c# What is a delegate and what is an event

The role of delegates and events in C

#Delegates and events are commonly used mechanisms in C# to achieve loose coupling and event processing between codes.

Delegate

• Definition: A delegate is a reference type that points to a method, which allows a method to be passed as a parameter to other methods .
• Function: Delegate transfers the responsibility of calling the method from the caller to the receiver, thereby achieving code reusability and flexibility.

Event

• Definition: An event is a special delegate that represents an action that can be triggered at a specific moment or event.
• Function: Events allow objects to notify external subscribers of the occurrence of specific events, and subscribers can respond to these events.

The relationship between delegation and events

Delegation is the underlying mechanism of events. Events use delegates to manage a list of subscribers and trigger method calls to all subscribers when the event occurs.

Using delegates

To use delegates, you need to follow the following steps:

1. Define a delegate type that is the same as the delegate type you want to call Methods have the same signature.
2. Create an instance of the delegate object that points to the method to be called.
3. Pass the delegate object as a parameter to other methods.

Using events

To use events, you need to follow the following steps:

1. Define an event in a class that Use the delegate type as its type.
2. Subscribers add methods to events through the event = operator.
3. When an event fires, remove the method through the event -= operator or call all subscribers through the event() method.

Example

The following is a simple example using delegates and events:

<code class="csharp">// 定义一个委托
public delegate void MyEventHandler(object sender, EventArgs e);

// 定义一个事件
public event MyEventHandler MyEvent;

// 触发事件
protected virtual void OnMyEvent(EventArgs e)
{
    MyEvent?.Invoke(this, e);
}</code>

<code class="csharp">// 订阅事件
myClass.MyEvent += MyEventHandler;</code>

<code class="csharp">// 触发事件
myClass.OnMyEvent(new EventArgs());</code>

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