android中进度条的实现

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.example.administrator.progress.MainActivity">

    <ProgressBar
        android:id="@+id/progressBar"
        style="@android:style/Widget.ProgressBar.Horizontal"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />

</RelativeLayout>

package com.example.administrator.progress;

import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.widget.ProgressBar;

public class MainActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        final ProgressBar progressBar = (ProgressBar)findViewById(R.id.progressBar);
        final Handler handler = new Handler(){
            @Override
            public void handleMessage(Message msg) {
                super.handleMessage(msg);
                progressBar.setProgress(msg.what);
            }
        };
        final Thread thread = new Thread(){
            @Override
            public void run() {
                super.run();
                int index = 0;
                int numloop = 1;

                while (index < 100){
                    try {
                        Thread.sleep(100);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    handler.sendEmptyMessage(index);
                    index++;
                    if(index == 100){
                        while(index > 1){
                            try {
                                Thread.sleep(100);
                            } catch (InterruptedException e) {
                                e.printStackTrace();
                            }
                            handler.sendEmptyMessage(index);
                            index--;
                        }
                    }
                }
            }
        };
        thread.start();

    }
}