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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?
Which keyword is used to instantiate a delegate?
In the declaration of a delegate, what must match with the signature of the referenced method?
What is the purpose of the delegate keyword in .NET?
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When invoking a referenced method using a delegate, which of the following is NOT a requirement?
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What does the expression 'GetAnswer mdAdd = new GetAnswer(Formula.getSum);' represent?
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In a delegate declaration, what is the significance of including an access modifier?
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What happens if the signature of the delegate does not match the referenced method?
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What is the correct way to call a delegate after it has been initialized?
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What defines a generic delegate's parameter and return type?
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Which statement is true about generic delegates?
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In what way do delegates and interfaces differ?
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What is a consequence of using generic delegates in programming?
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What would happen if 'X' in the generic delegate declaration is substituted for 'string'?
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How does the syntax for declaring a generic delegate look?
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Which statement correctly describes the calling of an interface?
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What is the primary purpose of delegates in C#.NET?
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Which of the following is true about interfaces?
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How are methods registered to an event in C#.NET?
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What occurs when an event is fired in C#.NET?
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What must be done before declaring an event in C#.NET?
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In terms of performance, which of the following is true regarding delegates?
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Which of the following statements is a characteristic of interfaces in C#.NET?
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What feature distinguishes delegates from interfaces?
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What is the purpose of the += operator when working with events?
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Which components are generated automatically by the compiler when using the += operator for events?
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What is a characteristic of the event accessors add and remove?
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What must be included when declaring an event in C#?
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Which class is referenced in the content as containing the method that computes the sum of two numbers?
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What does the event accessor 'remove' do?
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What is the basic structure of declaring an event in C#?
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In the context of events, what is typically added within the add and remove accessors?
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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 byX
. - If
X
is replaced withdouble
, 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
andremove
. - The
add
accessor registers to the event, while theremove
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!