Question

我正在尝试制作一个可以进行特殊渲染的WPF UIElement。

问题是我无法使用数据绑定工作PointCollection。在OnRender()的{{1}}内，Points属性为null，这对我没有任何意义。

GraphElement

class GraphElement : UIElement
{
    public static readonly DependencyProperty PointsProperty = DependencyProperty.Register(
        "Points",
        typeof(PointCollection),
        typeof(GraphElement),
        new FrameworkPropertyMetadata(null, FrameworkPropertyMetadataOptions.AffectsRender));            

    public PointCollection Points
    {
        get { return (PointCollection)GetValue(PointsProperty); }
        set { SetValue(PointsProperty, value); }
    }

    protected override void OnRender(DrawingContext drawingContext)
    {
        base.OnRender(drawingContext);

        //Points is null
        Debug.Assert(Points != null);
    }

}

class TestViewModel : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    private PointCollection _viewModelPoints;
    public PointCollection ViewModelPoints
    {
        get { return _viewModelPoints; }
        set
        {
            _viewModelPoints = value;
            if (PropertyChanged != null) PropertyChanged(this, new PropertyChangedEventArgs("ViewModelPoints"));
        }
    }
}

<Window x:Class="TestApp.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="clr-namespace:TestApp"
    Title="MainWindow" Height="350" Width="525">
<Grid>
    <Canvas>
        <local:GraphElement Points="{Binding Path=ViewModelPoints}"/>
    </Canvas>
</Grid>

Answer 1

将GraphElement上的继承从UIElement更改为FrameworkElement（继承UIElement）。这是您拥有DataContext dp等的地方。

class GraphElement : FrameworkElement
{
    //...
}

将您的代码复制到示例项目中（将UIElement更改为FrameworkElement）并且OnRender中的Points不为null。上传了项目here。

WPF：DataBinding自定义UIElement的PointCollection

1 个答案: