Named parts in wpf control template

When a template author in WPF tries to modify the look of the control , it is the controltemplate of the control that get changed.

To retain core functionality of a control , the template looks for some named elements with fixed names.If it is not found in the template , the core functionality of the control won’t work.

Eg.

Lets say we are creating a textbox which has an image as below.

 <TextBox Width="150" Height="80">  
               <TextBox.Template>  
                 <ControlTemplate>  
                   <StackPanel>  
                         <Image Source="tab_active.png"/>  
                   </StackPanel>  
                 </ControlTemplate>  
               </TextBox.Template>  
  </TextBox>   

This code will get executed but you can’t type in anything which is one of the core functionality of a textbox.It is because the template of the textbox assumes a name “PART_ContentHost” to be present in the template so that it can apply the core functionality of text box to it. The “PART_ContentHost” named part for a textbox can be named to a ScrollViewer or any control derived from AdornerDecorator (Decorator,Border etc…). Lets modify out textbox with this named part,

 <TextBox Width="150" Height="80">  
               <TextBox.Template>  
                 <ControlTemplate>  
                   <StackPanel>  
                      <Image Source="tab_active.png"/>  
                      <ScrollViewer Name="PART_ContentHost" />  
                   </StackPanel>  
                 </ControlTemplate>  
               </TextBox.Template>  
  </TextBox>   

A way to find these named parts is digging into the definition of the control or its base.The TemplatePart attribute contains the named parts of the control.

E.g.

  [TemplatePart(Name = "PART_ContentHost", Type = typeof(FrameworkElement))]

    [Localizability(LocalizationCategory.Text)]

    public abstract class TextBoxBase : Control

for combobox ....
 

  [Localizability(LocalizationCategory.ComboBox)]

    [TemplatePart(Name = "PART_EditableTextBox", Type = typeof(TextBox))]

    [TemplatePart(Name = "PART_Popup", Type = typeof(Popup))]

    [StyleTypedProperty(Property = "ItemContainerStyle", StyleTargetType = typeof(ComboBoxItem))]

    public class ComboBox : Selector

Hope this helps.