如何在 MouseHit 上更改 DrawingVisual 的颜色

Question

以下代码改编自 Adam Nathan 发布的 WPF 4.5 第 502 页的代码示例。

按照那里的建议，我创建了一个 class VisualHostClass 来“托管”DrawingVisual 列表，从而使它们可以显示。这到目前为止有效。

现在我想通过更改显示视觉对象的颜色来响应鼠标左键单击。代码在方法 HitTestCallback.

中

通过包含的 Trace.WriteLine 语句，我可以看到相关行

drw.Brush = Brushes.Red;

达到

之后属性 Brush 有了新的值。但是：显示没有变化，点击后的DrawingVisual还是黄色（创建时使用的画笔颜色）

can/should 我在这里做什么？（我绝对是 WPF 的初学者）。

提前感谢所有的回答！

    public partial class VisualHostClass : FrameworkElement
    {
        public VisualHostClass()
        {
 
        }

        public List<DrawingVisual> myVisuals = new List<DrawingVisual>();

        public void AddVisual(DrawingVisual dvs)
        {
            myVisuals.Add(dvs);
            AddVisualChild(dvs);
            AddLogicalChild(dvs);

        }

        protected override int VisualChildrenCount
        {
            get { return myVisuals.Count; }
        }

        protected override Visual GetVisualChild(int index)
        {
            if (index < 0 || index >= myVisuals.Count)
            {
                throw new ArgumentOutOfRangeException("index");
            }

            return myVisuals[index];
        }

        public void removeAllChilds()
        {
            foreach (DrawingVisual dvs in myVisuals)
            {
                RemoveVisualChild(dvs);
                RemoveLogicalChild(dvs);
            }
            myVisuals.Clear();
        }

        protected override void OnMouseLeftButtonDown(MouseButtonEventArgs e)
        {
            base.OnMouseLeftButtonDown(e);

            Point location = e.GetPosition(this);

            VisualTreeHelper.HitTest(this, null,
                new HitTestResultCallback(HitTestCallback),
                new PointHitTestParameters(location));

        }

        public HitTestResultBehavior HitTestCallback(HitTestResult result)
        {
            if (result.VisualHit.GetType() == typeof(DrawingVisual))
            {
                DrawingVisual dv = result.VisualHit as DrawingVisual;

                Trace.WriteLine("HitTestCallback: dv = " + dv.ToString());

                foreach(GeometryDrawing drw in dv.Drawing.Children)
                {
                    Trace.WriteLine("HitTestCallback: drw = " + drw.ToString());
                    
                    Trace.WriteLine("HitTestCallback: drw.Geometry = " + drw.Geometry.ToString());

                    Trace.WriteLine("HitTestCallback: drw.Brush = " + drw.Brush.ToString());

                    drw.Brush = Brushes.Red;

                    Trace.WriteLine("HitTestCallback: drw.Brush = " + drw.Brush.ToString());

                    Trace.WriteLine("HitTestCallback: drw.IsFrozen = " + drw.IsFrozen.ToString());

                }
 
            }

            return HitTestResultBehavior.Continue;
        }
    }
}

编辑：经过一些实验后，下面的工作（但它对我来说并不令人满意，因为我只能更改 SolidColorBrush 的 Color，但不能更改 Brush 本身):

   public void ChangeBrush(DrawingVisual dv)
    {
        Trace.WriteLine("HitTestCallback: dv = " + dv.ToString());

        foreach (Drawing drw1 in dv.Drawing.Children)
        {
            if (drw1 is GeometryDrawing)
            {
                GeometryDrawing drw = drw1 as GeometryDrawing;

                Trace.WriteLine("HitTestCallback: drw = " + drw.ToString());

                Trace.WriteLine("HitTestCallback: drw.Geometry = " + drw.Geometry.ToString());

                Trace.WriteLine("HitTestCallback: drw.Brush = " + drw.Brush.ToString());

                Trace.WriteLine("HitTestCallback: drw.IsFrozen = " + drw.IsFrozen.ToString());
                Trace.WriteLine("HitTestCallback: drw.Brush.IsFrozen = " + drw.Brush.IsFrozen.ToString());

                // does not work
                //SolidColorBrush newBrush = new SolidColorBrush(Colors.Red);

                //newBrush.Freeze();

                //drw.Brush = newBrush;

                // works with drw.Brush already containing a SolidColorBrush
                (drw.Brush as SolidColorBrush).Color =
                    (drw.Brush as SolidColorBrush).Color == Colors.LightGoldenrodYellow ?
                    Colors.Red : Colors.LightGoldenrodYellow;

                Trace.WriteLine("HitTestCallback: drw.Brush = " + drw.Brush.ToString());

                Trace.WriteLine("HitTestCallback: drw.IsFrozen = " + drw.IsFrozen.ToString());
                Trace.WriteLine("HitTestCallback: drw.Brush.IsFrozen = " + drw.Brush.IsFrozen.ToString());

            }
        }


    }

为了记录，我引用了构造 DrawingVisual 的代码并放入 VisualHostClass

        PathGeometry pgnGeom = RenderPolygonWithHoles2Geometry(pgn);

        DrawingVisual dv = new DrawingVisual();

        using (DrawingContext dc = dv.RenderOpen())
        {
            SolidColorBrush brush1 = new SolidColorBrush(Colors.LightGoldenrodYellow);
            dc.DrawGeometry(brush1, null, pgnGeom);
        }

        myVisualHost.AddVisual(dv);

Answer 1

看来 dc.DrawGeometry(...) 创建的绘图已冻结，即不可修改。

传递我自己的绘图对我有用：

using (var dc = dv.RenderOpen())
{
    dc.DrawDrawing(new GeometryDrawing(Brushes.LightGoldenrodYellow, null, pgnGeom));
}

如何在 MouseHit 上更改 DrawingVisual 的颜色

How to change color of a DrawingVisual on MouseHit

wpf

wpf-graphics