached to show how this works. 

Another approach could be to use the RadItemCollection.ItemsChanged event. The event handler should be attached before adding the items in the Items collection. The code of the event handler would check the operation if it is Telerik.WinControls.ItemsChangeOperation.Inserted and would do the same as has been mentioned in the CreateChildElements() method.

Also, if the case is with a RadComboBox bound to a data source, the RadComboBox.ItemDataBound event could be used. In the event handler for this event, the current instance of the RadComboBoxItem is passed by the DataBoundItem property of ItemDataBoundArguments. After obtaining the item, the rest of the code is same as in the other cases.