Inheriting ComboBox in WPF using C#

I am deriving from Combobox to add some additional functionality, such as a checkbox.

The issue is, even with a simple implementation the Items.Add method does not work.

For example, here is the XAML:

<Style TargetType="{x:Type local:CustomControl1}">
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="{x:Type local:CustomControl1}">
                <ComboBox>
                </ComboBox>
          开发者_StackOverflow中文版  </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>

The ComboBox is visible, but no information is added when I call the Items.Add method. What do I need to implement from the ComboBox class to achieve this? Do I need to do something with the popup? Add a Textblock?

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That doesn't look to me like you're deriving from ComboBox... It looks to me like you're putting a ComboBox inside the ControlTemplate of your custom control.

If you are also deriving your custom control from ComboBox and calling Items.Add on your custom control, then you've basically got two lists of data (one for your custom control and one for the combobox in your controltemplate) and they are not linked in any way.

I'd suggest popping open Expression Blend and taking a look at the control template for a default ComboBox. If you want to derive from ComboBox you can then modify that controltemplate to suit your needs.