MACROMEDIA FLEX 2-MIGRATING APPLICATIONS TO FLEX 2 Bedienungsanleitung PDF herunterladen (Seite 29)

Initializing variables 29

Doing the latter results in a “Type annotation is not a compile-time constant” error.

Embed

The Embed syntax in ActionScript is [Embed(params)], and this metadata must be used over

a variable. The variable should be of type Class; for example:

[Embed(source="holdon.mp3")]

var sndCls:Class;

public function playSound():void {

var snd:flash.media.Sound = new sndCls();

snd.play();

}

This works in a very similar way to what was implemented in Flex 1.x. The main difference is

that instead of typing the embedded variable String, you type it as Class. In addition,

instantiation relies on the

new operator rather than the attachMovie() and attachSound()

methods.

In Flex 1.x, the

[Embed] metadata was placed before a var, and the var received the linkage ID

that was associated with the asset. In Flex 2, you put the

[Embed] metadata before a class

definition to associate the class with an asset. This change makes the linkage ID unnecessary;

instead, the asset is manifested to the object model as a class.

For backwards compatibility, the variable associated with an

[Embed] can be of type String.

However, this requires you to get the class via the

getDefinitionByName() method. For

example:

[Embed(source="holdon.mp3")]

var sndStr:String;

public function playSound():void {

var sndClass:Class = getDefinitionByName(sndStr);

var snd:flash.media.Sound = new sndCls();

snd.play();

}

Initializing variables

The default values of uninitialized typed variables (and arguments and properties) was always

undefined in ActionScript 2.0, and is almost never undefined in ActionScript 3.0. In

ActionScript 3.0,

undefined is only for use with type Object. Other types can no longer store

the

undefined value. If you assign undefined to other types, it will be coerced into null,

NaN, 0, or false.

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MACROMEDIA FLEX 2-MIGRATING APPLICATIONS TO FLEX 2 Bedienungsanleitung Seite 29