@ Can the robot explain in detail the commissions and events of C#in thousands of words?

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• • Wolf at the end of the desert **:@Can the robot explain in detail the commissions and events of C#in thousands of words?
• • Robot **:@The wolf at the end of the desert can of course. The following is a detailed explanation of the commissions and events in C#.

Delegate and event are two important concepts in C#, and they are the key to realizing event-driven programming. Delegates and events are often used to implement callback mechanisms and are at the core of many important APIs in the. NET framework, such as Windows Forms and ASP.NET.

1. Entrusted

Delegate is a type that references a method, which can pass a method as an argument to other methods, or between methods. A delegate is essentially a class with a signature and a method table that can associate multiple methods with the same delegate object.

The syntax for defining delegates is as follows:

delegate returnType delegateName(parameterList);

Where, returnType is the return value type, delegateName is the delegate name, and parameterList is the parameter list. For example, you can define a delegate with the following code:

delegate void MyDelegate(string message);

This delegate takes a string parameter and returns type void.

Delegates allow you to pass methods as parameters to other methods, such as:

void Method1(string message) {
    Console.WriteLine(message);
}

void Method2(MyDelegate del, string message) {
    del(message);
}

MyDelegate del = new MyDelegate(Method1);
Method2(del, "Hello, world!");

In this example, Method 1 is a method that accepts a string parameter and prints it to the console, and Method 2 is a method that accepts a delegate of type MyDelegate and a string parameter, passing the delegate along with the string parameter to the del method. The del method accepts a string parameter and passes it to the method associated with the delegate, Method 1.

In addition to using delegates to pass methods as parameters to other methods, you can also use delegates to group multiple methods together. For example, you can use a delegate to connect two methods so that they execute in turn when the delegate is called. This way of combining multiple methods is called "multicast delegation."

The syntax for defining multicast delegation is as follows:

delegateName += methodName;
delegateName -= methodName;

Where delegateName is the name of the multicast delegate, and methodName is the name of the method to connect or disconnect. For example:

MyDelegate del1 = new MyDelegate(Method1);
MyDelegate del2 = new MyDelegate(Method2);
MyDelegate del3 = del1 + del2;
del3("Hello, world!");

In this example, two delegates are first defined, the MyDelegate types associated with Method 1 and Method 2. Then, the two delegates are combined into a multicast delegate del3, and Method 1 and Method 2 are executed in turn when del3 is called.

2. Events

An event is a special delegate that can only be activated by a trigger and not by other classes

• • Wolf at the end of the desert **:@Robot, please continue
• • Robot **:@Call from the wolf at the end of the desert. In C#, events are often used to implement a mechanism for passing messages between classes. The use of events separates publishers and subscribers of events, resulting in a more loosely coupled code design.

The syntax for defining events is as follows:

public event delegateName eventName;

where public is the access modifier, delegateName is the name of the delegate, and eventName is the name of the event. For example:

public delegate void MyDelegate(string message);

public class MyClass {
    public event MyDelegate MyEvent;
    
    public void RaiseEvent(string message) {
        MyEvent(message);
    }
}

public class Program {
    static void Main() {
        MyClass obj = new MyClass();
        obj.MyEvent += new MyDelegate(Method1);
        obj.MyEvent += new MyDelegate(Method2);
        obj.RaiseEvent("Hello, world!");
    }
    
    static void Method1(string message) {
        Console.WriteLine("Method1: " + message);
    }
    
    static void Method2(string message) {
        Console.WriteLine("Method2: " + message);
    }
}

In this example, a class called MyClass is defined that contains an event called MyEvent, and its delegate type is MyDelegate. The MyClass class also contains a method called RaiseEvent, which triggers the MyEvent event and passes the message to all delegates associated with the event.

In the program's Main method, a MyClass object is first created, and then the "+=" operator is used to associate two delegates with the MyEvent event. Finally, call the RaiseEvent method to trigger the MyEvent event, setting "Hello, world!" The message is passed to two delegates. Because these two delegates are associated with the Method 1 and Method 2 methods, respectively, they will print messages in the console.

It should be noted that events can only be triggered inside the class that contains the event, and external classes cannot directly trigger events. This protects event subscribers from accidental modifications or resets by other types.

summary

Delegates and events are important concepts in C#that provide the core mechanism for event-driven programming. Delegate is a type that references a method, which can pass a method as an argument to other methods, or between methods. An event is a special delegate that can only be activated by triggers and cannot be called by other classes. When using events, you can separate the publisher and subscriber of the event, resulting in a more loosely coupled code design.

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