C# Events

In C#, an event is a way for objects to communicate with each other and respond to actions or changes in state. Events provide a mechanism for one object (the publisher) to notify other objects (subscribers) that something has happened. In this tutorial, we'll discuss how to define and use events in C#.

Syntax

The syntax for defining an event in C# is as follows:

public event EventHandler MyEvent;

The event keyword is used to define an event in C#. The delegate is used to define the method of the event handlers.

Example

Let's say we want to create a class called "Counter" that raises an event whenever its value changes. Here's how we can implement it:

public class Counter {

   private int _value;
   public event EventHandler ValueChanged;

   public int Value {
      get {
         return _value;
      }
      set {
         if (_value != value) {
            _value = value;
            OnValueChanged();
         }
      }
   }

   protected virtual void OnValueChanged() {
      ValueChanged?.Invoke(this, EventArgs.Empty);
   }
}

Now, we can use the Counter class and subscribe to the ValueChanged event:

Counter c = new Counter();
c.ValueChanged += OnValueChanged;
c.Value = 10;

private void OnValueChanged(object sender, EventArgs e) {
   Console.WriteLine("Value changed to: " + ((Counter)sender).Value);
}

Output

When we run the example code above, the output will be:

Value changed to: 10

This is because we subscribed to the ValueChanged event and printed the new value of the counter to the console.

Explanation

In the example above, we created a class called "Counter" that has a private variable called _value, and an event called ValueChanged. The Value property of the Counter class checks if the new value is different from the previous value, and raises the ValueChanged event if it is.

We then created an instance of the Counter class and subscribed to the ValueChanged event. Whenever the Value of the counter changes, the OnValueChanged method is called, which invokes the ValueChanged event and raises it to all subscribers.

Finally, we created an event handler method called "OnValueChanged" that prints the new value of the counter to the console.

Use

Events are useful for creating communication between objects, and for enabling loose coupling between objects in a system. You can use events to define a contract for how your objects communicate with each other, and to allow for decoupled components to react to changes in other parts of the system.

Important Points

• Events are a way for objects to communicate with each other and respond to actions or changes in state.
• Events provide a mechanism for one object (the publisher) to notify other objects (subscribers) that something has happened.
• The event keyword is used to define an event in C#.
• The EventHandler delegate is used to define the method signature of the event handlers.

Summary

In this tutorial, we discussed how to define and use events in C#. We covered the syntax, example, output, explanation, use, and important points of events in C#. With this knowledge, you can now use events in your C# code to create communication between objects and enable loose coupling between components in your system.