XAML and TargetNullValue

Briefly about setting a specific control when the value is null.

XAML has tremendous capabilities and I guess most of them are still unknown to me, and the few that I do learn often fly out of my mind due to unit usage. In this note, I would like to keep my knowledge of {Binding TargetNullValue="…​"} for longer because I find it useful and definitely speed up application development.


By default, in most examples I have seen TargetNullValue being used like this:

Example of using TargetNullValue.
<Label Content="{Binding MyText TargetNullValue=You did not specify a value}" />

Nowhere so far have I encountered the use of another control in place of TargetNullValue, but it is possible! There are a few pitfalls when doing this, but everything is explained in the example below:

Example of using TargetNullValue, where the value is another XAML control
<ListView ItemsSource="{Binding Properties}">
                        <Syncfusion:SfBusyIndicator x:Key="Busy" x:Shared="False" IsBusy="True" AnimationType="Message" /> (1)
                    <Binding Path="Value" TargetNullValue="{StaticResource Busy}" /> (2)
1 The element we want to display when our value is null. Note that it is inside the ResourceDictionary dictionary, and most importantly it is marked x:Shared="False" - this is essential. Without this, using a given element repeatedly will result in errors such as, that our SfBusyIndicator will only display in one place.
2 Proper binding definition - note that the value is set by standard, and TargetNullValue refers directly to our dictionary using the StaticResource construct.

With this solution, we get an independent loading indicator anywhere the value is null! Note also that using this technique, I was forced to make a custom column template for GridView - in the course of my efforts, I was unable to get this working in a simpler way.

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Ilustracja 1. An example of how the code works, where the control is the value for TargetNullValue. This is a gif, so it should move.
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