WPF:在文本块的顶部绘制
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29-09-2019 - |
题
我希望能够利用文本块的顶部,并找到了一种方法,但是一旦图纸就无法删除。这是代码。
public class DerivedTextBlock : TextBlock {
public Boolean DrawExtra {
get { return (Boolean)GetValue(DrawExtraProperty); }
set { SetValue(DrawExtraProperty, value); }
}
// Using a DependencyProperty as the backing store for DrawExtra. This enables animation, styling, binding, etc...
public static readonly DependencyProperty DrawExtraProperty =
DependencyProperty.Register("DrawExtra", typeof(Boolean), typeof(DerivedTextBlock), new FrameworkPropertyMetadata(false, FrameworkPropertyMetadataOptions.AffectsRender | FrameworkPropertyMetadataOptions.AffectsArrange));
public DrawingVisual DrawingVisual { get; set; }
public DerivedTextBlock() {
DrawingVisual = this.CreateDrawingVisualRectangle();
}
protected override int VisualChildrenCount {
get {
//if we want to draw our extra info, add one to
// our visualChildrenCount, usually with a textblock it is 0
if (DrawExtra) {
return base.VisualChildrenCount + 1;
}
else {
return base.VisualChildrenCount;
}
}
}
protected override Visual GetVisualChild(int index) {
return DrawingVisual;
}
// Create a DrawingVisual that contains a rectangle.
private DrawingVisual CreateDrawingVisualRectangle() {
DrawingVisual drawingVisual = new DrawingVisual();
// Retrieve the DrawingContext in order to create new drawing content.
DrawingContext drawingContext = drawingVisual.RenderOpen();
// Create a rectangle and draw it in the DrawingContext.
Rect rect = new Rect(new Point(10.0, 0), new Size(10.0 / 2.0, 10));
drawingContext.DrawRectangle(Brushes.LightBlue, (Pen)null, rect);
// Persist the drawing content.
drawingContext.Close();
return drawingVisual;
}
}
我要这样做的原因:我们有一个带有许多单元格的数据,每个单元格显示了文本。我们在单元格上显示了一些验证信息,并通过使用带有文本块的模板和网格中的一些hosten路径来执行此操作。它的开销为视觉树增添了额外的元素,当我们必须重新绘制(在加载,切换窗口或某种方面)时,它需要更长的时间,而视觉树中的元素越多。当它只是一个文本块时,它比拥有网格的控件快于1/3-1/2。因此,我们想在文本框顶部绘制验证内容。
解决方案
您的问题是:
- getVisualChild()应返回base.getVisualChild(index),除非index == base.visualChildRencount。
- 您忘了在DrawsExtra变为true或DrawsVisual更改时忘记调用AddVisualChild()
- 您忘了调用dracterextra变为false或drausthvisual更改时调用removevisualChild()
您可以通过在DrawingExtra上设置属性ChangedCallback并将代码添加到DrawsVisual的设置中来修复#2和#3。
说明:实际上将视觉添加到树上的是AddVisualChild()调用。发生的事情是,由于您在getVisualChild()中的错误,您的视觉效果被发现并显示出“偶然”,但是它没有正确地链接到视觉树中,因此您会遇到许多问题。
更新
我如上所述编辑了您的代码,并且效果很好。这是更改:
...
{
PropertyChangedCallback = (obj, e) =>
{
var textBlock = (DerivedTextBlock)obj;
if((bool)e.OldValue) textBlock.RemoveVisualChild(textBlock.DrawingVisual);
if((bool)e.NewValue) textBlock.AddVisualChild(textBlock.DrawingVisual);
}
});
public DrawingVisual DrawingVisual
{
get { return _drawingVisual; }
set
{
if(DrawExtra) RemoveVisualChild(_drawingVisual);
_drawingVisual = value;
if(DrawExtra) AddVisualChild(_drawingVisual);
}
}
private DrawingVisual _drawingVisual;
...
protected override int VisualChildrenCount
{
get { return base.VisualChildrenCount + (DrawExtra ? 1 : 0); }
}
protected override Visual GetVisualChild(int index)
{
return index==base.VisualChildrenCount ? DrawingVisual : base.GetVisualChild(index);
}
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