如何在 C# 中创建自己的事件？

How can I make my own event in C#?

提问by Gold

How can I make my own event in C#?

如何在 C# 中创建自己的事件？

采纳答案by Gary Willoughby

Here's an example of creating and using an event with C#

这是使用 C# 创建和使用事件的示例

using System;

namespace Event_Example
{
    //First we have to define a delegate that acts as a signature for the
    //function that is ultimately called when the event is triggered.
    //You will notice that the second parameter is of MyEventArgs type.
    //This object will contain information about the triggered event.
    public delegate void MyEventHandler(object source, MyEventArgs e);

    //This is a class which describes the event to the class that recieves it.
    //An EventArgs class must always derive from System.EventArgs.
    public class MyEventArgs : EventArgs
    {
        private string EventInfo;
        public MyEventArgs(string Text)
        {
            EventInfo = Text;
        }
        public string GetInfo()
        {
            return EventInfo;
        }
    }

    //This next class is the one which contains an event and triggers it
    //once an action is performed. For example, lets trigger this event
    //once a variable is incremented over a particular value. Notice the
    //event uses the MyEventHandler delegate to create a signature
    //for the called function.
    public class MyClass
    {
        public event MyEventHandler OnMaximum;
        private int i;
        private int Maximum = 10;
        public int MyValue
        {
            get
            {
                return i;
            }
            set
            {
                if(value <= Maximum)
                {
                    i = value;
                }
                else
                {
                    //To make sure we only trigger the event if a handler is present
                    //we check the event to make sure it's not null.
                    if(OnMaximum != null)
                    {
                        OnMaximum(this, new MyEventArgs("You've entered " +
                            value.ToString() +
                            ", but the maximum is " +
                            Maximum.ToString()));
                    }
                }
            }
        }
    }

    class Program
    {
        //This is the actual method that will be assigned to the event handler
        //within the above class. This is where we perform an action once the
        //event has been triggered.
        static void MaximumReached(object source, MyEventArgs e)
        {
            Console.WriteLine(e.GetInfo());
        }

        static void Main(string[] args)
        {
            //Now lets test the event contained in the above class.
            MyClass MyObject = new MyClass();
            MyObject.OnMaximum += new MyEventHandler(MaximumReached);

            for(int x = 0; x <= 15; x++)
            {
                MyObject.MyValue = x;
            }

            Console.ReadLine();
        }
    }
}

回答by Brann

You can declare an event with the following code:

您可以使用以下代码声明事件：

public event EventHandler MyOwnEvent;

A custom delegate type instead of EventHandler can be used if needed.

如果需要，可以使用自定义委托类型而不是 EventHandler。

You can find detailed information/tutorials on the use of events in .NET in the article Events Tutorial(MSDN).

您可以在文章事件教程(MSDN) 中找到有关在 .NET 中使用事件的详细信息/教程。

回答by Jon Skeet

I have a full discussion of events and delegates in my events article. For the simplest kind of event, you can just declare a public event and the compiler will create both an event and a field to keep track of subscribers:

我在我的事件文章中对事件和代表进行了全面讨论。对于最简单的事件，您只需声明一个公共事件，编译器就会创建一个事件和一个字段来跟踪订阅者：

public event EventHandler Foo;

If you need more complicated subscription/unsubscription logic, you can do that explicitly:

如果您需要更复杂的订阅/取消订阅逻辑，您可以明确地这样做：

public event EventHandler Foo
{
    add
    {
        // Subscription logic here
    }
    remove
    {
        // Unsubscription logic here
    }
}

回答by Basheer AL-MOMANI

to do it we have to know the three components

要做到这一点，我们必须知道三个组成部分

1. the place responsible for firing the Event
2. the place responsible for responding to the Event

3. the Event itself

   a. Event

   b .EventArgs

   c. EventArgs enumeration

1. 负责的地方 firing the Event
2. 负责的地方 responding to the Event

3. 事件本身

   一种。事件

   b .EventArgs

   C。EventArgs 枚举

now lets create Event that fired when a function is called

现在让我们创建在调用函数时触发的事件

but I my order of solving this problem like this: I'm using the class before I create it

但我解决这个问题的顺序是这样的：我在创建它之前使用这个类

1. the place responsible for responding to the Event

   NetLog.OnMessageFired += delegate(object o, MessageEventArgs args) 
   {
           // when the Event Happened I want to Update the UI
           // this is WPF Window (WPF Project)  
           this.Dispatcher.Invoke(() =>
           {
               LabelFileName.Content = args.ItemUri;
               LabelOperation.Content = args.Operation;
               LabelStatus.Content = args.Status;
           });
   };
   

1. 负责的地方 responding to the Event

   NetLog.OnMessageFired += delegate(object o, MessageEventArgs args) 
   {
           // when the Event Happened I want to Update the UI
           // this is WPF Window (WPF Project)  
           this.Dispatcher.Invoke(() =>
           {
               LabelFileName.Content = args.ItemUri;
               LabelOperation.Content = args.Operation;
               LabelStatus.Content = args.Status;
           });
   };
   

NetLog is a static class I will Explain it later

NetLog 是一个静态类我稍后会解释

the next step is

下一步是

1. the place responsible for firing the Event

   //this is the sender object, MessageEventArgs Is a class I want to create it  and Operation and Status are Event enums
   NetLog.FireMessage(this, new MessageEventArgs("File1.txt", Operation.Download, Status.Started));
   downloadFile = service.DownloadFile(item.Uri);
   NetLog.FireMessage(this, new MessageEventArgs("File1.txt", Operation.Download, Status.Finished));
   

2. 负责的地方 firing the Event

   //this is the sender object, MessageEventArgs Is a class I want to create it  and Operation and Status are Event enums
   NetLog.FireMessage(this, new MessageEventArgs("File1.txt", Operation.Download, Status.Started));
   downloadFile = service.DownloadFile(item.Uri);
   NetLog.FireMessage(this, new MessageEventArgs("File1.txt", Operation.Download, Status.Finished));
   

the third step

第三步

1. the Event itself

3. 事件本身

I warped The Event within a class called NetLog

我在一个名为 NetLog 的类中扭曲了事件

public sealed class NetLog
{
    public delegate void MessageEventHandler(object sender, MessageEventArgs args);

    public static event MessageEventHandler OnMessageFired;
    public static void FireMessage(Object obj,MessageEventArgs eventArgs)
    {
        if (OnMessageFired != null)
        {
            OnMessageFired(obj, eventArgs);
        }
    }
}

public class MessageEventArgs : EventArgs
{
    public string ItemUri { get; private set; }
    public Operation Operation { get; private set; }
    public Status Status { get; private set; }

    public MessageEventArgs(string itemUri, Operation operation, Status status)
    {
        ItemUri = itemUri;
        Operation = operation;
        Status = status;
    }
}

public enum Operation
{
    Upload,Download
}

public enum Status
{
    Started,Finished
}

this class now contain the Event, EventArgsand EventArgs Enumsand the functionresponsible for firing the event

这个类现在包含the Event，EventArgs并EventArgs Enums与the function负责触发事件

sorry for this long answer

抱歉这么长的答案