<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"

    xmlns:tools="http://schemas.android.com/tools"

    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=".MainActivity" >

    <TextView

        android:id="@+id/tvInfo"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:text="@string/hello_world" />

    <ProgressBar

         android:layout_below="@id/tvInfo"

         android:id="@+id/asyncPb"

         style="?android:attr/progressBarStyleHorizontal"

         android:layout_width="fill_parent"

         android:layout_height="wrap_content"

         android:visibility="gone"

         />  

</RelativeLayout>

package com.example.async;

import android.os.AsyncTask;

import android.os.Bundle;

import android.view.View;

import android.widget.ProgressBar;

import android.widget.TextView;

import android.app.Activity;

public class MainActivity extends Activity {

    private ProgressBar asyncPb = null;

    private TextView tvInfo = null;

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        tvInfo = (TextView)findViewById(R.id.tvInfo);

        String params = "Welcome to here";

        new MyAsyncTask().execute(params);

    }

    private class MyAsyncTask extends AsyncTask<String, Integer, String>{

        @Override

        protected void onPreExecute() {

            //做一些预处理

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

            asyncPb.setVisibility(View.VISIBLE);

        }

        @Override

        protected String doInBackground(String... params) {

            //执行耗时操作，网络任务、文件操作、数据库操作、复杂计算操作

            int myProgress = 0;

            int length = params[0].length();

            for(int i=1; i<=length; i++){

                myProgress = i;

                //模拟耗时操作

                try {

                    Thread.sleep(300);

                } catch (InterruptedException e) {

                    e.printStackTrace();

                }

                publishProgress((int)((myProgress/(float)length)*100));

            }

            //它将传递给onPostExecute

            return params[0];

        }

        @Override

        protected void onProgressUpdate(Integer... values) {

            //更新进度条

            asyncPb.setProgress(values[0]);

            tvInfo.setText("已加载："+(values[0])+"%");

        }

        @Override

        protected void onPostExecute(String result) {

            //更新UI

            tvInfo.setText("加载完成："+result);

        }

    }

}