CODEWITHSUNDEEP
c#wpfcallbackviewmodeldependency-properties
Ludovic Wagner
Ludovic Wagner

Reputation: 117

How to add a UserControl specific ViewModel but still reach the Dependency Property changed callback in WPF

I would like to create a WPF class library based on a TreeView to visualize JSON strings.

I define a JsonProperty DependencyProperty which I wan't to use to pass the JSON string. I'm able to get the string in the JsonChangedCallback without DataContext. When I add a DataContext to the ViewModel, the JsonChangedCallback is not longer reached. I'm not so sure how I will achieve it yet, but I believe that a specific ViewModel will be required to handle the TreeView node expansions.

For the time being, I don't want to load the JSON string from a file, but directly provide it from the consumer app. I'll probably change it later on if performances matter.

I believe that if I don't specified a ViewModel in the View of the class library it takes the one from the consumer app. I don't get any binding error though.

How can I specified a specific ViewModel, but still reach the JsonChangedCallback ?

<UserControl xmlns:visualizer="clr-namespace:Visualizer;assembly=Visualizer.Desktop">

    <visualizer:JsonVisualizer Json="{Binding Json, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" />

</UserControl>

<TreeView x:Class="Visualizer.JsonVisualizer">

    <TreeView.Resources>

        <!--  Not sure if something like that can help..  -->
        <Style TargetType="{x:Type local:JsonVisualizer}">

            <Setter Property="Json" Value="{Binding JsonProperty, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged, RelativeSource={RelativeSource Self}}" />

        </Style>

    </TreeView.Resources>

</TreeView>

public partial class JsonVisualizer : TreeView
{
    #region Public Static Readonly Members

    public static readonly DependencyProperty JsonProperty =
        DependencyProperty.Register(
            nameof(Json),
            typeof(string),
            typeof(JsonVisualizer),
            new PropertyMetadata(null, JsonChangedCallback));

    public string Json
    {
        get => (string)GetValue(JsonProperty);
        set => SetValue(JsonProperty, value);
    }

    public JsonVisualizer()
    {
        InitializeComponent();

        //DataContext = new JsonVisualizerViewModel();
    }

    private static void JsonChangedCallback(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        var json = e.NewValue;
        
        // Code reached if no DataContext specified in the constructor.
    }
}

Upvotes: 0

Views: 89

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