How to get bound data from Dependency property that created in sub class-CodePudding

In background property for instance we can do like this

<cs:CustomControl.Background>
    <SolidColorBrush Color="{Binding BackGround}"/>
</cs:CustomControl.Background>

SolidColorBrush is a separate class and contains separate dependency properties, and it working fine and the background property is updating as expected.

I'm trying to do the same concept on my CustomControl.

I have create a subclass with dependency property like this

public class SubClass : DependencyObject
{
    public double SubProperty1
    {
        get { return (double)GetValue(SubProperty1Property); }
        set { SetValue(SubProperty1Property, value); }
    }

    // Using a DependencyProperty as the backing store for SubProperty1.  This enables animation, styling, binding, etc...
    public static readonly DependencyProperty SubProperty1Property =
        DependencyProperty.Register("SubProperty1", typeof(double), typeof(SubClass), new PropertyMetadata(10.0d, OnSubProperty1Changed));

    private static void OnSubProperty1Changed(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        //never called;
    }

    public string SubProperty2
    {
        get { return (string)GetValue(SubProperty2Property); }
        set { SetValue(SubProperty2Property, value); }
    }

    // Using a DependencyProperty as the backing store for SubProperty1.  This enables animation, styling, binding, etc...
    public static readonly DependencyProperty SubProperty2Property =
        DependencyProperty.Register("SubProperty2", typeof(string), typeof(SubClass), new PropertyMetadata("test", OnSubProperty2Changed));

    private static void OnSubProperty2Changed(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        //never called;
    }
}

And in my main class for my custom tool, I created dependency property as follows:

public SubClass MainProperty
{
    get { return (SubClass)GetValue(MainPropertyProperty); }
    set { SetValue(MainPropertyProperty, value); }
}

// Using a DependencyProperty as the backing store for MainProperty.  This enables animation, styling, binding, etc...
public static readonly DependencyProperty MainPropertyProperty =
        DependencyProperty.Register("MainProperty", typeof(SubClass), typeof(CustomControl), new PropertyMetadata((SubClass)null, OnMainPropertyChanged));

private static void OnMainPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
    // called when object created only and not called again when the property changed on the UI
}

Then in my WPF window I did as following

<cs:CustomControl.MainProperty>
    <cs:SubClass SubProperty1="{Binding Length}" SubProperty2="{Binding Title}"/>
</cs:CustomControl.MainProperty>

my code compiles but dependecy properties not updating and callback function not called when the viewmodel update

how can I make this work? and what do I miss I hope there is any idea with detailed code thanks in advance

CodePudding user response：

In the Output Window in Visual Studio you should have seen something like

System.Windows.Data Error: 2 : Cannot find governing FrameworkElement or FrameworkContentElement for target element. ...

when you debug your application. This is because your control and its DependencyObject property do not form a logical tree.

In order to build a logical tree, SubClass must derive from Freezable

public class SubClass : Freezable
{
   ...

    protected override Freezable CreateInstanceCore()
    {
        return new SubClass();
    }
}

and CustomControl must add SubClass instances to its logical children collection:

private static void OnMainPropertyChanged(
    DependencyObject o, DependencyPropertyChangedEventArgs e)
{
    if (e.OldValue != null)
    {
        ((CustomControl)o).RemoveLogicalChild(e.OldValue);
    }
    if (e.NewValue != null)
    {
        ((CustomControl)o).AddLogicalChild(e.NewValue);
    }
}