繪制矩形並在每次鼠標點擊時更新它

Question

現在我想在鼠標單擊事件上在畫布上繪制一個矩形。 這是我的代碼：

    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;
    }

每次單擊鼠標時它都能正常工作，但是為什么當我重新繪制新矩形時，舊矩形仍在畫布上？ 我做錯了什么？

編輯現在是正確的，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

您正在致電：

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

然后：

canvas1.Children.Add(rect);

這會將另一個新的Rectangle添加到您的Canvas.Children集合中。 如果您想先刪除舊的，請先調用：

canvas1.Children.Remove(rect);