TextBox Text Formatting From Style - wpf

Question

I have a MainWindow.XAML
TextBox is added to it
TextBox text binding is done
When I add StringFormat inside binding (in MainWindow.XAML) it works
When I add StringFormat inside Style, it's not working
below is the code from style and MainWindow.xaml
<TextBox Grid.Row="1" Grid.Column="4" Style="{StaticResource TextBoxStyle}" Text="{Binding CustomerAmount,UpdateSourceTrigger=PropertyChanged,Mode=TwoWay}" HorizontalAlignment="Stretch" Margin="10,0,0,0"/>
<Style x:Key="TextBoxStyle" TargetType="{x:Type TextBox}" >
<Setter Property="Text" Value="{Binding Text, RelativeSource={RelativeSource Self},StringFormat='#,###,###,##0.00;(#,###,###,##0.00)'}"></Setter>
</Style>

Answer 1

Well you've basically applied two Text binding's now, one in MainWindow and one in Style.
The Text property set in MainWindow.xaml on the control has precedence over the one you're setting in Style, so the StringFormat you set via Style is actually never applied cos that entire Style.Setter is ignored.
A very rough way to make this work and prove the above statement is try switching your xaml to the following,
<TextBox Grid.Row="1" Grid.Column="4" Style="{StaticResource TextBoxStyle}" Tag="{Binding CustomerAmount,UpdateSourceTrigger=PropertyChanged,Mode=TwoWay}" HorizontalAlignment="Stretch" Margin="10,0,0,0"/>
and Style:
<Style x:Key="TextBoxStyle"
TargetType="{x:Type TextBox}">
<Setter Property="Text"
Value="{Binding Tag,
RelativeSource={RelativeSource Self},
StringFormat='#,###,###,##0.00;(#,###,###,##0.00)',
Mode=TwoWay,
UpdateSourceTrigger=PropertyChanged}" />
</Style>
This will work cos you now have Tag binding in MainWindow and Text in Style. You can switch to a custom Attached property or DP to get the same behavior