Macromedia flex 2 Manual

162

Creating Advanced Visual Components in ActionScript

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}

Implementing the measure() method

The 

measure()

 method sets the default component size, in pixels, and optionally sets the 

component’s default minimum size. 

Flex schedules a call to the 

measure()

 method when a call to the 

invalidateSize()

 method 

occurs. The 

measure()

 method executes during the next 

render

 event after a call to the 

invalidateSize()

 method. When you use the 

addChild()

 method to add a component to 

a container, Flex automatically calls the 

invalidateSize()

 method. 

When you set a specific height and width of a component, Flex does not call the 

measure()

 

method, even if you explicitly call the 

invalidateSize()

 method. That is, Flex only calls the 

measure()

 method if the 

explicitWidth

 property or the 

explicitHeight

 property of the 

component is NaN. 

In the following example, because you explicitly set the size of the Button control, Flex does 
not call the 

Button.measure()

 method: 

<mx:Button height="10" width="10"/>

In a subclass of an existing component, you might implement the 

measure()

 method only if 

you are performing an action that requires modification to the default sizing rules defined in 
the superclass. Therefore, to set a new default size, or perform calculations at run time to 
determine component sizing rules, implement the 

measure()

 method. 

You set the following properties in the 

measure()

 method to specify the default size: 

The 

measure()

 method only sets the default size of the component. In the 

updateDisplayList()

 method, the parent container of the component passes to it its actual 

size, which may be different than the default size. 

Properties

Characteristics Description

measuredHeight
measuredWidth

Default height 
and width

Specifies the default height and width of the 
component, in pixels. 
These properties are set to 0 until the measure() 
method executes. Although you can leave them set 
to 0, it makes the component invisible by default. 

measuredMinHeight
measuredMinWidth 

Default minimum 
height and width

Specifies the default minimum height and minimum 
width of the component, in pixels. Flex cannot set 
the size of a component smaller than its specified 
minimum size.