如何：创建 OnEnter 功能

更新：2007 年 11 月

.NET Compact Framework 不支持控件的 OnEnter 和 OnLeave 方法。但是，由于支持 OnMouseMove 方法，因此可使用该方法和 Capture 属性来确定鼠标指针进入或离开控件的时间。

此示例定义了一个简单的自定义控件 MouseCapture，当在该控件内部移动鼠标时，该控件将变为蓝色；当鼠标移动到它的外面时，将变为浅灰色。该控件使用 OnMouseMove 方法来确定鼠标坐标是否处于 ClientRectangle 范围之内。

请注意，在控件内部和外部点击不会改变其颜色。您必须拖动鼠标来执行诸如拖放的操作。

创建和实现自定义控件

1. 将 MouseCapture 自定义控件添加到项目中。

   Public Class MouseCapture
      Inherits Control
   
      Public Sub New()
         Me.BackColor = Color.LightGray
      End Sub 'New
   
   
      ' If the mouse is over the control, Capture is true. 
      Protected Overrides Sub OnMouseMove(e As MouseEventArgs)
         Me.Capture = Me.ClientRectangle.Contains(e.X, e.Y)
         If Me.Capture Then
            ' Blue indicates inside the control.
            Me.BackColor = Color.Blue
         Else
            Me.BackColor = Color.LightGray
         End If
      End Sub 
   End Class
   

   public class MouseCapture : Control
   {
       public MouseCapture()
       {
           this.BackColor = Color.LightGray;
       }
   
       // If the mouse is over the custom control, Capture is true.
       protected override void OnMouseMove(MouseEventArgs e)
       {
           this.Capture = this.ClientRectangle.Contains(e.X, e.Y);
           if (this.Capture == true)
               this.BackColor = Color.Blue;
           else
               this.BackColor = Color.LightGray;
       }
   }
   

2. 在窗体构造函数中或者为窗体 Load 的事件创建一个 MouseCapture 实例。

   ' Assumes mc has been delared
   ' for the form as type MouseCapture.
     Dim mc As New MouseCapture()
     mc.Parent = Me
     mc.Bounds = New Rectangle(20, 50, 100, 50)
   

   // Assumes mc has been delared
   // for the form as type MouseCapture.
   mc = new MouseCapture();
   mc.Parent = this;
   mc.Bounds = new Rectangle(20, 50, 100, 50);
   

编译代码

此示例需要引用下面的命名空间：

• System

• System.Drawing

• System.Windows.Forms

请参见

概念

自定义控件开发

.NET Compact Framework 帮助主题