c# - 为什么我不能从事件处理程序中访问变量？

Question

我正在制作一个项目，我在 Visual Studio 上使用 C# 创建整个项目(包括模板)。

我制作了模板并刚刚开始处理事件，我想为我创建的 Canvas 制作一个事件 MouseLeftButtonDown，该事件将记录鼠标位置。

这是我的代码:

 public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }

        private char tester;
        private Point down1;
        private Point up1;

        private void Grid1_Loaded(object sender, RoutedEventArgs e)
        {
            RowDefinition row1 = new RowDefinition();
            RowDefinition row2 = new RowDefinition();

            row1.Height = new GridLength(40);
            row2.Height = new GridLength(1, GridUnitType.Star);

            Grid1.RowDefinitions.Add(row1);
            Grid1.RowDefinitions.Add(row2);

            Canvas canvas1 = new Canvas();
            canvas1.Background = new SolidColorBrush(Colors.Beige);
            Grid.SetRow(canvas1, 1);
            Grid1.Children.Add(canvas1);
            canvas1.MouseLeftButtonDown += new RoutedEventHandler(canvas1_MouseLeftButtonDown);
            canvas1.MouseLeftButtonUp += new RoutedEventHandler(canvas1_MouseLeftButtonUp);


            Button btnRect = new Button();
            btnRect.Content = "Rectangulo";
            btnRect.Margin = new Thickness(5, 5, 5, 5);
            btnRect.HorizontalAlignment = HorizontalAlignment.Left;
            btnRect.VerticalAlignment = VerticalAlignment.Center;
            Grid.SetRow(btnRect, 0);
            Grid1.Children.Add(btnRect);
            //btnRect.Click += new RoutedEventHandler(btnRect_Click);

            Button btnEllip = new Button();
            btnEllip.Content = "Ellipse";
            btnEllip.Margin = new Thickness(75, 5, 5, 5);
            btnEllip.HorizontalAlignment = HorizontalAlignment.Left;
            btnEllip.VerticalAlignment = VerticalAlignment.Center;
            Grid.SetRow(btnEllip, 0);
            Grid1.Children.Add(btnEllip);
            //btnEllip.Click += new RoutedEventHandler(btnEllip_Click);

        }

这是我的事件:

private void canvas1_MouseLeftButtonDown(object sender, MouseButtonEventArgs e)
            {
                 down1 = e.GetPosition(canvas1); 
            }
        }
    }

我尝试执行 down1 = e.GetPosition(canvas1); 但我在 (canvas1) 上遇到错误； “名称 canvas1 在当前上下文中不存在”

我已经做了一个类似的项目而无需编写模板，没有任何问题..

Answer 1

but I'm getting an error on (canvas1);

那是因为 canvas1 是另一个方法的局部变量，不能在 canvas1_MouseLeftButtonDown() 内部访问。

您可以使用:

 Canvas c = sender as Canvas;  // or Canvas c = (Canvas) sender;
 down1 = e.GetPosition(c);