backgroundtask.java

j2me测试实现httpconn和自己实现list等功能

/*
 * Created on 2005-2-26
 *
 * TODO To change the template for this generated file go to
 * Window - Preferences - Java - Code Style - Code Templates
 */
package com.favo.ui;

import javax.microedition.lcdui.AlertType;
import javax.microedition.lcdui.Displayable;
import javax.microedition.lcdui.Display;
import javax.microedition.lcdui.Alert;


/**
 * @author liyong
 * 
 * TODO To change the template for this generated type comment go to Window -
 * Preferences - Java - Code Style - Code Templates
 */
public abstract class BackgroundTask extends Thread implements Cancelable {

	ProgressObserver poUI;

	protected Displayable preScreen;

	protected boolean needAlert;

	protected Alert alertScreen;

	private Display display;

	/*
	 *  
	 */
	public BackgroundTask(ProgressObserver poUI, Displayable pre,
			Display display) {
		this.poUI = poUI;
		this.preScreen = pre;
		this.display = display;
		this.needAlert = false;
	}

	/*
	 * (non-Javadoc)
	 * 
	 * @see java.lang.Thread#run()
	 */
	public void run() {
		boolean taskComplete=false;
		try {
			taskComplete=runTask();
		} catch (Exception e) {
			Alert al = new Alert("undefine exception", e.getMessage(), null,
					AlertType.ALARM);
			al.setTimeout(Alert.FOREVER);
			display.setCurrent(al);
		} finally {
			if (!taskComplete&&poUI.isStoppable()) {
				if (poUI.isStopped()) {//如果用户中断了程序
					if (needAlert) {
						display.setCurrent(alertScreen, preScreen);
					} else {
						display.setCurrent(preScreen);
					}
				}
			}
			poUI.exit();
		}
	}

	/**
	 * 须由用户定义的任务
	 * 注意!!!
	 * 任务如果成功的运行,应该由此方法内部负责跳转至成功画面,并返回true.
	 * 若任务运行失败,请设置needAlert(是否需要警报),AlertScreen(警报画面),preScreen(跳转回的前一个具体屏幕)
	 * 手动更新进度栏，请调用pgUI.updateProgress().
	 * 请确保当cancel()调用时,此方法会立即退出,并返回false(如果因为异常跳出此函数是可以接受的行为).
	 */
	public abstract boolean runTask();

	/**
	 * 这是一个偷懒的办法,当你构造好BackgroundTask对象后，直接调用这个方法， 可以帮助你初始化进度UI,并显示出来。之后启动你的任务线程
	 */
	public static void runWithProgressGauge(BackgroundTask btask, String title,
			String prompt, boolean stoppable, Display display) {
		ProgressObserver po = btask.getProgressObserver();
		po.reset();
		po.setStoppable(stoppable);
		if(stoppable){
			po.setCancelalbeObject(btask);
		}
		po.setTitle(title);
		po.setPrompt(prompt);
		po.show(display);
		btask.start();
	}

	public ProgressObserver getProgressObserver() {
		return poUI;
	}

	//取消了taskComplete方法,因为runTask已经有了返回值
//	
//	public void taskComplete(){
//		getProgressObserver().setStopped(false);
//	}
}