C# 实例解析事件委托之EventHandler

Posted 2022-12-14 dotNET跨平台

概述

     事件属于委托的一个子集，像我们平时界面上的鼠标点击按钮后响应事件、事件的发布和订阅等都需要用到委托.通过委托可以很好的实现类之间的解耦好。事件委托EventHandler的

函数原型如下：delegate 表示这个个委托，事件委托没有返回值，有两个入参，sender是事件触发的对象，e是一个泛型的事件类型参数

public delegate void EventHandler<TEventArgs>(object sender, TEventArgs e);

用法举例

用法举例1：窗体关闭事件

public void Cancel(object obj, bool e)
        
            if (e)
            
                sw.AppendLine("try clsoe window");
            
            else
            
                sw.AppendLine("clsoe window is cancel");
            
        

//事件委托1，事件是委托的子集
            EventHandler<bool> windowTryClose = Cancel;
            windowTryClose(this, false);

这里在定义了一个委托EventHandler<bool>，将方法Cancel委托给他，然后嗲用委托执行。

注意：EventHandler<bool> windowTryClose = Cancel;是
EventHandler<bool> windowTryClose = new EventHandler<bool>(Cancel);的简写

传入的参数是false，所以运行结果：

clsoe window is cancel

用法举例2 ：按钮点击事件

//事件委托2
            Button button = new Button();
            button.ClickEvent += Button_Click;
            button.ClickAction();

public void Button_Click(Object sender, EventArgs args)
        
            sw.AppendLine("这是按钮点击事件");
        

public class Button
    
        public EventHandler ClickEvent;
        public void ClickAction()
        
            ClickEvent.Invoke(this, new EventArgs());
        
    

这里主要是写了按钮点击事件的一个委托，一般在定义事件委托时前面可以用event去修饰，我这里省略了，

用法举例3 ：事件发布与订阅

//事件委托3
            var myPublishEventArgs = new PublishEvent();
            _ = new SubscribeEvent(myPublishEventArgs);
            myPublishEventArgs.Publish();

public class MyPublishEventArgs : EventArgs
    
        public string InfoString  get; set; 
    


    public class PublishEvent
    
        public event EventHandler<MyPublishEventArgs> OnPublish;
        public void Publish()
        
            OnPublish?.Invoke(this, new MyPublishEventArgs()  InfoString = "hello" );
        
    


    public class SubscribeEvent
    
        public SubscribeEvent(PublishEvent publishEvent)
        
            publishEvent.OnPublish += Subscribe;
        
        public void Subscribe(Object sender, MyPublishEventArgs args)
        
            MessageBox.Show($"我接收到的消息是:args.InfoString");
        
    

这里封装了几个类，MyPublishEventArgs是我要发送的事件，MyPublishEventArgs这个类是发布者，SubscribeEvent这个是订阅者，主要订阅事件一定要放在发布前，这样才能成功接收到事件.

委托部分这里就讲解完事了，全部源码如下：

using PropertyChanged;
using System;
using System.Text;
using System.Threading;
using System.Windows;


namespace Caliburn.Micro.Hello.ViewModels

    [AddINotifyPropertyChangedInterface]
    public class DelegateViewModel : Screen,IViewModel
    
        public string ResultString  get; set; 
        delegate int DelegateM(string a, string b);//声明,可以有返回值也可以没有
        StringBuilder sw = new StringBuilder();


        public DelegateViewModel()
        
            DisplayName = "DelegateTest";
        


        public void Test()
        
            sw.AppendLine($"【Delegate测试】执行线程id:Thread.CurrentThread.ManagedThreadId");


            //func用法1
            //Func<string, string, int> func = new Func<string, string, int>(p.StringAddA);
            Func<string, string, int> func = StringAddA;//简写
            var result = func.Invoke("3", "5");//可以简化为func("3", "5")
            sw.AppendLine($"【func用法1】func返回结果是:result");


            //func用法2，用lamda表达式简化写法,通过+=注册实现多播委托
            func += (a, b) =>
            
                return int.Parse(a) - int.Parse(b);
            ;
            sw.AppendLine($"【func用法2】func返回结果是:func("3", "5")");


            //Action用法
            //Action<string, string> action = new Action<string, string>(p.StringAddB);
            Action<string, string> action = StringAddB;//简写
            IAsyncResult asyncResult = action.BeginInvoke("3", "5", null, null);//action("3", "5"),BeginInvoke异步执行，即：开启新现成处理StringAddB
            action.EndInvoke(asyncResult);//阻塞委托，直到执行完成
            if (asyncResult.IsCompleted)
            
                sw.AppendLine($"【Action用法】当前异步委托线程已执行完成");
            


            Test(func, action);//将方法委托后转化为参数进行传递


            //delegate用法
            //DelegateM delegateM = new DelegateM(p.StringAddA);
            DelegateM delegateM = StringAddA;//简写
            sw.AppendLine($"【delegate用法】delegate返回结果是:delegateM("3", "5")");


            //事件委托1，事件是委托的子集
            EventHandler<bool> windowTryClose = new EventHandler<bool>(Cancel);
            windowTryClose(this, false);


            //事件委托2
            Button button = new Button();
            button.ClickEvent += Button_Click;
            button.ClickAction();


            //事件委托3
            var myPublishEventArgs = new PublishEvent();
            _ = new SubscribeEvent(myPublishEventArgs);
            myPublishEventArgs.Publish();


            ResultString = sw.ToString();
        


        public int StringAddA(string a, string b)
        
            return int.Parse(a) + int.Parse(b);
        


        public void StringAddB(string a, string b)
        
            sw.AppendLine($"【Action用法】Action执行线程id:Thread.CurrentThread.ManagedThreadId");
            sw.AppendLine($"【Action用法】Action执行结果:(int.Parse(a) + int.Parse(b))");
        


        public void Test(Func<string, string, int> f, Action<string, string> a)
        
            a.Invoke(f.Invoke("3", "5").ToString(), "5");
        


        public void Cancel(object obj, bool e)
        
            if (e)
            
                sw.AppendLine("try clsoe window");
            
            else
            
                sw.AppendLine("clsoe window is cancel");
            
        


        public void Button_Click(Object sender, EventArgs args)
        
            sw.AppendLine("这是按钮点击事件");
        


        public void MyEvent(Object sender, EventArgs args)
        
            sw.AppendLine("这是按钮点击事件");
        
    


    public class Button
    
        public EventHandler ClickEvent;
        public void ClickAction()
        
            ClickEvent.Invoke(this, new EventArgs());
        
    


    public class MyPublishEventArgs : EventArgs
    
        public string InfoString  get; set; 
    


    public class PublishEvent
    
        public event EventHandler<MyPublishEventArgs> OnPublish;
        public void Publish()
        
            OnPublish?.Invoke(this, new MyPublishEventArgs()  InfoString = "hello" );
        
    


    public class SubscribeEvent
    
        public SubscribeEvent(PublishEvent publishEvent)
        
            publishEvent.OnPublish += Subscribe;
        
        public void Subscribe(Object sender, MyPublishEventArgs args)
        
            MessageBox.Show($"我接收到的消息是:args.InfoString");
        
    

运行结果：