Android AsyncTask 异步任务操作

<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);
        }
    }
}