CODEWITHSUNDEEP
c#wpfxamldata-bindingattached-properties
Nasai
Nasai

Reputation: 93

Command Binding in ControlTemplate with Attached Property

I'm trying to set up a system that would allow me to attach a string value to a ComboBoxItem and display it next to the ComboBoxItem's content, without having to explicitly nest a StackPanel inside every individual ComboBoxItem or use a custom control.

So what I've done is created a DependencyProperty called "Header" and attach it to the ComboBoxItem, and I've overridden the ComboBoxItem template to contain the stack panel with a TextBlock that binds its Text to the attached Header property of the ComboBoxItem.

The problem I am having is that the only text that ever appears in the TextBlock at runtime is whatever I set the default value of the dependency property to in metadata. Any changes to the attached property on the ComboBoxItems thereafter is not reflected in the TextBlock.

Here is my DependencyProperty definition:

public class AttHeader : DependencyObject
{
    public static readonly DependencyProperty HeaderProperty = DependencyProperty.RegisterAttached("Header", typeof(string), typeof(AttHeader));

    public static void SetHeader(DependencyObject d, string value)
    {
        d.SetValue(HeaderProperty, value);
    }

    public static string GetHeader(DependencyObject d)
    {
        return (string)d.GetValue(HeaderProperty);
    }
}

Here is my style and template:

<Style TargetType="ComboBoxItem">
    <Setter Property="OverridesDefaultStyle" Value="True"/>
    <Setter Property="SnapsToDevicePixels" Value="True"/>
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="ComboBoxItem">
                <StackPanel Orientation="Horizontal">
                    <ContentPresenter />
                    <TextBlock Name="HeaderHost" Text="{Binding Path=(local:AttHeader.Header), RelativeSource={RelativeSource Self}}" />
                </StackPanel>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>

And here is where I create a few ComboBoxItems:

<ComboBox SelectedIndex="0">
    <ComboBoxItem local:AttHeader.Header="Isometric">
        <Image Source="../images/viewTypeIso.png" Stretch="None"/>
    </ComboBoxItem>
    <ComboBoxItem local:AttHeader.Header="Top">
        <Image Source="../images/ViewTypeTop.png" Stretch="None"/>
    </ComboBoxItem>
</ComboBox>

Even setting the value of the attached properties of these ComboBoxItems when they are created has no effect on the TextBlocks within.

I'm assuming the binding is valid, because I can set a default value for the dependency property and each ComboBoxItem will always display that value next to its image.

I've set a breakpoint in SetHeader and it is indeed called when those ComboBoxItems are constructed.

Is there something I am doing wrong or is there some limitation to Binding that I'm unaware of?

Upvotes: 2

Views: 840

Answers (2)

eran otzap
eran otzap

Reputation: 12533

your binding isn't correct , TextBlock is now a child of the ComboBoxItem try binding to :

 <Setter Property="Template">
    <Setter.Value>
        <ControlTemplate TargetType="ComboBoxItem">
            <StackPanel Orientation="Horizontal">
                <ContentPresenter />
                <TextBlock Name="HeaderHost" 
                           Text="{Binding Path=local:AttHeader.Header,
                                  RelativeSource={RelativeSource Mode=FindAncestor
                                  ,AncestorType=ComboBoxItem}}" />
            </StackPanel>
        </ControlTemplate>
    </Setter.Value>
 </Setter>

Upvotes: 2

Nasai
Nasai

Reputation: 93

I still haven't gotten the header binding to work with that implementation, but here's a super easy convenient workaround: Use HeaderedContentControls instead of ComboBoxItems, and instruct your ComboBox to orient the Header Horizontally by implementing the following Style:

<Style TargetType="HeaderedContentControl">
    <Setter Property="OverridesDefaultStyle" Value="True"/>
    <Setter Property="SnapsToDevicePixels" Value="True"/>
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="HeaderedContentControl">
                <StackPanel Orientation="Horizontal">
                    <ContentPresenter />
                    <ContentPresenter ContentSource="Header" />
                </StackPanel>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>

Upvotes: 0

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