WPF StringFormat on Label Content

Question

I want to format my string binding as Amount is X where X is a property bound to a label.

I've seen many examples but the following doesn't work:

<Label Content="{Binding Path=MaxLevelofInvestment,     StringFormat='Amount is {0}'}" /> 

I've also tried these combinations:

StringFormat=Amount is {0} StringFormat='Amount is {}{0}' StringFormat='Amount is \{0\}' 

I even tried changing the binding property's datatype to int, stringand double. Nothing seems to work. This is a very common use case but doesn't seem to be supported.

Answer 1

The reason this doesn't work is that the Label.Content property is of type Object, and Binding.StringFormat is only used when binding to a property of type String.

What is happening is:

1. The Binding is boxing your MaxLevelOfInvestment value and storing it the Label.Content property as a boxed decimal value.
2. The Label control has a template that includes a ContentPresenter.
3. Since ContentTemplate is not set, ContentPresenter looks for a DataTemplate defined for the Decimal type. When it finds none, it uses a default template.
4. The default template used by the ContentPresenter presents strings by using the label's ContentStringFormat property.

Two solutions are possible:

• Use Label.ContentStringFormat instead of Binding.StringFormat, or
• Use a String property such as TextBlock.Text instead of Label.Content

Here is how to use Label.ContentStringFormat:

<Label Content="{Binding Path=MaxLevelofInvestment}" ContentStringFormat="Amount is {0}" /> 

Here is how to use a TextBlock:

<TextBlock Text="{Binding Path=MaxLevelofInvestment, StringFormat='Amount is {0}'}" /> 

Note: For simplicity I omitted one detail in the above explanation: The ContentPresenter actually uses its own Template and StringFormat properties, but during loading these are automatically template-bound to the ContentTemplate and ContentStringFormat properties of the Label, so it seems as if the ContentPresenter is actually using the Label's properties.

Answer 2

Make a universal StringFormatConverter : IValueConverter. Pass your format string as ConverterParameter.

Label Content="{Binding Amount, Converter={...myConverter}, ConverterParameter='Amount is {0}'" 

Also, make StringFormatMultiConverter : IMultiValueConverter when you need more than one object in format string, for instance, Completed {0} tasks out of {1}.