CODEWITHSUNDEEP
wpfinheritancedependency-properties
Cool Blue
Cool Blue

Reputation: 6476

The Correct Way to Wrap an Inherited Dependency Property

I have a custom control that derives from ToggleButton and I want to wrap a DP on the base class.
Do I need to do this...

public new bool IsEnabled
{
    get { return (bool)GetValue(IsEnabledProperty); }
    set
    {
        SetValue(IsEnabledProperty, value);
        if (value && IsChecked == null)
            IsChecked = false;
    }
}

or is this ok...

public new bool IsEnabled
{
    get { return base.IsEnabled; }
    set
    {
        base.IsEnabled = value;
        if (value && IsChecked == null)
            IsChecked = false;
    }
}

It seems to work the same both ways but I don't know if there are any hidden problems.

Upvotes: 0

Views: 252

Answers (1)

Clemens
Clemens

Reputation: 128146

You must not call anything else than GetValue and SetValue in the CLR wrapper of a dependency property. The reason is explained in the XAML Loading and Dependency Properties article on MSDN.

Instead of adding a new CLR wrapper, you could call AddOwner on the base class dependency property field to register another PropertyChangedCallback:

public class MyToggleButton : ToggleButton
{
    static MyToggleButton()
    {
        IsEnabledProperty.AddOwner(typeof(MyToggleButton),
            new FrameworkPropertyMetadata(IsEnabledPropertyChanged));
    }

    private static void IsEnabledPropertyChanged(
        DependencyObject o, DependencyPropertyChangedEventArgs e)
    {
        var myToggleButton = (MyToggleButton)o;

        if ((bool)e.NewValue && !myToggleButton.IsChecked.HasValue)
        {
            myToggleButton.IsChecked = false;
        }
    }
}

Upvotes: 1

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