IT1811 Delegates and Events
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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?

    <p>To allow encapsulation of a method</p> Signup and view all the answers

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

    <p>The method must be static.</p> Signup and view all the answers

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

    <p>The instantiation of a delegate</p> Signup and view all the answers

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

    <p>It specifies where the delegate can be accessed.</p> Signup and view all the answers

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

    <p>Compilation will fail with an error.</p> Signup and view all the answers

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

    <p>MessageBox.Show(delegateAddition(10,20))</p> Signup and view all the answers

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

    <p>The data types specified within its declaration</p> Signup and view all the answers

    Which statement is true about generic delegates?

    <p>They are not bound to any specific type.</p> Signup and view all the answers

    In what way do delegates and interfaces differ?

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

    What is a consequence of using generic delegates in programming?

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

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

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

    How does the syntax for declaring a generic delegate look?

    <p>public delegate X MethodName(X arg);</p> Signup and view all the answers

    Which statement correctly describes the calling of an interface?

    <p>Interfaces cannot be called directly without an instance.</p> Signup and view all the answers

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

    <p>To provide safe callbacks without implementations.</p> Signup and view all the answers

    Which of the following is true about interfaces?

    <p>A class must implement all methods from an interface.</p> Signup and view all the answers

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

    <p>Using delegates that specify the method's signature.</p> Signup and view all the answers

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

    <p>Any registered methods are automatically executed.</p> Signup and view all the answers

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

    <p>Declare a delegate associated with the event.</p> Signup and view all the answers

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

    <p>They are slower to get but faster to execute.</p> Signup and view all the answers

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

    <p>They allow extending functionality of some objects.</p> Signup and view all the answers

    What feature distinguishes delegates from interfaces?

    <p>Delegates are primarily for event handling and callbacks.</p> Signup and view all the answers

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

    <p>To add a delegate to an event</p> Signup and view all the answers

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

    <p>Add and Remove accessors</p> Signup and view all the answers

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

    <p>They can contain additional code for condition checks</p> Signup and view all the answers

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

    <p>The access modifier, event keyword, delegate name, and event name</p> Signup and view all the answers

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

    <p>EventAccessorClass</p> Signup and view all the answers

    What does the event accessor 'remove' do?

    <p>Unregisters a subscriber from an event</p> Signup and view all the answers

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

    <p>public event delegate_name event_name</p> Signup and view all the answers

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

    <p>Conditional checks for subscription</p> 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!

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