How to Bind an another Control on the Setter Value Property by using a Trigger?

Question

i've a little Problem with the Databinding in WPF an hope you can help me.

I want to bind the SelectedDate Parameter of a DatePicker on a TextBlock, but only when a CheckBox is checked. The CheckBox and the TextBlock are in a DataView, the DatePicker is outside.

In the Moment i try to use it with a Trigger an set the Binding in the Value-Property in the Setter Part.

<TextBlock Text="">
    <TextBlock.Style>
        <Style TargetType="TextBlock">
            <Style.Triggers>
                <DataTrigger Binding="{Binding Path=IsChecked}" Value="True">
                    <Setter Property="Text" Value="{Binding ElementName=StandartPitBis, Path=SelectedDate, StringFormat='dd.MM.yyyy'}" />
                </DataTrigger>
            </Style.Triggers>
        </Style>
    </TextBlock.Style>
</TextBlock>

But this will not works. Has anywone a Tipp what i can do?

Here is the Code-Parts there i'm using:

Inside the GridView

The CheckBox

<GridViewColumn>
    <GridViewColumn.CellTemplate>
        <DataTemplate>
            <CheckBox Content="" x:Name="check_Anlage" IsChecked="{Binding Path=IsChecked}" />
        </DataTemplate>
    </GridViewColumn.CellTemplate>
</GridViewColumn>

The TextBlock

<TextBlock Text="">
    <TextBlock.Style>
        <Style TargetType="TextBlock">
            <Style.Triggers>
                <DataTrigger Binding="{Binding Path=IsChecked}" Value="True">
                    <Setter Property="Text" Value="{Binding ElementName=StandartPitBis, Path=SelectedDate, StringFormat='dd.MM.yyyy'}" />
                </DataTrigger>
            </Style.Triggers>
        </Style>
    </TextBlock.Style>
</TextBlock>

Outside the GridView

The DatePicker

<DatePicker Grid.Column="1" Margin="0,5,0,5" SelectedDate="{x:Static sys:DateTime.Now}" x:Name="StandartPitVon" />

What i want to make is, that the SelectedDate from the DatePicker is shown in the TextBlock, but only when the CheckBox is Checked.

Thanks a lot

Answer 1

So. I've found the Problem. The Problem is, when a Property is set in the Object self, then it can't be overridet. When you need a Default-Value and a Trigger, then you must define the Default-Value in the Style too.

Example:

<TextBlock>
    <TextBlock.Style>
        <Style TargetType="TextBlock">
            <Setter Property="Text" Value="{x:Null}" />
            <Style.Triggers>
                <DataTrigger Binding="{Binding Path=IsChecked}" Value="True">
                    <Setter Property="Text" Value="{Binding ElementName=StandartPitVon, Path=SelectedDate, StringFormat='dd.MM.yyyy'}" />
                </DataTrigger>
            </Style.Triggers>
        </Style>
    </TextBlock.Style>
</TextBlock>