绑定属性不是依赖项属性

Question

我想将媒体元素的位置绑定到它的模型视图。 我知道该属性不是依赖项属性。 所以这样尝试，我在网上找到了一个代码

<MediaElement Source="{Binding CurrentClip.Path, Converter={StaticResource converter}, UpdateSourceTrigger=PropertyChanged}" Stretch="Uniform" local:MediaElementHelper.Postion="{Binding CurrentClip.Postion}"

MediaElementHelper

class MediaElementHelper
{
    public static readonly DependencyProperty PostionProperty =
        DependencyProperty.RegisterAttached("Position",
        typeof(bool), typeof(MediaElement),
        new FrameworkPropertyMetadata(false, PostionPropertyChanged));

    private static void PostionPropertyChanged(DependencyObject obj, DependencyPropertyChangedEventArgs e)
    {
        var richEditControl = obj as MediaElement;

        if (richEditControl != null)
        {
            richEditControl.Position = (TimeSpan)e.NewValue;
        }
    }
    public static void SetPostion(UIElement element, TimeSpan value)
    {
        element.SetValue(PostionProperty, value);
    }
    public static TimeSpan GetPostion(UIElement element)
    {
        return (TimeSpan)element.GetValue(PostionProperty);
    }
}

[错误]无法在'MediaElement'类型的'SetPostion'属性上设置'Binding'。 只能在DependencyObject的DependencyProperty上设置“绑定”。

我究竟做错了什么？

Answer 1

您面临的问题是由于您的AttachedProperty访问器名称错误。

代替GetPostion和SetPostion它们应该分别是GetPosition和SetPosition并且在使用AttachedProperty时，它们应该是GetPosition local:MediaElementHelper.Position （不是Postion）。

另外，您还需要根据其他答案的建议更新“ Type和default value 。 但是不需要从DependancyObject派生您的类，而是可以使您的类static 。

Answer 2

我唯一看到的错误是您的附加财产未注册为正确的类型。

public static readonly DependencyProperty PostionProperty =
    DependencyProperty.RegisterAttached("Position",
    typeof(TimeSpan), typeof(MediaElement),
    new FrameworkPropertyMetadata(TimeSpan.FromSecond(0), ChangeHandler));

想通了我应该为附加属性建立一个模板。

public class AttachedPropertyClass 
{
    private static readonly {PropertyType} DefaultValue = ...;

    public static readonly DependencyProperty {PropertyName}Property
       = DependencyProperty.RegisterAttached("{PropertyName}",
    typeof({PropertyType}), typeof({AttachedType}),
    new FrameworkPropertyMetadata(DefaultValue, PostionPropertyChanged));;

    public static void Set{PropertyName}(DependencyObject d, {PropertyType} value)
    {
        d.SetValue({PropertyName}, value);
    }

    public static {PropertyType} Get{PropertyName}(DependencyObject DepObject)
    {
        return ({PropertyType})DepObject.GetValue({PropertyName});
    }

    private static void ChangeHandler(DependencyObject obj, DependencyPropertyChangedEventArgs e);
}

Answer 3

<MediaElement Source="{Binding CurrentClip.Path, Converter={StaticResource converter}, UpdateSourceTrigger=PropertyChanged}" Stretch="Uniform" local:MediaElementHelper.Position ="{Binding CurrentClip.Postion}">

所做的更改

public static class MediaElementHelper 
{
    private static readonly TimeSpan DefaultValue = new TimeSpan(0);

    public static readonly DependencyProperty PositionProperty =
        DependencyProperty.RegisterAttached("Position",
        typeof(TimeSpan), typeof(MediaElementHelper),
        new FrameworkPropertyMetadata(DefaultValue, PositionPropertyChanged));

    private static void PositionPropertyChanged(DependencyObject obj, DependencyPropertyChangedEventArgs e)
    {
        var richEditControl = obj as MediaElement;

        if (richEditControl != null)
        {
            richEditControl.Position = (TimeSpan)e.NewValue;
        }
    }
    public static void SetPosition(UIElement element, TimeSpan value)
    {
        element.SetValue(PositionProperty, value);
    }

    public static TimeSpan GetPosition(UIElement element)
    {
        return (TimeSpan)element.GetValue(PositionProperty);
    }
}