IT1811 Delegates and Events

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Questions and Answers

What is the correct syntax to declare a delegate that returns an integer and takes two integer parameters?

public delegate int mathOp(int x; int y);

delegate void mathOp(int x, int y);

delegate int mathOp(int x int y);

public delegate int mathOp(int x, int y); (correct)

Which keyword is used to instantiate a delegate?

add

new (correct)

instantiate

create

In the declaration of a delegate, what must match with the signature of the referenced method?

The access modifier

The number of parameters

The return type

Both B and C (correct)

What is the purpose of the delegate keyword in .NET?

To allow encapsulation of a method Signup and view all the answers

When invoking a referenced method using a delegate, which of the following is NOT a requirement?

The method must be static. Signup and view all the answers

What does the expression 'GetAnswer mdAdd = new GetAnswer(Formula.getSum);' represent?

The instantiation of a delegate Signup and view all the answers

In a delegate declaration, what is the significance of including an access modifier?

It specifies where the delegate can be accessed. Signup and view all the answers

What happens if the signature of the delegate does not match the referenced method?

Compilation will fail with an error. Signup and view all the answers

What is the correct way to call a delegate after it has been initialized?

MessageBox.Show(delegateAddition(10,20)) Signup and view all the answers

What defines a generic delegate's parameter and return type?

The data types specified within its declaration Signup and view all the answers

Which statement is true about generic delegates?

They are not bound to any specific type. Signup and view all the answers

In what way do delegates and interfaces differ?

Delegates include method calls, while interfaces only declare methods. Signup and view all the answers

What is a consequence of using generic delegates in programming?

They allow functions to accept variables of multiple types without casting. Signup and view all the answers

What would happen if 'X' in the generic delegate declaration is substituted for 'string'?

The delegate can point to methods that have a single string parameter. Signup and view all the answers

How does the syntax for declaring a generic delegate look?

public delegate X MethodName(X arg); Signup and view all the answers

Which statement correctly describes the calling of an interface?

Interfaces cannot be called directly without an instance. Signup and view all the answers

What is the primary purpose of delegates in C#.NET?

To provide safe callbacks without implementations. Signup and view all the answers

Which of the following is true about interfaces?

A class must implement all methods from an interface. Signup and view all the answers

How are methods registered to an event in C#.NET?

Using delegates that specify the method's signature. Signup and view all the answers

What occurs when an event is fired in C#.NET?

Any registered methods are automatically executed. Signup and view all the answers

What must be done before declaring an event in C#.NET?

Declare a delegate associated with the event. Signup and view all the answers

In terms of performance, which of the following is true regarding delegates?

They are slower to get but faster to execute. Signup and view all the answers

Which of the following statements is a characteristic of interfaces in C#.NET?

They allow extending functionality of some objects. Signup and view all the answers

What feature distinguishes delegates from interfaces?

Delegates are primarily for event handling and callbacks. Signup and view all the answers

What is the purpose of the += operator when working with events?

To add a delegate to an event Signup and view all the answers

Which components are generated automatically by the compiler when using the += operator for events?

Add and Remove accessors Signup and view all the answers

What is a characteristic of the event accessors add and remove?

They can contain additional code for condition checks Signup and view all the answers

What must be included when declaring an event in C#?

The access modifier, event keyword, delegate name, and event name Signup and view all the answers

Which class is referenced in the content as containing the method that computes the sum of two numbers?

EventAccessorClass Signup and view all the answers

What does the event accessor 'remove' do?

Unregisters a subscriber from an event Signup and view all the answers

What is the basic structure of declaring an event in C#?

public event delegate_name event_name Signup and view all the answers

In the context of events, what is typically added within the add and remove accessors?

Conditional checks for subscription Signup and view all the answers

Study Notes

Delegates Overview

A delegate is a reference type in .NET that encapsulates a method, allowing methods to be passed as parameters.
To declare a delegate, use the delegate keyword followed by the return type, delegate name, and parameters.
Example of declaration: public delegate int mathOp(int x, int y);
Instantiation involves using the new keyword to associate the delegate with a method, e.g., GetAnswer mdAdd = new GetAnswer(Formula.getSum);.

Invoking Delegates

Delegates enable invoking referenced methods.
When referencing methods returning values, delegate signatures must match the method signatures in terms of parameter count and type.
Delegate invocation uses parentheses to pass arguments, e.g., MessageBox.Show(delegateAddition(10,20).ToString());.

Generic Delegate Types

Generic delegates can reference methods with varying parameter and return types.
A generic delegate example is public delegate X DisplayOutput(X arg);, which allows for parameters and return types defined by X.
If X is replaced with double, the delegate can reference any method returning a double with a double parameter.

Differences Between Delegates and Interfaces

Delegates provide safe callbacks without implementation, while interfaces require implementation of methods.
Delegates can reference any class method with matching signatures and return types.
Interfaces allow multiple implementations and are slower to execute compared to delegates which are faster but require more setup.

Event Handling in C#

Events in C# are triggered by user actions, such as mouse clicks or key presses.
An event is a class member that invokes registered methods upon occurrence, using delegates to define method signatures.
Event handlers are the methods executed when an event occurs.

Event Declaration

Declare a delegate associated with the event before the event can be created.
Syntax for declaring an event: public event delegate_name event_name;, where delegate_name is the previously declared delegate type.
To register a delegate to an event, use the += operator, e.g., event_name += delegate_instance;.

Event Accessors

Adding a delegate to an event creates two automatic accessors: add and remove.
The add accessor registers to the event, while the remove un-registers.
Event accessors can include custom logic for conditions before registering or unregistering.

Example: Event Accessor Usage

The CalculateSum delegate can reference methods that accept parameters and return values.
An example class, EventAccessorClass, may include methods to compute the sum based on user input.

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Description

This quiz covers the concepts of delegates in .NET, focusing on their definition, usage, and the process of declaring and instantiating a delegate. Understand how delegates encapsulate methods and the importance of method signatures. Test your knowledge on this essential programming component!