WPF TextBlock StringFormat Binding To Parent - wpf

Question

I have been trying to bind the StringFormat of the Text property of a TextBlock to a templated parent.
Here is where I'm trying to set the StringFormat:
<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="clr-namespace:DataFlowControls">
<Style TargetType="{x:Type local:DfcEditTextBox}">
<Setter Property="Margin" Value="-6, 0, -6, 0" />
<Setter Property="FocusVisualStyle" Value="{x:Null}"/>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type local:DfcEditTextBox}">
<TextBlock x:Name="PART_TextBlock"
Padding="2, 0, 0, 0"
Text="{Binding Path=Value, StringFormat=ThisStringFormat, Mode=TwoWay, RelativeSource={RelativeSource TemplatedParent}}">
</TextBlock>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
</ResourceDictionary>
Here is the parent:
<Window x:Class="DataFlowControls.Show.DfcListView"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:dfc="clr-namespace:DataFlowControls;assembly=DataFlowControls"
xmlns:local="clr-namespace:DataFlowControls.Show"
Title="DfcListView" Height="400" Width="500">
<Grid>
<StackPanel>
<dfc:DfcListView Name="lvTradesCollection" ItemsSource="{Binding Path=TradesCollection}" KeyboardNavigation.DirectionalNavigation="Continue" >
<ListView.ItemContainerStyle>
<Style TargetType="ListViewItem">
<Setter Property="HorizontalContentAlignment" Value="Stretch" />
</Style>
</ListView.ItemContainerStyle>
<ListView.Resources>
<DataTemplate x:Key="Date_DataTemplate">
<dfc:DfcEditTextBox Value="{Binding Path=Date, Mode=Twoway, UpdateSourceTrigger=PropertyChanged}" ThisStringFormat='{}{0:dd/MM/yyyy}' HorizontalContentAlignment="Left" IsEditable="true" />
</DataTemplate>
<DataTemplate x:Key="Asset_DataTemplate">
<dfc:DfcEditTextBox Value="{Binding Path=Asset, Mode=Twoway, UpdateSourceTrigger=PropertyChanged}" HorizontalContentAlignment="Left" IsEditable="true" />
</DataTemplate>
<DataTemplate x:Key="Lots_DataTemplate">
<dfc:DfcEditTextBox Value="{Binding Path=Lots, Mode=Twoway, UpdateSourceTrigger=PropertyChanged}" ThisStringFormat='N2' HorizontalContentAlignment="Center" IsEditable="true" />
</DataTemplate>
<DataTemplate x:Key="Price_DataTemplate">
<dfc:DfcEditTextBox Value="{Binding Path=Price, Mode=Twoway, UpdateSourceTrigger=PropertyChanged}" HorizontalContentAlignment="Center" IsEditable="true" />
</DataTemplate>
<DataTemplate x:Key="IsCheap_DataTemplate">
<dfc:DfcEditCheckBox Value="{Binding Path=IsCheap, Mode=Twoway, UpdateSourceTrigger=PropertyChanged}" HorizontalAlignment="Center" IsEditable="true" />
</DataTemplate>
<DataTemplate x:Key="NextTrade_DataTemplate">
<dfc:DfcEditComboBox Value="{Binding Path=NextTrade, Mode=Twoway, UpdateSourceTrigger=PropertyChanged}" ItemsSource="{x:Static local:DfcListView.NextTradeTypes}" IsEditable="true" />
</DataTemplate>
</ListView.Resources>
<ListView.View>
<dfc:DfcGridView>
<dfc:DfcGridViewColumn Header="Date" Width="140" CellTemplate="{StaticResource Date_DataTemplate}" />
<dfc:DfcGridViewColumn Header="Asset" Width="40" CellTemplate="{StaticResource Asset_DataTemplate}" />
<dfc:DfcGridViewColumn Header="Lots" Width="40" CellTemplate="{StaticResource Lots_DataTemplate}" />
<dfc:DfcGridViewColumn Header="Price" Width="50" CellTemplate="{StaticResource Price_DataTemplate}" />
<dfc:DfcGridViewColumn Header="IsCheap" Width="60" CellTemplate="{StaticResource IsCheap_DataTemplate}" />
<dfc:DfcGridViewColumn Header="NextTrade" Width="80" CellTemplate="{StaticResource NextTrade_DataTemplate}" />
</dfc:DfcGridView>
</ListView.View>
</dfc:DfcListView>
<Button Content="Add Row" HorizontalAlignment="Left" Margin="5,5,5,5" Click="AddRow_Click"/>
<Button Content="Update Row" HorizontalAlignment="Left" Margin="5,5,5,5" Click="UpdateRow_Click"/>
</StackPanel>
</Grid>
</Window>
Everything works fine until I include the StringFormat=ThisStringFormat, which mucks it up. But I somehow need to connect the StringFormat to the ThisStringFormat property expressed in the parent. I've experimented with changing StringFormat=ThisStringFormat to try to get to the templated parent, but to no avail.
Any ideas on how to solve this one?

Answer 1

The StringFormat property is just a regular property on BindingBase and regular properties cannot be binding targets only dependency properties can. So the answer is: You cannot not do it that way.
Some possible approaches:
Subclass TextBox and add a string format dependency property to which you can bind providing the required functionality
Augment your view model (if you have one) with a FormattedValue property (probably a bit ugly)
Use a MultiBinding for the Text property. One binding goes to Value and one to the ThisStringFormat of the templated parent. Then write a converter implementing IMultiValueConverter to return the formatted value.