如何刪除動態創建的事件處理程序？

Question

我是新手。 我認為這個問題很簡單，但是找不到解決方案。 單擊button1將打開一個彈出窗口，並向canvas1添加MouseDown事件處理程序canvas1.MouseDown += (s1, e1) =>{...}; 我想在用戶關閉彈出窗口時刪除它。 這是整個代碼：

namespace MyfApplication1
{
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();

            int linesNumber = 0;

            Button button1 = new Button();
            button1.Content = "Draw";
            button1.HorizontalAlignment = HorizontalAlignment.Left;
            button1.VerticalAlignment = VerticalAlignment.Top;
            button1.Click += (s, e) =>
            {
                Popup popup = new Popup();
                popup.PlacementTarget = button1;
                popup.IsOpen = true;

                Button closePopupButton = new Button();
                closePopupButton.Content = "close";
                closePopupButton.Click += (s1, e1) =>
                {
                    popup.IsOpen = false;
                    // remove canvas1.MouseDown event handler here
                };
                popup.Child = closePopupButton;

                canvas1.MouseDown += (s1, e1) =>
                {
                    Point point = Mouse.GetPosition(canvas1);
                    Line line = new Line();
                    line.X2 = point.X; line.Y2 = point.Y;
                    line.Stroke = Brushes.Red; line.StrokeThickness = 1;
                    canvas1.Children.Add(line);
                    linesNumber++;
                };
            };
            grid1.Children.Add(button1);
        }
    }
}

Answer 1

將事件處理程序保存在變量中的某個位置

MouseButtonEventHandler onMousedown = (o, args) => 
{ 
    ...
};

canvas1.MouseDown += onMouseDown;

然后您可以再次刪除事件處理程序：

canvas1.MouseDown -= onMouseDown;