Standard delegate and Event _ 1, framework_1 in. Net Framework

Standard delegate and Event _ 1, framework_1 in. Net Framework

The standard delegate in. Net Framework has been defined in the namespace System,

namespace System{    public delegate void EventHandler(object sender, EventArgs e);}

All events in the. Net Framwork class library are based on the EventHandler delegate.

The EventArgs parameter is customizable and must inherit the EventArgs class:

public class CustomEventArgs:EventArgs

There are three ways to publish events:

1. Use. net framework standard Delegation

public event EventHandler RaiseCustomEvent;

2. Custom EventArgs Parameters

public event CustomEventHandler RaiseCustomEvent;

3. Custom EventArgs parameter, generic expression

public event EventHandler<CustomEventArgs> RaiseCustomEvent;

 

How to: publish events that comply with the. net framework guidelines

There are two classes:

1. The Publisher class (Publisher) is the class that Sends (triggering Raise) events. This class does two things.

• Release events
• Compile the event trigger Program

Events (such as Load and Click) are released in the Form and control classes. The event trigger program can also be found as follows:

protected virtual void OnClick(EventArgs e);

 

2. Subscriber class, which receives the Receive (processing Handle) event class. This class does two things.

• Register an event
• Compile an event handler

When you double-click a button in Form1

        private void button1_Click(object sender, EventArgs e)        {        }

It is actually writing the event processing program. In Form1.Designer. cs, the event will be automatically registered and double-clicked.

this.button1.Click += new System.EventHandler(this.button1_Click);

 

The following example shows how to add custom events in a standard way:

namespace DotNetEvents{    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();            Console.WriteLine("Press Enter to close this window.");            Console.ReadKey();        }    }    //Define a class to hold custom event info    public class CustomEventArgs:EventArgs    {        private string message;        public CustomEventArgs (string s)        {            message = s;        }        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 oveeride 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 raise            if(RaiseCustomEvent !=null )            {                e.Message = String.Format(" at {0}", DateTime.Now.ToString());                RaiseCustomEvent(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 suing C# 2.0 syntax            pub.RaiseCustomEvent += HandleCustomEvent;        }        //Define what action to take when the event is raised        void HandleCustomEvent(object sender,CustomEventArgs e)        {            Console.WriteLine(id + " receive this message: {0}", e.Message);        }    }}