WPF: Bind to custom dependency property in a style

Question

I have a custom dependency property that I would like to bind to and pass into a value converter within a style. Here is the code:

   <Window.Resources>
      <local:Conv x:Key="MyConv" />

      <Style x:Key="TextBoxField" TargetType="{x:Type TextBox}">
         <Setter Property="DataContext">
            <Setter.Value>
               <MultiBinding Converter="{StaticResource MyConv}">
                  <Binding RelativeSource="{RelativeSource AncestorType={x:Type Window}}" />
                  <Binding Path="local:FieldName.FieldId" RelativeSource="{RelativeSource AncestorType={x:Type TextBox}}" />
               </MultiBinding>
            </Setter.Value>
         </Setter>
      </Style>
   </Window.Resources>
   <Grid>
      <TextBox local:FieldName.FieldId="FirstName" Style="{StaticResource TextBoxField}"/>
   </Grid>

I have set my custom dependency property FieldId on the TextBox. In the style, I am trying to reference it to pass into my converter. The Window passes in correctly, but FieldId comes in as an Unset value.

I have tried various RelativeSource's, referencing "local" or not "local" while referencing the custom property, etc.

FieldName.FieldId appears to be an attached property, which must be put in parentheses in a Binding Path, i.e. Path="(local:FieldName.FieldId)". See PropertyPath for Objects in Data Binding. — Clemens
– Clemens, Commented Jan 26 at 22:48
Yes, FieldName.FieldId is an attached property. I changed the code, wrapping it in parentheses as you have done, but the result didn't change. I'm still not getting FieldId passed into the converter function. I also tried removing the RelativeSource reference and that didn't make a difference either. — Seated
– Seated, Commented Jan 27 at 4:23

Seated · Accepted Answer · 2025-01-27 04:42:33Z

0

Okay, I stumbled (emphasis on "stumbled") on the answer.

I named the TextBox control "Test" and added "ElementName="Test"" to the FieldId line in the style and it worked. So I knew there was some way to accomplish this.

I removed "Test", putting the Style back the way it was. Then I changed the line to the following:

<Binding Path="(local:FieldName.FieldId)" RelativeSource="{RelativeSource Self}" />

The control's attached prophet FieldId is now correctly passed into the converter.

answered Jan 27 at 4:42

Seated

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