Question

我正在创建一个项目，我用Visual Studio上的C＃创建整个项目（包括模板）。

我已经制作了模板并且刚刚开始处理事件，我想为我创建的Canvas创建一个事件MouseLeftButtonDown，此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);

        }

这是我的活动：

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

我试过down1 = e.GetPosition(canvas1);，但我在（canvas1）上收到错误; “名称canvas1在当前上下文中不存在”

我做了一个类似的项目，无需编写模板，没有任何问题..

Answer 1

但我在（canvas1）上遇到错误;

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

您可以使用：

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

Answer 2

您在Grid1_Loaded方法中将canvas1声明为局部变量。将它在类中定义为成员变量，它应该可以工作。

Answer 3

怎么样：

down1 = e.GetPosition((Canvas)sender);

Answer 4

问题是canvas1是Grid1_Loaded中的局部变量。无法在该方法之外访问该变量。

Answer 5

问题是canvas1不在范围内。你可以像这样内联一个简单的lambda表达式：

canvas1.MouseLeftButtonDown += (sender, e) => down1 = e.GetPosition(canvas1);

为什么我无法从事件处理程序中访问变量？

5 个答案: