自定义属性上的WPF动态值

Question

I Have a User Control which contains Expander and few other controls.

User control have a custom "XBackground" property which actually sets the background only for the Expander.

    public Brush XBackground
    {
        get
        {
            return expander.Background;
        }
        set
        {
            expander.Background = value;
        }
    }

When I use my user control, background can only be set statically, not dynamically. Debugger says that only DependencyProperty can be set via dynamic resource. And here I'm stuck. I tried to register dependency property on my XBackground property but I'm receiving an error saying "A 'DynamicResourceExtension' can only be set on a DependencyProperty of a DependencyObject."

Here is my try of registering dependency property:

public static readonly DependencyProperty BcgProperty = DependencyProperty.Register("XBackground", typeof(Brush), typeof(Expander));

Answer 1

Minor mistake:

public static readonly DependencyProperty BcgProperty = DependencyProperty.Register("XBackground", typeof(Brush), typeof( YourCustomUserControl ));

Full version:

public static readonly DependencyProperty XBackgroundProperty 
            = DependencyProperty.Register("XBackground", typeof(Brush), typeof(YourCustomUserControl));
public Brush XBackground
{
    get { return (Brush) GetValue( XBackgroundProperty ); }
    set { SetValue( XBackgroundProperty, value ); }
}

Answer 2

Owner class in Register is not an Expander, but the name of the class in which your DependencyProperty is registered. Try this:

    public Brush XBackground
    {
        get { return (Brush)GetValue(XBackgroundProperty); }
        set { SetValue(XBackgroundProperty, value); }
    }

    // Using a DependencyProperty as the backing store for XBackground.  This enables animation, styling, binding, etc...
    public static readonly DependencyProperty XBackgroundProperty =
        DependencyProperty.Register("XBackground", typeof(Brush), typeof(/typeof your UserControl goes here/), new PropertyMetadata(null));

Answer 3

You must not use typeof(Expander) , but instead the type of your UserControl as the ownerType argument of the Register method. In addition you'll also have to call GetValue and SetValue in the property wrapper.

Besides that, you would also have to a register a PropertyChangedCallback with the property metadata, to get notified about property value changes:

public partial class YourUserControl : UserControl
{
    ...

    public Brush XBackground
    {
        get { return (Brush)GetValue(XBackgroundProperty); }
        set { SetValue(XBackgroundProperty, value); }
    }

    public static readonly DependencyProperty XBackgroundProperty =
        DependencyProperty.Register(
            "XBackground",
            typeof(Brush),
            typeof(YourUserControl),
            new PropertyMetadata(null, XBackgroundPropertyChanged));

    private static void XBackgroundPropertyChanged(
        DependencyObject obj, DependencyPropertyChangedEventArgs e)
    {
        var userControl = (YourUserControl)obj;
        userControl.expander.Background = (Brush)e.NewValue;
    }
}

---

An alternative to the PropertyChangedCallback would be to bind the Expander's Background property to the UserControl's XBackground property in XAML:

<UserControl ...>
    ...
    <Expander Background="{Binding XBackground,
        RelativeSource={RelativeSource Mode=FindAncestor, AncestorType=UserControl}}"/>
    ...
</UserControl>