使用AsyncTask实现文件下载并且在状态中显示下载进度

2013年10月24日　　上班的第二天

　　昨天我是用afinal完成的则个功能，但是公司里并不希望使用第三方的代码，所以要求我在不使用第三方开源项目的情况下实现。

　

　　最先我是使用Thread开启一个子线程，在这个线程中完成文件下载，然后使用Handler异步消息来更新Notification中的进度条，废了九牛二虎之力，虽然完成了功能，但是做出的效果就是特别的卡，甚至连通知栏下拉都被冻结了。

　　后来我尝试了AsyncTask，很轻松的完成了下载和进度值的计算，但是在通知栏中改变进度条的进度，依然会出现卡屏的问题。

　　最后在StackOverFlow中查找解决方案，给出的答案是，在更新Notification的时候，使用Handler来更新进度条进度，更新的频率特别高，再次期间会不断的生成RemoteViews对象，所以消耗了大量的内存。虽然没有看到实实在在的代码，但是有了解决的思路。

　　1.降低Handler的更新的频率；

　　2.尽量能够复用RemoteViews的对象。

　　

　　对应的具体的实现是用计数器来控制更新的频率，用静态的RemoteViews对象。

　　

　　后面上代码：

　　主界面的布局文件：activity_main.xml

 <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:padding="10dp"
     tools:context=".MainActivity" >

     <TextView
         android:id="@+id/hint_tv"
         android:layout_width="wrap_content"
         android:layout_height="wrap_content"
         android:paddingTop="10dp"
         android:text="@string/tv_main_hint" />

     <EditText
         android:id="@+id/url_et"
         android:layout_width="match_parent"
         android:layout_height="wrap_content"
         android:layout_toRightOf="@id/hint_tv"
         android:hint="@string/et_downloadurl"
         android:singleLine="true" />

     <Button
         android:id="@+id/downloadBtn"
         android:layout_width="match_parent"
         android:layout_height="wrap_content"
         android:layout_below="@id/url_et"
         android:paddingTop="20dp"
         android:text="@string/str_download" />

      <Button
          android:layout_below="@id/downloadBtn"
         android:id="@+id/pauseBtn"
         android:layout_width="match_parent"
         android:layout_height="wrap_content"
         android:paddingTop="20dp"
         android:text="@string/btn_pause" />

      <Button
          android:layout_below="@id/pauseBtn"
         android:id="@+id/continueBtn"
         android:layout_width="match_parent"
         android:layout_height="wrap_content"
         android:paddingTop="20dp"
         android:text="@string/btn_continue" />

      <ProgressBar
          android:layout_below="@id/continueBtn"
         android:id="@+id/pb"
         style="?android:attr/progressBarStyleHorizontal"
         android:layout_width="match_parent"
         android:layout_height="wrap_content"
         android:paddingTop="20dp" />

      <TextView
          android:layout_below="@id/pb"
         android:id="@+id/progressTV"
         android:text="0%"
         android:layout_centerHorizontal="true"
         android:layout_width="wrap_content"
         android:layout_height="wrap_content"
         android:paddingTop="20dp" />

 </RelativeLayout>

自定义Notification的布局文件： notify_vew.xml

 <?xml version="1.0" encoding="utf-8"?>
 <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
     android:layout_width="fill_parent"
     android:layout_height="fill_parent" >

     <ImageView
         android:id="@+id/notify_icon"
         android:layout_width="wrap_content"
         android:layout_height="wrap_content"
         android:src="@drawable/ic_launcher" />

     <TextView
         android:id="@+id/tv"
         android:layout_width="wrap_content"
         android:layout_height="wrap_content"
         android:layout_toRightOf="@id/notify_icon"
         android:singleLine="true"
         android:text="下载进度..." />

     <ProgressBar
         android:id="@+id/pb"
         style="?android:attr/progressBarStyleHorizontal"
         android:layout_width="match_parent"
         android:layout_height="wrap_content"
         android:layout_below="@id/tv"
         android:layout_toRightOf="@id/notify_icon"
         android:max="100"
         android:paddingRight="10dp"
         android:progress="50"
         android:secondaryProgress="74"
         android:visibility="visible" />

 </RelativeLayout>

strings.xml

 <?xml version="1.0" encoding="utf-8"?>
 <resources>

     <string name="app_name">DownLoader</string>
     <string name="action_settings">Settings</string>
     <string name="hello_world">Hello world!</string>
     <string name="tv_main_hint">下载地址：</string>
     <string name="et_downloadurl">请输入下载地址</string>
     <string name="str_download">开始下载</string>
     <string name="btn_pause">暂停下载</string>
     <string name="btn_continue">继续下载</string>

 </resources>

在清单文件中申请的权限：AndroidManifest.xml

 <uses-permission android:name="android.permission.INTERNET"/>
     <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>

MainActivity.java

 package com.yt.asynctaskdemo;

 import java.io.FileOutputStream;

 import java.io.IOException;
 import java.io.InputStream;
 import java.io.OutputStream;
 import java.net.MalformedURLException;
 import java.net.URL;
 import java.net.URLConnection;

 import android.os.AsyncTask;
 import android.os.Bundle;
 import android.os.Environment;
 import android.os.Handler;
 import android.os.Message;
 import android.app.Activity;
 import android.app.Notification;
 import android.app.NotificationManager;
 import android.app.PendingIntent;
 import android.content.Context;
 import android.content.Intent;
 import android.util.Log;
 import android.view.View;
 import android.view.View.OnClickListener;
 import android.widget.Button;
 import android.widget.EditText;
 import android.widget.ProgressBar;
 import android.widget.RemoteViews;
 import android.widget.TextView;

 public class MainActivity extends Activity {

     public static final String TAG = "MainActivity";

     private int count;
     private int current;
     private EditText downloadUrlEt;
     private Button downloadBtn;
     private Button pauseBtn;
     private Button continueBtn;
     private ProgressBar pb;
     private int progress;
     private TextView progressTV;
     private boolean finished;
     private boolean paused;
     private NotificationManager manager;
     private Notification notification;
     private static RemoteViews contentView;

     private int times;

     private MyAsyncTask mTask;

     private Handler handler = new Handler(){
         public void handleMessage(android.os.Message msg) {
             if(contentView == null){
                 contentView = new RemoteViews(getPackageName(), R.layout.notify_view);
                 contentView.setProgressBar(R.id.pb, 100, 0, false);
                 notification.icon = R.drawable.ic_launcher;
                 notification.tickerText = "下载进度";
                 notification.flags = notification.DEFAULT_ALL;
                 notification.contentView = contentView;
                 PendingIntent contentIntent = PendingIntent.getActivity(MainActivity.this, 0,
                         new Intent(MainActivity.this, MainActivity.class), 0);

                 notification.setLatestEventInfo(MainActivity.this, "你好！",
                                "byebye", contentIntent);
                 manager.notify(0, notification);
             }
             if(times++ % 5 == 0 || progress==100){
                 contentView.setProgressBar(R.id.pb, 100, progress, false);
                 notification.contentView = contentView;
                 manager.notify(0, notification);
             }
             super.handleMessage(msg);
         };
     };
     @Override
     protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         setContentView(R.layout.activity_main);
         downloadUrlEt = (EditText) findViewById(R.id.url_et);
         downloadUrlEt.setText("http://mit.95195.com/singleonline.apk");
         downloadBtn = (Button) findViewById(R.id.downloadBtn);
         pauseBtn = (Button) findViewById(R.id.pauseBtn);
         continueBtn = (Button) findViewById(R.id.continueBtn);
         progressTV = (TextView) findViewById(R.id.progressTV);
         pb = (ProgressBar) findViewById(R.id.pb);
         MyOnClickListener listener = new MyOnClickListener();
         downloadBtn.setOnClickListener(listener);
         pauseBtn.setOnClickListener(listener);
         continueBtn.setOnClickListener(listener);
         mTask = new MyAsyncTask();
         manager = (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);
         notification = new Notification(R.drawable.ic_launcher, "下载进度条...",System.currentTimeMillis());
     }

     /**
      * 按钮事件监听
      *
      * @author yt
      *
      */
     class MyOnClickListener implements OnClickListener {

         @Override
         public void onClick(View v) {
             switch (v.getId()) {
             case R.id.downloadBtn:
                 mTask.execute("http://mit.95195.com/singleonline.apk");
                 break;

             case R.id.pauseBtn:
                 paused = true;
                 break;

             case R.id.continueBtn:
                 paused = false;
                 break;
             }
         }

     }

     class MyAsyncTask extends AsyncTask<String, Integer, String>{
         @Override
         protected String doInBackground(String... params) {
             try {
                 URL url = new URL(params[0]);
                 URLConnection conn = url.openConnection();
                 count = conn.getContentLength();
                 InputStream is = conn.getInputStream();
                 OutputStream os = new FileOutputStream(Environment.getExternalStorageDirectory()+"/singleon.apk");
                 byte[] buffer = new byte[1024];
                 int len = -1;
                 while(!finished){
                     while(!paused && (len = is.read(buffer))>0){
                             current += len;
                             os.write(buffer,0,len);
                             progress = current * 100 / count;
 //                            Log.i(TAG, "current = " + current + " count = " + count + " progress = " + progress);
                             publishProgress(progress);
                             Message msg = new Message();
                             handler.handleMessage(msg);
                     }
                 }

             } catch (MalformedURLException e) {
                 e.printStackTrace();
             } catch (IOException e) {;
                 e.printStackTrace();
             }

             return progress+"";
         }    

         @Override
         protected void onPostExecute(String result) {
             Log.i(TAG, result+"");
             super.onPostExecute(result);
         }

         @Override
         protected void onProgressUpdate(Integer... values) {

             if(values[0]==99){
                 finished = true;
                 manager.cancel(0);
             }
             progressTV.setText(values[0]+"");
             pb.setProgress(progress);
             super.onProgressUpdate(values);
         }

         @Override
         protected void onPreExecute() {
             handler.handleMessage(new Message());
             super.onPreExecute();
         }

     }

 }

完整代码下载：http://download.csdn.net/detail/yuan936845015/6450041