Flex 学习之路之十三 用户接口user interface 实现进度条 preloader

preloader:Object - spark.components.Application

应用程序容器支持应用程序预加载器，该预加载器使用下载进度条来显示应用程序 SWF 文件的下载和初始化进度。默认情况下，已启用应用程序预加载器。预加载器跟踪已下载的字节数，并持续更新进度条。

使用此属性指定用于定义自定义进度指示符的组件的路径。要创建自定义进度指示符，通常需要创建 SparkDownloadProgressBar 或 DownloadProgressBar 类的子类，或者创建用于实现 mx.preloaders.IPreloaderDisplay 接口的 flash.display.Sprite 类的子类。

<?xml version="1.0"?><!-- containers\application\SparkMainDPBMin.mxml --><s:Application xmlns:fx="http://ns.adobe.com/mxml/2009"   xmlns:mx="library://ns.adobe.com/flex/mx"   xmlns:s="library://ns.adobe.com/flex/spark"   preloader="myComponents.SparkDownloadProgressBarSubClassMin"><s:layout><s:VerticalLayout/></s:layout><!-- Add a couple of controls that don't do anything. --><s:Button label="Click Me"/><s:TextInput text="This is a TextInput control."/></s:Application>

         

package myComponents{import mx.preloaders.*;import flash.events.ProgressEvent;public class SparkDownloadProgressBarSubClassMin extends SparkDownloadProgressBar{public function SparkDownloadProgressBarSubClassMin() {super();}// Embed the background image.[Embed(source="assets/auto_layout.png")][Bindable]public var imgCls:Class;// Override to set a background image.override public function get backgroundImage():Object{return imgCls;}// Override to set the size of the background image to 100%.override public function get backgroundSize():String{return "100%";}// Override to return true so progress bar appears// during initialization.override protected function showDisplayForInit(elapsedTime:int,count:int):Boolean {return true;}// Override to return true so progress bar appears during download.override protected function showDisplayForDownloading(elapsedTime:int, event:ProgressEvent):Boolean {return true;}}}