自動更新功能的實(shí)現(xiàn)原理，就是我們事先和后臺協(xié)商好一個接口，我們在應(yīng)用的主Activity里，去訪問這個接口，如果需要更新，后臺會返回一些數(shù)據(jù)(比如，提示語；最新版本的url等)。然后我們給出提示框，用戶點(diǎn)擊開始下載，下載完成開始覆蓋安裝程序，這樣用戶的應(yīng)用就保持最新的拉。

為了讓大家容易理解，我像往常一樣準(zhǔn)備一個小例子，這里為了方便我就省去了和后臺交互部分了。步驟分別如下：

第一步：新建一個Android工程命名為:UpdateDemo.代碼結(jié)構(gòu)如下圖所示

第二步：新建一個UpdateManager.java類，負(fù)責(zé)軟件更新功能模塊，代碼如下：

package com.tutor.update; 
 
import java.io.File; 
import java.io.FileOutputStream; 
import java.io.IOException; 
import java.io.InputStream; 
import java.net.HttpURLConnection; 
import java.net.MalformedURLException; 
import java.net.URL; 
 
 
import android.app.AlertDialog; 
import android.app.Dialog; 
import android.app.AlertDialog.Builder; 
import android.content.Context; 
import android.content.DialogInterface; 
import android.content.Intent; 
import android.content.DialogInterface.OnClickListener; 
import android.net.Uri; 
import android.os.Handler; 
import android.os.Message; 
import android.view.LayoutInflater; 
import android.view.View; 
import android.widget.ProgressBar; 
 
public class UpdateManager { 
 
 private Context mContext; 
  
 //提示語 
 private String updateMsg = "有最新的軟件包哦，親快下載吧~"; 
  
 //返回的安裝包url 
 private String apkUrl = "http://softfile.3g.qq.com:8080/msoft/179/24659/43549/qq_hd_mini_1.4.apk"; 
  
  
 private Dialog noticeDialog; 
  
 private Dialog downloadDialog; 
  /* 下載包安裝路徑 */ 
 private static final String savePath = "/sdcard/updatedemo/"; 
  
 private static final String saveFileName = savePath + "UpdateDemoRelease.apk"; 
 
 /* 進(jìn)度條與通知ui刷新的handler和msg常量 */ 
 private ProgressBar mProgress; 
 
  
 private static final int DOWN_UPDATE = 1; 
  
 private static final int DOWN_OVER = 2; 
  
 private int progress; 
  
 private Thread downLoadThread; 
  
 private boolean interceptFlag = false; 
  
 private Handler mHandler = new Handler(){ 
  public void handleMessage(Message msg) { 
   switch (msg.what) { 
   case DOWN_UPDATE: 
    mProgress.setProgress(progress); 
    break; 
   case DOWN_OVER: 
     
    installApk(); 
    break; 
   default: 
    break; 
   } 
  }; 
 }; 
  
 public UpdateManager(Context context) { 
  this.mContext = context; 
 } 
  
 //外部接口讓主Activity調(diào)用 
 public void checkUpdateInfo(){ 
  showNoticeDialog(); 
 } 
  
  
 private void showNoticeDialog(){ 
  AlertDialog.Builder builder = new Builder(mContext); 
  builder.setTitle("軟件版本更新"); 
  builder.setMessage(updateMsg); 
  builder.setPositiveButton("下載", new OnClickListener() {   
   @Override 
   public void onClick(DialogInterface dialog, int which) { 
    dialog.dismiss(); 
    showDownloadDialog();    
   } 
  }); 
  builder.setNegativeButton("以后再說", new OnClickListener() {    
   @Override 
   public void onClick(DialogInterface dialog, int which) { 
    dialog.dismiss();     
   } 
  }); 
  noticeDialog = builder.create(); 
  noticeDialog.show(); 
 } 
  
 private void showDownloadDialog(){ 
  AlertDialog.Builder builder = new Builder(mContext); 
  builder.setTitle("軟件版本更新"); 
   
  final LayoutInflater inflater = LayoutInflater.from(mContext); 
  View v = inflater.inflate(R.layout.progress, null); 
  mProgress = (ProgressBar)v.findViewById(R.id.progress); 
   
  builder.setView(v); 
  builder.setNegativeButton("取消", new OnClickListener() { 
   @Override 
   public void onClick(DialogInterface dialog, int which) { 
    dialog.dismiss(); 
    interceptFlag = true; 
   } 
  }); 
  downloadDialog = builder.create(); 
  downloadDialog.show(); 
   
  downloadApk(); 
 } 
  
 private Runnable mdownApkRunnable = new Runnable() {  
  @Override 
  public void run() { 
   try { 
    URL url = new URL(apkUrl); 
    
    HttpURLConnection conn = (HttpURLConnection)url.openConnection(); 
    conn.connect(); 
    int length = conn.getContentLength(); 
    InputStream is = conn.getInputStream(); 
     
    File file = new File(savePath); 
    if(!file.exists()){ 
     file.mkdir(); 
    } 
    String apkFile = saveFileName; 
    File ApkFile = new File(apkFile); 
    FileOutputStream fos = new FileOutputStream(ApkFile); 
     
    int count = 0; 
    byte buf[] = new byte[1024]; 
     
    do{     
     int numread = is.read(buf); 
     count += numread; 
     progress =(int)(((float)count / length) * 100); 
     //更新進(jìn)度 
     mHandler.sendEmptyMessage(DOWN_UPDATE); 
     if(numread <= 0){  
      //下載完成通知安裝 
      mHandler.sendEmptyMessage(DOWN_OVER); 
      break; 
     } 
     fos.write(buf,0,numread); 
    }while(!interceptFlag);//點(diǎn)擊取消就停止下載. 
     
    fos.close(); 
    is.close(); 
   } catch (MalformedURLException e) { 
    e.printStackTrace(); 
   } catch(IOException e){ 
    e.printStackTrace(); 
   } 
    
  } 
 }; 
  
  /** 
  * 下載apk 
  * @param url 
  */ 
  
 private void downloadApk(){ 
  downLoadThread = new Thread(mdownApkRunnable); 
  downLoadThread.start(); 
 } 
  /** 
  * 安裝apk 
  * @param url 
  */ 
 private void installApk(){ 
  File apkfile = new File(saveFileName); 
  if (!apkfile.exists()) { 
   return; 
  }  
  Intent i = new Intent(Intent.ACTION_VIEW); 
  i.setDataAndType(Uri.parse("file://" + apkfile.toString()), "application/vnd.android.package-archive"); 
  mContext.startActivity(i); 
  
 } 
}

第三步：在MainActivity.java也就是主Activity調(diào)用,代碼如下：

package com.tutor.update; 
 
import android.app.Activity; 
import android.os.Bundle; 
 
public class MainAcitivity extends Activity { 
  
 
 private UpdateManager mUpdateManager; 
 @Override 
 public void onCreate(Bundle savedInstanceState) { 
  super.onCreate(savedInstanceState); 
  setContentView(R.layout.main); 
   
  //這里來檢測版本是否需要更新 
  mUpdateManager = new UpdateManager(this); 
  mUpdateManager.checkUpdateInfo(); 
 }  
}

第四步：添加程序所用的資源與權(quán)限：
下載的時候用到了ProgressBar,所以事先寫了一個progress.xml布局文件，代碼如下:

<?xml version="1.0" encoding="utf-8"?> 
<LinearLayout 
 xmlns:android="http://schemas.android.com/apk/res/android" 
 android:layout_width="fill_parent" 
 android:layout_height="wrap_content"> 
 
 <ProgressBar 
 android:id="@+id/progress" 
 android:layout_width="fill_parent" 
 android:layout_height="wrap_content" 
 style="?android:attr/progressBarStyleHorizontal" 
 /> 
</LinearLayout>

下載的時候用到了網(wǎng)絡(luò)部分，所以要在AndroidManifest.xml中添加網(wǎng)絡(luò)權(quán)限，代碼如下:
<uses-permission android:name="android.permission.INTERNET" />

第五步：運(yùn)行查看效果如下：