IT1811: Delegates and Events

Delegates

• A delegate is a class in .NET that encapsulates a method, acting as a reference type data type for method referencing.
• Only methods that match the delegate's signature can be called.
• Syntax for declaring a delegate includes the delegate keyword, an access modifier, a return type, a delegate name, and parameters in parentheses.
• Example declarations:
  • public delegate int mathOp(int x, int y);
  • public delegate void errorMessage();

Instantiating Delegates

• Use the new keyword to create an instance of the delegate that points to a specific method.
• Example of instantiation:
  • GetAnswer mdAdd = new GetAnswer(Formula.getSum);
  • GetAnswer mdAdd = Formula.Addition;

Invoking Delegates

• Delegates can invoke referenced methods, requiring matching parameters if referencing a method with a return type.
• In classes, after setting up delegate methods and initializing, call the delegate using parentheses to execute.
• Example of invoking a method:
  • MessageBox.Show(delegateAddition(10,20).ToString());

Generic Delegate Types

• Generic delegates are flexible and not restricted to specific data types, capable of referencing methods with varying parameter and return types.
• Example declaration of a generic delegate:
  • public delegate X DisplayOutput(X arg);
• The delegate can point to methods returning type X with a single parameter of type X.

Differences Between Delegates and Interfaces

• Delegates serve as safe callback methods without implementation, while interfaces define contracts for classes with specific method signatures.
• Both can declare methods, but they differ in usage and execution style, such as handling callbacks versus providing a method framework.