What is the WPF XAML Data Binding equivalent of String.Format?

Question

Or, to be more clear, how can I format a block of text (in my case, to be included within a tooltip) such that some portions of the text come from bound values.

In plain C# I would use:

_toolTip.Text = string.Format("{1:#0}% up, {2:#0}% down",
    Environment.NewLine, percentageOne, percentage2);

However the WPF XAML markup for a Text property seems able to contain only a single binding. The curly braces gave me high hopes, but this isn't possible:

<Element>
  <Element.Tooltip>
    <!-- This won't compile -->
    <TextBlock Text="{Binding Path=PercentageOne}% up, {Binding Path=PercentageTwo}% down"/>
  </Element.Tooltip>
</Element>

I read that the Run.Text property is not a dependency property and can therefore not be bound.

Is there a way I can perform this formatting in XAML?

Answer 1

You can use MultiBinding + StringFormat (requires WPF 3.5 SP1):

<TextBox.Text>
    <MultiBinding StringFormat="{}{1:#0}% up, {2:#0}% down">
      <Binding Path="PercentageOne" />
      <Binding Path="PercentageTwo"/>
    </MultiBinding>
</TextBox.Text>

Regarding Run.Text - you can't bind to it but there are some workarounds:

• http://fortes.com/2007/03/20/bindablerun/
• http://paulstovell.net/blog/index.php/attached-bindablerun/

Answer 2

I would split into multiple textblocks, binding each one with the StringFormat={0:P} in the binding as such:

<TextBox Text="{Binding Something, StringFormat=\{0:P\}}" />

See this post for examples:Lester's WPF Blog on StringFormat

Checkout VS2010 - The binding from properties includes formatting in the options.

Answer 3

If you're using 3.5 SP1, Aku's answer is the way to go. If you're not, you can use the FormatConverter from my WPF Converters library.

Answer 4

The way I've solved this in the past is actually to break the TextBlock you have in your listing up into several TextBlocks. Try something like this:

<Element>
  <Element.Tooltip>
    <StackPanel Orientation="Horizontal">
      <TextBlock Text="{Binding Path=PercentageOne}"/>
      <TextBlock Text="% up, "/>
      <TextBlock Text="{Binding Path=PercentageTwo}"/>
      <TextBlock Text="% down"/>
    </StackPanel>
  </Element.Tooltip>
</Element>

Alternately you can create something like a StringFormatConverter, which could take the format string as a parameter, and use a MultiBinding to pass it the parameters. See this link for MultiBindings:

MultiBinding Info

And this one for info on converters:

Converters Info

You can pretty easily imagine a converter that takes "object[] values" instead of "object value" as it's first parameter, and passes those on to the Format function.

Answer 5

As far as I know, WPF doesn't do what you want. You do have a much more powerful (albeit more involved) solution.

Take a look at the IValueConverter interface.

MSDN HowTo link here

EDIT

Based on aku's answer, and your assertion that you can't use 3.5 SP1, here's an alternative.

Take a look at Phil Haack's recent series of posts on string formatting:

• Fun With Named Formats, String Parsing, and Edge Cases
• Named Formats Redux

Create a ValueConverter as that takes the format as a property. You should then be able to bind your data object and have it format based on your defined format (using property name instead of position).