Question

现在我想在鼠标点击事件上在画布上绘制一个矩形。这是我的代码：

    protected void imageIR_MouseClick(object sender, System.Windows.Input.MouseEventArgs e)
    {
    ...
        System.Windows.Point startPoint = e.GetPosition(canvas1);
        rect = new System.Windows.Shapes.Rectangle
        {
            Stroke = System.Windows.Media.Brushes.LightBlue,
            StrokeThickness = 10
        };
        Canvas.SetLeft(rect, startPoint.X);
        Canvas.SetTop(rect, startPoint.Y);
        canvas1.Children.Add(rect);
    }

    private void Canvas_MouseMove(object sender, System.Windows.Input.MouseEventArgs e)
    {
        rect = null;
    }

每次点击鼠标都可以正常工作，但是当我重新绘制新鼠标时，为什么旧的矩形仍然在画布上？我做错了什么？

编辑现在它是正确的，我不再需要Canvas_MouseMove而是：

    protected void imageIR_MouseClick(object sender, System.Windows.Input.MouseEventArgs e)
    {
    ...
        canvas1.Children.Remove(rect);
        System.Windows.Point startPoint = e.GetPosition(canvas1);
        rect = new System.Windows.Shapes.Rectangle
        {
            Stroke = System.Windows.Media.Brushes.LightBlue,
            StrokeThickness = 10
        };
        Canvas.SetLeft(rect, startPoint.X);
        Canvas.SetTop(rect, startPoint.Y);
        canvas1.Children.Add(rect);
    }

Answer 1

您正在致电：

rect = new System.Windows.Shapes.Rectangle(...);

然后：

canvas1.Children.Add(rect);

将另一个新Rectangle添加到您的Canvas.Children集合中。如果您想先删除旧的，请先调用它：

canvas1.Children.Remove(rect);

绘制矩形并在每次单击鼠标时更新它

1 个答案: