发布基于 EventHandler 模式的事件
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2022-05-27 23:46:25
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一、随事件一起发送自定义数据且不使用泛型
1、如果随事件一起发送自定义数据,将自定义数据的类声明为对发布服务器和订阅者类均可见的范围。 然后添加所需成员以保留自定义事件数据。 在此示例中,将返回一个简单的字符串。
public class CustomEventArgs : EventArgs { public CustomEventArgs(string s) { msg = s; } private string msg; public string Message { get { return msg; } } }
2、声明发布类中的委托。 为以 EventHandler 结尾的委托命名。 第二个参数指定自定义 EventArgs 类型。
public delegate void CustomEventHandler(object sender, CustomEventArgs a);
3、定义事件,将委托声明为类型。
public event CustomEventHandler RaiseCustomEvent;
二、如果不随事件发送自定义数据。
如果没有任何自定义 EventArgs 类,事件类型将为非泛型 EventHandler 委托。 你无需声明该委托,因为它已在创建 C# 项目时包括的 System 命名空间中声明。 将以下代码添加到发布服务器类。
public event EventHandler RaiseCustomEvent;
三、随事件一起发送自定义数据且使用泛型。
则无需自定义委托。 而是在发布类中,将事件类型指定为 EventHandler<CustomEventArgs>
,替换尖括号中自定义类的名称。
public event EventHandler<CustomEventArgs> RaiseCustomEvent;
示例
下例通过使用自定义 EventArgs 类和 EventHandler<TEventArgs> 作为事件类型来演示之前的步骤。
namespace DotNetEvents { using System; using System.Collections.Generic; // Define a class to hold custom event info public class CustomEventArgs : EventArgs { public CustomEventArgs(string s) { message = s; } private string message; public string Message { get { return message; } set { message = value; } } } // Class that publishes an event class Publisher { // Declare the event using EventHandler<T> public event EventHandler<CustomEventArgs> RaiseCustomEvent; public void DoSomething() { // Write some code that does something useful here // then raise the event. You can also raise an event // before you execute a block of code. OnRaiseCustomEvent(new CustomEventArgs("Did something")); } // Wrap event invocations inside a protected virtual method // to allow derived classes to override the event invocation behavior protected virtual void OnRaiseCustomEvent(CustomEventArgs e) { // Make a temporary copy of the event to avoid possibility of // a race condition if the last subscriber unsubscribes // immediately after the null check and before the event is raised. EventHandler<CustomEventArgs> handler = RaiseCustomEvent; // Event will be null if there are no subscribers if (handler != null) { // Format the string to send inside the CustomEventArgs parameter e.Message += $" at {DateTime.Now}"; // Use the () operator to raise the event. handler(this, e); } } } //Class that subscribes to an event class Subscriber { private string id; public Subscriber(string ID, Publisher pub) { id = ID; // Subscribe to the event using C# 2.0 syntax pub.RaiseCustomEvent += HandleCustomEvent; } // Define what actions to take when the event is raised. void HandleCustomEvent(object sender, CustomEventArgs e) { Console.WriteLine(id + " received this message: {0}", e.Message); } } class Program { static void Main(string[] args) { Publisher pub = new Publisher(); Subscriber sub1 = new Subscriber("sub1", pub); Subscriber sub2 = new Subscriber("sub2", pub); // Call the method that raises the event. pub.DoSomething(); // Keep the console window open Console.WriteLine("Press Enter to close this window."); Console.ReadLine(); } } }
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