Binding StringFormat

Since BindingBase.StringFormat is not a dependency property, I do not think that you can bind it. If the formatting string varies, I'm afraid you will have to resort to something like this

<TextBlock Text="{Binding MyFormattedProperty}" />

and do the formatting in your view model. Alternatively, you could use a MultiBinding and a converter (example code untested):

<TextBlock>    <TextBlock.Text>        <MultiBinding Converter="{StaticResource myStringFormatter}">            <Binding Path="MyProperty" />            <Binding Path="MyFormatString" />        </MultiBinding>    </TextBlock.Text></TextBlock>public class StringFormatter : IMultiValueConverter{    public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)    {        return string.Format((string)values[1], values[0]);    }    ...}

<TextBlock>    <TextBlock.Text>        <MultiBinding StringFormat="{}{0},{1}">            <Binding Path="MyProperty" />            <Binding Path="MyFormatString" />        </MultiBinding>    </TextBlock.Text></TextBlock>

The String Formatting is a display setting and therefore should live close to the UI layer, you can either declare it in the Xaml or have formatted string properties on a ViewModel and perform the formatting in the Get of those properties and bind the TextBlock to it the ViewModel properties. It would source its data from the original datasource.