Question

我正在制作一个workflowdesigner，用wpf和vb.net在画布上创建工作流程。我已经可以在具有良好功能的对象之间绘制线条（关系）。现在我想实现一种删除关系的方法。我在形状上添加了一个onclick处理程序，但该行非常薄且难以点击。我听说画了2行1，行程厚度较粗，但这是不可能的，因为画线方法在cpu上很重。

感谢您的帮助

大卫

Answer 1

您可以将鼠标按下事件处理程序添加到Canvas而不是Shape对象，然后使用Hit Testing in the Visual Layer执行hit test geometry（尽管API有点奇怪），例如椭圆。 Canvas需要设置Background（例如Transparent}才能接收鼠标事件。

很抱歉这是C＃，但我不会说VB：

private void Canvas_MouseLeftButtonDown(object sender, MouseButtonEventArgs e)
{
    Canvas canvas = sender as Canvas;
    EllipseGeometry hitTestGeometry =
        new EllipseGeometry(e.GetPosition(canvas), 10d, 10d);
    Shape hitShape = null;

    HitTestResultCallback hitTestCallback =
        result =>
        {
            hitShape = result.VisualHit as Shape;
            return hitShape != null ? HitTestResultBehavior.Stop : HitTestResultBehavior.Continue;
        };

    VisualTreeHelper.HitTest(canvas, null, hitTestCallback, new GeometryHitTestParameters(hitTestGeometry));

    if (hitShape != null)
    {
        System.Diagnostics.Trace.TraceInformation("hit shape: {0}", hitShape);
    }
}

修改

这是等效的VB代码。 VB不支持多行lambda表达式，因此必须明确声明命中测试回调

Private Function htCallback(ByVal result As HitTestResult) _ As HitTestResultBehavior Dim hitShape As Shape = Nothing hitShape = TryCast(result.VisualHit, Shape) If hitShape IsNot Nothing Then 'do something End If Return If(hitShape IsNot Nothing, HitTestResultBehavior.[Stop], _ HitTestResultBehavior.[Continue]) End Function Private Sub Canvas_MouseLeftButtonDown(ByVal sender As Object, _ ByVal e As MouseButtonEventArgs) Handles Canvas1.MouseRightButtonDown Dim canvas As Canvas = TryCast(sender, Canvas) Dim hitTestGeometry As New EllipseGeometry(e.GetPosition(canvas), 10.0, 10.0) Dim hitTestCallback As HitTestResultCallback = _ New HitTestResultCallback(AddressOf htCallback) VisualTreeHelper.HitTest(canvas, Nothing, hitTestCallback, _ New GeometryHitTestParameters(hitTestGeometry)) End Sub

Answer 2

也许是一个简单的答案，但是当您将新行添加到画布时，您可以执行类似

的操作

AddHandler myLine.MouseEnter, AddressOf lineHover
AddHandler myLine.MouseLeave, AddressOf lineLeave
AddHandler myLine.MouseDown, AddressOf lineDelete
Canvas1.Children.Add(myLine)

其中

Private Sub lineHover(ByVal sender As Object, ByVal e As MouseEventArgs)
    CType(sender, Line).StrokeThickness = 3
End Sub

Private Sub lineLeave(ByVal sender As Object, ByVal e As MouseEventArgs)
    CType(sender, Line).StrokeThickness = 1
End Sub

Private Sub lineDelete(ByVal sender As Object, ByVal e As MouseEventArgs)
    Canvas1.Children.Remove(CType(sender, Line))
End Sub

这样当你的鼠标悬停在一条线上时，它的笔触粗细就会增加。这使得该行更容易点击，并且还为您的用户提供了关于他们删除哪一行的一些很好的反馈。

工作流程设计师线条太酷了

2 个答案: