如何在 C# 中创建自己的事件？

Question

如何在 C# 中创建自己的事件？

Answer 1

要做到这一点，我们必须知道三个组件

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

3. 事件本身

   一个。事件

   b .EventArgs

   c。 EventArgs 枚举

现在让我们创建在调用函数时触发的事件

但我解决这个问题的顺序是这样的：我在创建类之前使用它

1. 负责responding to the Event的地方

   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是一个静态类，后面会解释

下一步是

1. 负责firing the Event的地方

   //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));
   

第三步

1. 事件本身

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
}

这个类现在包含负责触发事件的the Event、EventArgs和EventArgs Enums和the function

抱歉这么长的回答

Answer 2

这是一个使用 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();
        }
    }
}

Answer 3

您可以使用以下代码声明事件：

public event EventHandler MyOwnEvent;

如果需要，可以使用自定义委托类型而不是 EventHandler。

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

Answer 4

我的events article 对活动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;

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
    }
}