Android ProgressBar 进度条

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
>
<ProgressBar
android:id="@+id/pb"
android:layout_marginLeft="10sp"
android:layout_width="300sp"
android:layout_height="20sp"
android:layout_marginTop="10sp"
style="?android:attr/progressBarStyleHorizontal"
/>
<Button
android:id = "@+id/startButton"
android:layout_marginTop="10sp"
android:layout_marginLeft="20sp"
android:layout_width="150sp"
android:layout_height="40sp"
android:text="Start"
/>
<Button
android:id = "@+id/endButton"
android:layout_marginTop="10sp"
android:layout_marginLeft="20sp"
android:layout_width="150sp"
android:layout_height="40sp"
android:text="End"
/>
</LinearLayout>

package nyl.pbdemo;

import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.ProgressBar;

public class Main extends Activity {
private Button startButton;
private Button endButton;
private ProgressBar pb;
private int process_value = 500;

//创建Handler对象
private Handler handler = new Handler();

@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);

//根据id获得控件对象
startButton = (Button)findViewById(R.id.startButton);
endButton = (Button)findViewById(R.id.endButton);

//为控件设置监听器
startButton.setOnClickListener(new StartButtonListener());
endButton.setOnClickListener(new EndButtonListener());

pb = (ProgressBar) findViewById(R.id.pb);

//设置初始值和最大值
pb.setProgress(500);
pb.setMax(pb.getMax());
}

class StartButtonListener implements OnClickListener{
@Override
public void onClick(View v) {
//调用Handler的post()方法，将要执行的线程对象放到队列当中
handler.post(updateThread);
}
}

class EndButtonListener implements OnClickListener{
@Override
public void onClick(View v) {
//调用Handler的removeCallbacks()方法，删除队列当中未执行的线程对象
handler.removeCallbacks(updateThread);
}
}

//新建一个线程对象
Runnable updateThread = new Runnable(){
//将要执行的操作写在线程对象的run方法当中
public void run() {
if (pb.getProgress() > 0) {
//进度条的值
process_value -= 1;
pb.setProgress(process_value);
}

//调用Handler的postDelayed()方法
//这个方法的作用是：将要执行的线程对象放入到队列当中，待时间结束后，运行制定的线程对象
//第一个参数是Runnable类型：将要执行的线程对象
//第二个参数是long类型：延迟的时间，以毫秒为单位
handler.postDelayed(updateThread, 200);
}
};
}