DataTrigger for Textblock

Question

I have a Textblock that I'm trying to change the value of the Text property if a property is True or False. The issue I'm having is that the flag could be changed on different events on the screen (onchange events from other combo boxes).

I'm not sure how to get this datatrigger to work as I don't think it know when the value has been changed.

<TextBlock Grid.Row="9" HorizontalAlignment="Right" Text="Some Old Value:" VerticalAlignment="Center">
    <TextBlock.Style>
        <Style TargetType="{x:Type TextBlock}">
             <Style.Triggers>
                 <DataTrigger Binding="{Binding IsChecked}" Value="False" >
                     <Setter Property="Text" Value="Different Text:"/>
                 </DataTrigger>
             </Style.Triggers>
         </Style>
     </TextBlock.Style>                                
</TextBlock>

I see in some comboboxes there is the UpdateSourceTrigger=PropertyChanged, but I don't see a way to implement that in the TextBlock.

Answer 1

First of all set default Text in style setter, otherwise no matter whether your triggers fires successfully or not, Text won't take value from Style setter because of Dependency property value precedence order. Local value has higher precedence than style setter values.

<TextBlock Grid.Row="9" HorizontalAlignment="Right" VerticalAlignment="Center">
    <TextBlock.Style>
        <Style TargetType="{x:Type TextBlock}">
             <Setter Property="Text" Value="Some Old Value:"/>
             <Style.Triggers>
                 <DataTrigger Binding="{Binding IsChecked}" Value="False" >
                     <Setter Property="Text" Value="Different Text:"/>
                 </DataTrigger>
             </Style.Triggers>
         </Style>
     </TextBlock.Style>                                
</TextBlock>

Second, if IsChecked property resides in your ViewModel (implementing INotifyPropertyChanged) and TextBlock DataContext is rightly pointing to ViewModel instance, you don't have to worry about it.

Just make sure whenever property IsChecked changes in ViewModel a PropertyChanged event gets raised so that UI can listen to that and updates itself.