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;
		}
	}
}