Question

I am new to xaml, i have following code below, my question is how can i call InvalidForeground from c# code to change the color of checkbox text?

<ControlTemplate x:Key="ItemTemplate"
                                 TargetType="ListViewItem">
                    <StackPanel Orientation="Horizontal">                    
                        <CheckBox x:Name="CkBoxVisual">
                            <CheckBox.IsChecked>
                                <Binding Path="IsSelected"
                                         Mode="TwoWay">
                                    <Binding.RelativeSource>
                                        <RelativeSource Mode="TemplatedParent" />
                                    </Binding.RelativeSource>
                                </Binding>                                
                            </CheckBox.IsChecked>
                            <DataTrigger Binding="{Binding InvalidForeground, RelativeSource={RelativeSource Mode=FindAncestor, AncestorType={x:Type Window}}}" Value="true">
                                <Setter TargetName="CkBoxVisual" Property="Foreground" Value="Red"/>
                            </DataTrigger>                       
                        </CheckBox>                    
                        <ContentPresenter />                    
                    </StackPanel>
                </ControlTemplate>

Answer 1

In your code, you are not calling anything. In it, you’re hoping a change of dependency property..

But a control of type Window does not have a dependency property with the name: “InvalidForeground”.
This trigger will never be triggered.
What is your goal, change a property or be notified of a change (trigger)?

---

Edit: There are a number of rules you must follow:

1) The control referenced in Binding property from DataTrigger (RelativeSource):

Binding="{Binding Path=InvalidForeground, RelativeSource={RelativeSource Mode=FindAncestor, AncestorType={x:Type Window}}}"

Must have a dependency property called “InvalidForeground”, which works correctly, based on this, will not work:

{x:Type Window}

its type must be declared, will work, for example:

{x:Type my:ControlName}

2) A property changed by a Trigger or DataTrigger can never be explicitly stated, for example. Will not work:

<TextBlock Text="{Binding Any}" Foreground="#FFCCCCCC">
    <TextBlock.Style>
        <Style TargetType="TextBlock">
            <Style.Triggers>
                <DataTrigger Binding="{Binding RelativeSource={RelativeSource AncestorType=TabItem, Mode=FindAncestor}, Path=IsSelected}" Value="True">
                    <Setter Property="Foreground" Value="Black"/>
                </DataTrigger>
            </Style.Triggers>
        </Style>
    </TextBlock.Style>
</TextBlock>

Will work:

<TextBlock Text="{Binding Any}">
    <TextBlock.Style>
        <Style TargetType="TextBlock">
            <Setter Property="Foreground" Value="#FFCCCCCC"/>
            <Style.Triggers>
                <DataTrigger Binding="{Binding RelativeSource={RelativeSource AncestorType=TabItem, Mode=FindAncestor}, Path=IsSelected}" Value="True">
                    <Setter Property="Foreground" Value="Black"/>
                </DataTrigger>
            </Style.Triggers>
        </Style>
    </TextBlock.Style>
</TextBlock>

3) Check the operation of Bindings using RelativeSource they have some peculiarities (you should know a little about the visual tree of WPF).

http://msdn.microsoft.com/en-us/library/ms743599.aspx

4) You should check that the binding is working properly and can follow these steps:
http://www.codeproject.com/Articles/244107/Debugging-WPF-data-bindings