WPF如何通过代码创建一个以画布为内容的数据模板？

Question

I have the data template defined by XAML as below:

<DataTemplate x:Key="PointPushPinItemTemplate">
    <mapControl:MapItem mapControl:MapPanel.Location="{Binding}" >
        <Canvas>
            <Path StrokeThickness="2" Fill="Aqua">
                <Path.Data>
                    <EllipseGeometry RadiusX="10" RadiusY="10"/>
                </Path.Data>
            </Path>
        </Canvas>
    </mapControl:MapItem>
</DataTemplate>

I use below code to create it, but failed:

private DataTemplate PushPinPointDataTemplate()
{
    var pointItemFactory = new FrameworkElementFactory(typeof(MapItem));
    pointItemFactory.SetValue(MapPanel.LocationProperty, new Binding());
    var pointCanvas = new Canvas();
    pointCanvas.Children.Add(new Path
    {
        StrokeThickness = 2.0,
        Fill = new SolidColorBrush(Colors.Yellow),
        Data = new EllipseGeometry {RadiusX = 3, RadiusY = 3}
    });

    //below line always throw exception that FrameworkElementFactory.SetValue can't set a visual value
    pointItemFactory.SetValue(MapItem.ContentProperty, pointCanvas);
    return new DataTemplate
    {
        DataType = typeof(Location),
        VisualTree = pointItemFactory
    };
}

How to achieve this? Previousely, I achieved this if there is no Canvas, but for this case, the Canvas to be the content of a content control. ps: mapControl:MapItem is a UI element which inherited from ListBoxItem mapControl:MapPanel.Location is a attached property

Answer 1

You need to create factories for the Canvas and the Path as well:

private DataTemplate PushPinPointDataTemplate()
{
    var pointItemFactory = new FrameworkElementFactory(typeof(MapItem));
    pointItemFactory.SetValue(MapPanel.LocationProperty, new Binding("."));

    var pathFactory = new FrameworkElementFactory(typeof(Path));
    pathFactory.SetValue(Path.StrokeThicknessProperty, 2.0);
    pathFactory.SetValue(Path.FillProperty, Brushes.Yellow);
    pathFactory.SetValue(Path.DataProperty, new EllipseGeometry { RadiusX = 3, RadiusY = 3 });

    var pointCanvasFactory = new FrameworkElementFactory(typeof(Canvas));
    pointCanvasFactory.AppendChild(pathFactory);

    pointItemFactory.AppendChild(pointCanvasFactory);
    return new DataTemplate
    {
        DataType = typeof(Location),
        VisualTree = pointItemFactory
    };
}

Note that using a FrameworkElementFactory is a deprecated way to programmatically create templates though: https://msdn.microsoft.com/en-us/library/system.windows.frameworkelementfactory(v=vs.110).aspx .

The recommended way to programmatically create a template is to load XAML from a string or a memory stream using the Load method of the XamlReader class.