Difference between delegates and interfaces in C#

In this article, you will learn about the differences between the delegates and interfaces in C#. But before discussing the differences, you must know about the delegates and interfaces in C# with their syntax and examples.

Introduction of Delegates in C#

In C#, a delegate is a type that represents references to methods with a specific signature. It allows methods to be treated as entities that can be assigned to variables, passed as parameters to other methods, and called dynamically. Delegates provide a way to achieve a callback function where you can pass a method as an argument to another method and have that method call the accepted method.

Here is a basic introduction to C# delegates:

It declares a delegate named Delegate, which can refer to methods that take an integer parameter and return a null value. You can customize the delegate signature depending on the method you want to reference.

Establish a representative:

This is the "SomeMethod" method that matches the Delegate signature. Now, the Commissioner refers to this method.

Call a Delegate:

It calls the method referenced by the delegate and passes an integer value of 10.

Multicasting with delegates:

Delegates can refer to multiple methods, enabling multicasting:

Now, when you call myDelegate, it will call both "SomeMethod", "AnotherMethod", and "YetAnotherMethod" in the order they were added.

Use Cases of Delegates:

There are several use cases of the delegates in C#. Some main use cases of the delegates are as follows:

1. Callback Mechanism:

Delegates are often used to implement callback mechanisms where a method delegates part of an operation to a method provided by the caller.

2. Event handling:

Delegates are widely used in C# event handling. Events are based on delegates and are a way to notify when certain actions have occurred.

3. Asynchronous programming:

Delegates are used in asynchronous programming to invoke methods asynchronously, especially the BeginInvoke and EndInvoke methods.

4. LINQ:

Delegates are used in LINQ queries for predicate functions or to define a key selector in sort operations. Delegates play an important role in achieving flexibility and decoupling in C# code by allowing methods to be treated as first-class citizens. They are an integral part of the language and support functional programming concepts.

Program for Delegates:

Let us take an example to illustrate the delegates in C#.

Output:

When you run this program, you should see the following output:

PrintNumber: 42
PrintNumber: 10
DoubleNumber: 20

Explanation:

In this example, MyDelegate is declared as a delegate that can refer to methods that take an integer parameter and return null. The methods "PrintNumber" and "DoubleNumber" correspond to the delegated signature. An instance of "Delegate" is created and assigned the "PrintNumber" method.

A delegate is called with an integer "argument". Another method (DoubleNumber) is added to the delegate using the += syntax. The delegate is called again, and this time both methods (PrintNumber and DoubleNumber) are called.

Introduction of interfaces in C#

Interface declaration: A C# interface is a reference type that defines the implementation contract of classes. It acts as a blueprint that defines a set of method signatures, property signatures, events, and indexers without providing an implementation.

Syntax:

It has the following syntax:

Key Features:

There are several key features of the interfaces in C#. Some main key features of the interfaces are as follows:

Abstraction: Interfaces provide a level of abstraction by defining a common convention that implementing classes must follow.

Method signatures: Interfaces contain method signatures without specifying how those methods should be implemented.

Properties, events, and indexers: In addition to methods, interfaces can also declare properties, events, and indexers that implementing classes must define.

Implementing multiple interfaces: A C# class can implement multiple interfaces, allowing it to follow multiple conventions simultaneously.

class MyDerivedClass: IExampleInterface, IAnotherInterface.

Use cases:

There are several use cases of interface. Some main use cases of interface are as follows:

Polymorphism: Interfaces allow polymorphism by allowing objects of different classes to be handled uniformly by an interface type.

Dependency Injection: Interfaces are often used in dependency injection scenarios, promoting loose coupling and flexibility in the code architecture.

API design: Interfaces are valuable in API design because they provide a clear contract for users of a particular library or module.

Program for interfaces in C#

Let us take an example to illustrate the interface in C#.

Output:

When you run this program, you should see the following output:

Circle Area: 78.54
Rectangle Area: 24.00

Explanation:

In this program, we define the "IShape" interface with one "CalculateArea" method.

Two classes, Circle and Rectangle, implement the "IShape" interface, providing implementations of its "CalculateArea" method. In the Main method, we create instances of both classes and treat them as "IShape" objects. After that, we call the "CalculateArea" method for each shape, and the appropriate implementation is called based on the actual type of the object.

Difference between delegates and interfaces in C#

Delegates and interfaces are both important concepts in C# that facilitate various aspects of programming. Here are the main differences between delegates and interfaces:

Purpose:

Delegates: Delegates are used to create references to methods and call those methods via a delegate object. They are mostly used to implement callback mechanisms, event handling and the observation design pattern.

Interfaces: Interfaces define the contract implemented in classes. They are used to declare a set of methods, properties, events, or indexers that a class must provide. Interfaces are used to achieve abstraction and implement a common structure between classes.

Contract type:

Delegates: Delegates allow you to create references to methods with a specific signature. They focus more on method signatures and function pointers.

Interfaces: Interfaces define a convention that a class must follow. It contains the set of method signatures, properties, events, or indexers that the implementation class must provide.

Number of methods:

Delegates: A delegate can represent a single method or a chain of methods (multicast delegate) with the same signature.

Interfaces: Interfaces can declare multiple methods, properties, events, or indexes that must be provided by the class implementing the interface.

Implementation:

Delegates: Delegates are implemented by the delegate keyword and are instantiated by a method or set of methods that match the delegate signature.

Interfaces: Interfaces are implemented using the interface keyword. A class can implement one or more interfaces, providing specific implementations for each member of the interface.

Flexibility:

Delegates: Delegates provide more flexibility in dynamically defining methods at runtime and creating event-handling mechanisms.

Interfaces: Interfaces provide a more structured approach and are often used when a group of classes must follow a common set of methods.

Event Handling:

Delegates: Delegates are commonly used to handle events in C#, allowing multiple methods to subscribe to an event.

Interfaces: Although interfaces themselves are not directly used to process transactions, they can be associated with transactions to define a contract for subscribers to the transaction.

Inheritance:

Delegates: Delegates do not support inheritance. Each delegate type is self-contained and cannot be derived or inherited from other delegate types.

Interfaces: Interfaces support inheritance. A class can implement multiple interfaces, and the interfaces themselves can inherit from other interfaces, allowing for a hierarchical structure.

Null ability:

Delegates: Delegates can be nullable, meaning they don't necessarily have to refer to a method. This attribute is often used to check if a delegate has subscribed methods before calling them.

Interfaces: Interface instances cannot be empty because they are implemented by a class. However, reference variables of an interface type can be null if they are not assigned to an instance of a class that implements that interface.

Compile Time Vs. runtime binding:

Delegates: Delegates provide dynamic or runtime binding. The actual method to be called is determined at runtime when the delegate is called.

Interfaces: Interface methods are bound at compile time. The compiler ensures that a class implementing an interface provides concrete implementations for all members of the interface.

Multiple method signatures:

Delegates: A single delegate type can represent methods with different signatures as long as they match the delegate's return type and parameter types.

Interfaces: Each method on an interface must have a unique signature on that interface, which encourages strict definitions of method contracts.

Performance:

Delegates: Delegates can be a bit of a burden in having to create and call delegate objects, especially for multi-role delegates.

Interfaces: Interface method calls can have better performance because they are resolved at compile time and do not incur the overhead associated with delegates.

Anonymous Methods and Lambdas:

Delegates: Delegates can be easily used with anonymous methods and lambda expressions, providing concise ways to define method implementations inline.

Interfaces: Although interfaces themselves do not support anonymous methods or lambdas, a class implementing an interface can use these features to implement interface members.

Conclusion:

Delegates and interfaces are fundamental C# concepts that play a special role in shaping the design and functionality of object-oriented applications. Understanding the key differences between these two structures is important for developers who want to use their skills effectively.

Delegates, which function primarily as function pointers, provide a mechanism for creating references to methods. Their primary purpose is to enable dynamic invocation of methods, which allows the implementation of callback mechanisms and supporting scenarios such as event handling. Delegates declared with the delegate keyword allow methods to be encapsulated and passed as parameters, stored in data structures, or called dynamically at runtime. This flexibility makes delegates useful in scenarios where the exact execution method is known only at runtime. They significantly advance the event-oriented programming paradigm by allowing multiple methods to be attached to a given event and invoked via multicast delegates.

On the other hand, interfaces focus on defining a convention that classes must follow by defining a set of method signatures, properties, events, or indexers. The interface keyword is used to declare interfaces, and implementation classes are needed to provide specific implementations for all members defined in the interface. Interfaces play a crucial role in achieving multiple inheritance in C# by allowing a class to implement multiple interfaces. It promotes code reusability and ensures a consistent structure between classes, making interfaces a key element of the object-oriented programming paradigm.

One of the most important differences between delegates and interfaces is their implementation of inheritance. Delegates do not support multiple inheritance, limiting class inheritance from a single delegate. On the other hand, interfaces are great for providing multiple inheritance solutions by allowing a class to implement multiple interfaces. This distinction highlights the role of interfaces in creating a more modular and extensible codebase because classes can inherit behavior from multiple sources without the constraints of a single inheritance.

Event handling is an area where delegates excel, as they are typically used to implement this important part of C# programming. Events in C# are essentially multicast delegates that allow multiple methods to be attached to an event. In this context, delegates work as a means of encapsulating methods that respond to the occurrence of an event, providing a clean and efficient way to implement the observer model. Although interfaces do not directly handle events, they are often used in conjunction with patterns, such as the EventSubscriber pattern, to define contracts for classes that intend to subscribe to events.

For flexibility and usability, delegates are especially valuable in scenarios that require dynamic method invocation, such as asynchronous programming or situations where the called method may change at runtime. Their ability to dynamically encapsulate and invoke methods makes them suitable for scenarios where the exact method is not known at compile time. On the other hand, interfaces provide a more structured and statically defined approach to achieving shared functionality between classes. They promote code consistency, reusability, and maintainability by enforcing a standardized convention that implementers of classes must follow.

In conclusion, while both delegates and interfaces make significant contributions to the C# programming environment, their roles and applications differ significantly. Delegates are great in scenarios that require dynamic method invocation and event handling, providing a flexible mechanism for method reference and execution. On the other hand, interfaces focus on defining class contracts, promoting code reusability, and facilitating multiple inheritance. The choice between delegates and interfaces depends on the specific requirements of the application, and careful consideration of their strengths and limitations is essential to effective software design in C#.