Specifications

CHAPTER 4

The weakRef parameter to the addEventListener() method provides you with some control over memory

resources for listeners. A strong reference (when

weakRef is false) prevents the listener from being garbage

collected. A weak reference (when

weakRef is true) does not. The default is false.

For more information about the

removeEventListener() method, see “Using Events” on page 61 in the Adobe

Flex 3 Developer Guide.

Using styles

You use styles to define the look and feel of your Flex applications. You can use them to change the appearance of

a single component, or apply them globally. Be aware that some methods of applying styles are more expensive

than others. You can increase your application’s performance by changing the way you apply styles.

For more information about using styles, see “Using Styles and Themes” on page 589 in the Adobe Flex 3

Developer Guide.

Loading stylesheets at run time

You can load stylesheets at run time by using the StyleManager. These style sheets take the form of SWF files that

are dynamically loaded while your Flex application runs.

By loading style sheets at run time, you can load images (for graphical skins), fonts, type and class selectors, and

programmatic skins into your Flex application without embedding them at compile time. This lets skins and fonts

be partitioned into separate SWF files, away from the main application. As a result, the application’s SWF file size

is smaller, which reduces the initial download time. However, the first time a run-time style sheet is used, it takes

longer for the styles and skins to be applied because Flex must download the necessary CSS-based SWF file.

For more information, see the Adobe Flex 3 Developer Guide.

Reducing calls to the setStyle() method

Run-time cascading styles are very powerful, but use them sparingly and in the correct context. Calling the

setStyle() method can be an expensive operation because the call requires notifying all the children of the

newly-styled object. The resulting tree of children that must be notified can be quite large.

A common mistake that impacts performance is overusing or unnecessarily using the

setStyle() method. In

general, you only use the

setStyle() method when you change styles on existing objects. Do not use it when you

set up styles for an object for the first time. Instead, set styles in an

<mx:Style> block, as style properties on the

MXML tag, through an external CSS style sheet, or as global styles.