Concatenate/Format Strings in XAML

Often, you will need to put dynamically concatenated strings on the screen. By this, I mean strings that are built at runtime by concatenating several static and non-static substrings. Something you would do in code as follows:

string formattedString = FirstName + " " + LastName;
// This is better performance-wise since a StringBuilder will be used internally, which means less objects will be created.
string betterFormattedString = string.Format("{0} {1}", FirstName, LastName);

To do this in XAML, you can take the naive approach below.

<StackPanel Orientation="Horizontal"/>
 <TextBlock Text="{Binding Name}"/>
 <TextBlock Text=" "/>
 <TextBlock Text="{Binding LastName}"/>
</StackPanel>

In this example, four UI elements are created: one StackPanel and three TextBlocks. This will have a performance impact since all these elements will need to go through a measurement and layout pass. In case this structure is used once or just a few times, you won’t notice this. However, if it is used in a datatemplate for use inside a list with many elements, you will notice a performance hit.

A better way to concatenate strings in XAML is shown below.

<TextBlock>
  <TextBlock.Text>
    <MultiBinding StringFormat="{}{0} {1}">
      <Binding Path="Name"/>
      <Binding Path="LastName"/>
    </MultiBinding>
  </TextBlock.Text>
</TextBlock>

In this case, we only create one UI element instead of four! Not only is this better performance-wise, it is also much more readable.