Tutorialspoint
Problem
Solution
Submissions
Back

Simple Event System Using Delegates

Certification: Intermediate Level Accuracy: 66.67% Submissions: 3 Points: 20

Write a C# program to implement a simple event system using delegates to handle notifications between classes. You'll need to create a publisher class that can notify multiple subscribers when events occur.

Example 1
    

  • Input: Create publisher and two subscribers, subscribe both to events, publish "System update completed"
    • 

  • Output: Both subscribers receive the notification message
    • 

  • Explanation: 
      
   
    • Step 1: Create a publisher with an event and two subscriber objects.
      • 
   
    • Step 2: Subscribe both subscribers to the publisher's event.
      • 
   
    • Step 3: Publisher triggers the event with message "System update completed".
      • 
   
    • Step 4: Each subscriber's notification handler is called with the message.
      • 
   
    • Step 5: Both subscribers print confirmation of receiving the message.
      • 

    •
Example 2
    

  • Input: Create publisher and two subscribers, subscribe both, publish first message, unsubscribe first subscriber, publish second message
    • 

  • Output: Both subscribers receive first message, only second subscriber receives second message
    • 

  • Explanation: 
      
   
    • Step 1: Create a publisher with an event and two subscriber objects.
      • 
   
    • Step 2: Subscribe both subscribers to the publisher's event.
      • 
   
    • Step 3: Publisher triggers first notification, both subscribers receive it.
      • 
   
    • Step 4: First subscriber is unsubscribed from the event.
      • 
   
    • Step 5: Publisher triggers second notification.
      • 
   
    • Step 6: Only second subscriber receives the notification as the first one is no longer subscribed.
      • 

    •
Constraints
    

  • Your solution must use delegates and events (not interfaces)
    • 

  • The system should support adding and removing subscribers dynamically
    • 

  • Time Complexity: O(n) for publishing events, where n is the number of subscribers
    • 

  • Space Complexity: O(n) for storing subscriber references
    •
Functions / MethodsObject-Oriented ProgrammingBitwise OperationsTutorialspointAirbnb
Editorial

Login to view the detailed solution and explanation for this problem.

My Submissions
All Solutions
Refresh
Lang Status Date Code
You do not have any submissions for this problem.
Refresh
User Lang Status Date Code
No submissions found.

Please Login to continue
Solve Problems

 
 
 
Output Window
Clear All Apply Filters

Trending

Others

SIGN IN

Don't have an account? Register

Hint
Solution

Solution Hints

    
  
  • Define a delegate type that matches the signature of the subscriber's notification handler method
    • 
  
  • Use the 'event' keyword in the publisher class to declare the event based on your delegate type
    • 
  
  • Implement methods to add (+=) and remove (-=) handlers from the event
    • 
  
  • Check if the event has subscribers before invoking it to avoid null reference exceptions
    • 
  
  • Consider making the subscriber identifiable (e.g., with a name property) for tracking purposes
    •

Steps to solve by this approach:

 Step 1: Define a delegate type for the notification method
 Step 2: Create an event in the publisher class using the delegate type
 Step 3: Implement methods to subscribe to and unsubscribe from the event
 Step 4: Create a method to trigger the event and notify all subscribers
 Step 5: Create a subscriber class with a handler method that matches the delegate signature

Submitted Code :