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Understanding Methods

In addition to properties, most objects have methods. Methods are actions the object can perform, in contrast to attributes that describe the object. To understand this distinction, think about the Pet object example. A Dog object has a certain set of actions that it can perform. These actions, called methods in Visual Basic, include barking and tail wagging. Figure 3.6 illustrates the Dog object and its methods.

Figure 3.6. Invoking a method causes the object to perform an action.

Triggering Methods

Think of methods as functions—which is exactly what they are. When you invoke a method, code is executed. You can pass data to the method, and methods might return values. However, a method is neither required to accept parameters (data passed by the calling code) nor to return a value; many methods simply perform an action in code. Invoking (triggering) a method is similar to referencing the value of a property; you first reference the object's name, then a "dot," and then the method name as shown next:


For example, to make the hypothetical Dog object Bruno bark using Visual Basic code, you would use this line of code:


Invoking methods is simple; the real skill lies in knowing what methods an object supports and when to use a particular method.

Understanding Method Dynamism

Properties and methods go hand in hand, and at times a particular method might become unavailable because of one or more property values. For example, if you were to set the NumberofLegs on the Dog object Bruno equal to zero, the Walk and Fetch methods would obviously be inapplicable. If you were to set the NumberofLegs property back to four, you could then trigger the Walk or Fetch methods again.

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