数据结构
网络
关系数据库管理系统 (RDBMS)
操作系统
Java
MS Excel
iOS
HTML
CSS
Android
Python
C语言编程
C++
C#
MongoDB
MySQL
Javascript
PHP
物理学
化学
生物学
数学
英语
经济学
心理学
社会学
服装设计
法学.NET中的事件模式是如何工作的？
事件是一种使用委托的简化模式。在C#中，所有委托都具有多播能力，即委托的实例不仅可以表示单个方法，还可以表示方法列表。例如：
示例
delegate int Transformer(int x);
static void Main(){
Transformer perform = x =>{
int result = x * x;
Console.WriteLine(result);
return result;
};
perform += x =>{
int result = x * x * x;
Console.WriteLine(result);
return result;
};
perform(2); // prints 4 and 8
}调用Perform()会调用添加到委托中的所有方法。方法按照添加的顺序调用。
这允许你实现发布-订阅模式，也称为事件模式。发布者包含一个委托字段。它决定何时通过调用委托来发布。订阅者将自己的方法添加到发布者的委托中，因此每当发布者决定通过调用委托来发布时，它们都会收到通知。订阅者不知道也不干涉其他订阅者。
C#事件是一种语言特性，它以类型安全的方式规范了上述模式，从而避免了委托的常见错误。事件公开实现事件模式所需的委托功能的子集。下面的示例对此进行了说明。
首先，定义事件发生时要发送的数据结构。
public class ThresholdReachedEventArgs : EventArgs{
public int Threshold { get; set; }
public DateTime TimeReached { get; set; }
}然后，定义发布者，即想要引发事件的类。
public class Counter{
// 1. Define an event
public event EventHandler<ThresholdReachedEventArgs> ThresholdReached;
// 2. Do something that raises the event, and pass the EventArgs custom data
public void DoSomething(){
ThresholdReachedEventArgs e = new ThresholdReachedEventArgs{
Threshold = 10,
TimeReached = DateTime.Now
};
// 3. Raise the actual event
ThresholdReached?.Invoke(this, e);
}
}最后，创建一个或多个订阅者。想要监听发布者引发的事件的类。
class Program{
static void Main(string[] args){
// 1. Create an instance of the publisher, which you want to listen to
Counter counter = new Counter();
// 2. Attach an event handler on the publisher
counter.ThresholdReached += OnThresholdReached;
// 3. Do something that will raise the event. Now you are ready to listen to the event.
counter.DoSomething();
}
// 4. Handle the event which is raised by publisher
static void OnThresholdReached(object sender, ThresholdReachedEventArgs e){
Console.WriteLine($"Reached Threshold {e.Threshold} at {e.TimeReached.ToString()}");
}
}示例
using System;
class Program{
static void Main(string[] args){
// 1. Create an instance of the publisher, which you want to listen to
Counter counter = new Counter();
// 2. Attach an event handler on the publisher
counter.ThresholdReached += OnThresholdReached;
// 3. Do something that will raise the event. Now you are ready to listen to the event.
counter.DoSomething();
}
// 4. Handle the event which is raised by publisher
static void OnThresholdReached(object sender, ThresholdReachedEventArgs e){
Console.WriteLine($"Reached Threshold {e.Threshold} at {e.TimeReached.ToString()}");
}
}
public class ThresholdReachedEventArgs : EventArgs{
public int Threshold { get; set; }
public DateTime TimeReached { get; set; }
}
public class Counter{
// 1. Define an event
public event EventHandler<ThresholdReachedEventArgs> ThresholdReached;
// 2. Do something that raises the event, and pass the EventArgs custom data
public void DoSomething(){
ThresholdReachedEventArgs e = new ThresholdReachedEventArgs{
Threshold = 10,
TimeReached = DateTime.Now
};
// 3. Raise the actual event
ThresholdReached?.Invoke(this, e);
}
}输出
Reached Threshold 10 at 5/15/2021 12:49:10 PM
更新于：2021年5月19日
475 次浏览
广告