绘制矩形并在每次鼠标单击时更新 [英] Draw rectangle and update it on every mouse click

问题描述

现在我想在画布上绘制一个矩形，鼠标点击事件。这是我的代码：

Now I want to draw a rectangle on canvas on mouse click Event. Here is my code:

    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;
    }

每次点击鼠标时都可以正常工作，在画布上，当我重新绘制一个新的？我错了？

It works fine everytime I clicked the mouse, but why is the old rectangle still on the canvas when I redraw the new one? What I did wrong?

编辑现在是正确的，我不再需要Canvas_MouseMove，而是：

EDIT Now it's correct, I don't Need Canvas_MouseMove anymore and instead:

    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);
    }

推荐答案

p>

You are calling:

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

然后：

canvas1.Children.Add(rect);

这将添加另一个新 Rectangle 添加到您的 Canvas.Children 集合中。如果你想先删除旧的，然后调用这个：

Which will add another new Rectangle into your Canvas.Children collection. If you want to remove the old one first, then call this first:

canvas1.Children.Remove(rect);

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