逆变性

只要函数参数与委托兼容，就能创建委托实例。

 1 Button button = new Button(); 2 //public delegate void EventHandler(object sender, EventArgs e); 3 button.Click += LogPlainEvent; 4 //public delegate void KeyPressEventHandler(object sender, KeyPressEventArgs e); 5 button.KeyPress += LogPlainEvent; 6 //public delegate void MouseEventHandler(object sender, MouseEventArgs e); 7 button.MouseClick += LogPlainEvent; 8  9 public void LogPlainEvent(object sender, EventArgs e)10 {11 }

协变性

只要返回值类型与委托兼容，就能创建委托实例

 1 public delegate Stream StreamFactory(); 2  3 public MemoryStream GenerateData() 4 { 5 return new MemoryStream(); 6 } 7  8 StreamFactory factory = GenerateData; 9 using (Stream stream = factory())10 {11 int data;12 while((data = stream.ReadByte()) != -1)13  {14  Console.WriteLine(data);15  }16 }