Learning C# 3.0

Chapter 17: Delegates and Events

Quiz Solutions

Solution to Question 17-1. The purpose of a delegate is to decouple the method(s) called from the calling code. It allows the designer of an object to define the delegate, and the user of the object to define which method will be called when the delegate is invoked.

Solution to Question 17-2. Delegates are reference types, but instead of referring to an object, they refer to a method.

Solution to Question 17-3. You instantiate a previously defined delegate named OnPhoneRings like this:

OnPhoneRings myDelegate = new OnPhoneRings(myMethod);

Solution to Question 17-4. The following is the standard way to define a delegate for an event handler:

public delegate void PhoneRangHandler
( object sender, EventArgs e );

You then use the event keyword to restrict the delegate such that it can be invoked only by the defining class:

public event PhoneRangHandler PhoneHasRung;

Solution to Question 17-5. Here is how to call a delegated method:

PhoneHasRung(this, new EventArgs( ));

Solution to Question 17-6. The event keyword limits the use of the delegate in the following ways:

• You can only add a method using +=.

• You can only remove a method using -=.

• The delegate can be invoked only by the class that defines it.

Solution to Question 17-7. To pass information to the method called through the event, define the delegate to take as its second parameter an object of a type derived from EventArgs. Pass the information through properties of that object.

Solution to Question ...