C# - 委托与事件
什么是委托
委托（delegate）
自己不动手，而是交代给别人替你去完成。- 委托就是方法指针，仅仅指向方法的名称，不表示具体执行过程。
- 方法指针是一种数据类型，它所处理的是方法引用过程的类型。
- 委托必须与被委托的方法“类型兼容”。
实例
namespace HelloWorld
{
//委托delegate
public delegate void PhotoFilterHandler(Photo photo);
public class PhotoProcessor
{
public void Process(Photo photo, PhotoFilterHandler filterHandler)
{
//委托delegate传值
filterHandler(photo);
photo.Save();
}
}
}
实例2 —— 多播委托Multicast
using System;
using System.Text;
using static HelloWorld.PhotoProcessor;
namespace HelloWorld
{
class Program
{
static void RedEyesRemovalFilter(Photo photo)
{
Console.WriteLine("去除红颜");
}
static void Main(string[] args)
{
var photo = Photo.load("phtot.jpg");
var filters = new PhotoFilters();
PhotoFilterHandler filterHandler = filters.ApplyBrightness;
//多播委托 Multicast
filterHandler += filters.ApplyContrast;
filterHandler += filters.Resize;
filterHandler += RedEyesRemovalFilter;
var processor = new PhotoProcessor();
processor.Process(photo, filterHandler);
Console.Read();
}
}
}
预定义委托方法Func、Action
System.Action<> 没有返回值
实例
using System;
using System.Text;
namespace HelloWorld
{
class Program
{
static void Main(string[] args)
{
var photo = Photo.load("photo.jpg");
var processor = new PhotoProcessor();
var filters = new PhotoFilters();
// System.Action<> 没有返回值
Action<Photo> filterHandler = filters.ApplyBrightness;
filterHandler += filters.ApplyContrast;
filterHandler += filters.Resize;
filterHandler += RemoveRedEyesFilter;
processor.Process(photo, filterHandler);
Console.Read();
}
static void RemoveRedEyesFilter(Photo photo)
{
Console.WriteLine("去除红眼");
}
}
}
实例2
using System;
namespace HelloWorld
{
// System.Action<> 没有返回值
// System.Func<>有返回值
public class PhotoProcessor
{
// System.Action
public void Process(Photo photo, Action<Photo> filterHandler)
{
filterHandler(photo);
photo.Save();
}
}
}
System.Func<> 有返回值
C#预定义事件
数据、操作、以及通知
实例（闹钟）
using System;
using System.Timers;
using Timer = System.Timers.Timer;
namespace HelloWorld
{
public class Alex
{
internal void AlarmEventHandler(object sender, ElapsedEventArgs e)
{
Console.WriteLine("闹钟响了, 我不管");
}
}
public class RoomMate
{
public int RageValue { get; set; }
internal void AlarmEventHandler(object sender, ElapsedEventArgs e)
{
RageValue += 25;
if (RageValue >= 100)
{
Console.WriteLine("受不了了");
((Timer)sender).Stop();
}
Console.WriteLine("闹钟响了, 我也不管");
}
}
class Program
{
static void Main(string[] args)
{
Timer timer = new Timer();
timer.Interval = 1000;
var alex = new Alex();
var roomMate = new RoomMate();
timer.Elapsed += alex.AlarmEventHandler;
timer.Elapsed += roomMate.AlarmEventHandler;
timer.Start();
Console.Read();
}
}
}
自定义事件
event-in-general，事件的完整声明
实例
OrderProcessor.cs
using System;
using System.Collections.Generic;
namespace HelloWord
{
//EventArgs是包含事件数据的类的基类，用于传递事件的细节
public class OrderProcessorEventArgs : EventArgs
{
public string Status { get; set; }
public DateTime ProcessingTime { get; set; }
public string Desctiption { get; set; }
}
//声明委托delegate
//EventHandler
//传入的两个参数 Order order, OrderProcessorEventArgs args
public delegate void OrderProcessorEventHandler(Order order, OrderProcessorEventArgs args);
public class OrderProcessor
{
//事件约束
private OrderProcessorEventHandler _orderProcessorEventHandler;
public event OrderProcessorEventHandler OrderProcessorEvent
{
add
{
this._orderProcessorEventHandler += value;
}
remove
{
this._orderProcessorEventHandler -= value;
}
}
public void Process(Order order)
{
// 订单处理...
// 订单处理完成，发送订单处理完成事件
if (_orderProcessorEventHandler != null)
{
var e = new OrderProcessorEventArgs
{
Status = "completed",
ProcessingTime = DateTime.UtcNow,
Desctiption = "处理得非常成功"
};
_orderProcessorEventHandler(order, e);
}
}
}
}
Program.cs
using System;
using System.Collections;
using System.Collections.Generic;
namespace HelloWord
{
class Program
{
static void Main(string[] args)
{
var order = new Order
{
Id = 123,
DatePlaced = DateTime.Now,
TotalPrice = 30f
};
OrderProcessor orderProcessor = new OrderProcessor();
//事件的订阅 和 处理
orderProcessor.OrderProcessorEvent += SmsMessageService.OnOrderProcessed;
orderProcessor.OrderProcessorEvent += MailService.OnOrderProcessed;
orderProcessor.Process(order);
Console.Read();
}
}
}
MailService.cs（事件响应者）
using System;
namespace HelloWord
{
internal class MailService
{
internal static void OnOrderProcessed(Order order, OrderProcessorEventArgs args)
{
Console.WriteLine($"发送邮件，订单 {order.Id} , 处理结果: {args.Status}, 处理时间: {args.ProcessingTime}");
}
}
}
SmsMessageService.cs（事件响应者）
using System;
namespace HelloWord
{
public class SmsMessageService
{
internal static void OnOrderProcessed(Order order, OrderProcessorEventArgs args)
{
Console.WriteLine($"发送短信，订单 {order.Id} , 处理结果: {args.Status}, 处理时间: {args.ProcessingTime}");
}
}
}
Order.cs
using System;
namespace HelloWord
{
public class Order
{
public int Id { get; set; }
public DateTime DatePlaced { get; set; }
public float TotalPrice { get; set; }
public bool IsShipped { get; set; }
}
}
测试
field-like，字段式声明（下一节）
字段式事件声明（field-like）
field-like，字段式声明
实例
OrderProcessor.cs
using System;
using System.Collections.Generic;
namespace HelloWord
{
public class OrderProcessorEventArgs : EventArgs
{
public string Status { get; set; }
public DateTime ProcessingTime { get; set; }
public string Desctiption { get; set; }
}
public class OrderProcessor
{
//预定义事件 EventHandler
public event EventHandler<OrderProcessorEventArgs> OrderProcessorEvent;
public void Process(Order order)
{
// 订单处理...
// 订单处理完成，发送订单处理完成事件
if (OrderProcessorEvent != null)
{
var e = new OrderProcessorEventArgs
{
Status = "completed",
ProcessingTime = DateTime.UtcNow,
Desctiption = "处理得非常成功"
};
OrderProcessorEvent(order, e);
}
}
}
}
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