绘制矩形并在每次鼠标点击时更新它

Question

现在我想在鼠标单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;
    }

每次单击鼠标时它都能正常工作，但是为什么当我重新绘制新矩形时，旧矩形仍在画布上？ 我做错了什么？

编辑现在是正确的，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);

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

canvas1.Children.Remove(rect);