XAML and TargetNullValue

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.

`TargetNullValue`

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}">
    <ListView.ItemTemplate>
        <DataTemplate>
            <Label>
                <Label.Resources>
                    <ResourceDictionary>
                        <Syncfusion:SfBusyIndicator x:Key="Busy" x:Shared="False" IsBusy="True" AnimationType="Message" /> (1)
                    </ResourceDictionary>
                </Label.Resources>
                <Label.Content>
                    <Binding Path="Value" TargetNullValue="{StaticResource Busy}" /> (2)
                </Label.Content>
            </Label>
        </DataTemplate>
    </ListView.ItemTemplate>
</ListView>

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.

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.