User Guide

Implementing the component 157
Implementing the constructor
Your ActionScript class should define a public constructor method for a class that is a subclass
of the UIComponent class, or a subclass of any child of the UIComponent class. The
constructor has the following characteristics:
■ No return type
■ Should be declared public
■ No arguments
■ Calls the super() method to invoke the superclass’s constructor
Each class can contain only one constructor method; ActionScript does not support
overloaded constructor methods. For more information, see Chapter 3, “Defining the
constructor,” on page 28.
Use the constructor to set the initial values of class properties. For example, you can set
default values for properties and styles, or initialize data structures, such as Arrays.
Do not create child display objects in the constructor; you should use it only for setting initial
properties of the component. If your component creates child components, create them in the
createChildren() method.
Implementing the createChildren() method
A component that creates other components or visual objects within it is called a composite
component. For example, the Flex ComboBox control contains a Te xt In pu t control to define
the text area of the ComboBox, and a Button control to define the ComboBox arrow.
Components implement the
createChildren() method to create child objects (such as
other components) in the component.
You do not call the
createChildren() method directly; Flex calls it when the call to the
addChild() method occurs to add the component to its parent. Notice that the
createChildren() method has no invalidation method, which means that you do not have
to call it a second time after the component is added to its parent.
For example, you might define a new component that consists of a Button control and a
TextArea control, where the Button control enables and disables user input to the TextArea
control. The following example creates the TextArea and Button controls:
// Declare two variables for the component children.
private var text_mc:TextArea;
private var mode_mc:Button;
override protected function createChildren():void {