Delegate Event Handler: Parameters

In C#, you can define an event handler with a delegate that accepts parameters using the following steps:

1. Define a delegate that matches the signature of the event handler. The delegate specifies the parameters and return type of the event handler method. For example, let’s create a delegate named EventHandlerWithParameter that takes an integer parameter and doesn’t return anything:

delegate void EventHandlerWithParameter(int parameter);

Declare an event of the delegate type in the class where you want to define the event handler. For instance, let’s say we have a class named EventPublisher that declares an event named SomeEvent:

class EventPublisher
{
    public event EventHandlerWithParameter SomeEvent;
    
    // Rest of the class code...
}

Create a method that matches the delegate’s signature. This method will serve as the event handler and will be called when the event is triggered. For example, let’s create a method named HandleEvent that takes an integer parameter:

void HandleEvent(int parameter)
{
    // Event handling logic...
}

Subscribe to the event by adding the event handler method to the event delegate’s invocation list. In this case, you can use the += operator to add the HandleEvent method to the SomeEvent event:

EventPublisher publisher = new EventPublisher();
publisher.SomeEvent += HandleEvent;

Trigger the event when desired. In your code, call the event by using the event publisher object and provide the necessary parameter(s):

int parameterValue = 42;
publisher.SomeEvent?.Invoke(parameterValue);

The event handler method (HandleEvent) will be executed, and it will receive the parameter value passed when invoking the event.

That’s how you can define an event handler with a delegate that accepts parameters in C#.