分享一下在工作中遇到的Android版本后台更新后自动安装的功能，在网上找了好多资料，然后自己修改，写了一个比较完整的版本。

一、判断当前版本号

//获取本地版本号
  public  String getVersion() {
    try {
          PackageManager manager =activity.getPackageManager();
          PackageInfo info =manager.getPackageInfo(activity.getPackageName(),0);
          String version = info.versionName;
          return version;
          }catch (Exception e) {
             e.printStackTrace();
             return "0";
          }
      }

接下来是本地版本号和服务器的版本号进行对比

  public  int compareVersion(String version1, String version2) {
    if (version1.equals(version2)) {
      return 0;
    }
    String[] version1Array = version1.split("\\.");
    String[] version2Array = version2.split("\\.");
    int index = 0;
    int minLen = Math.min(version1Array.length, version2Array.length);
    int diff = 0;
    while (index < minLen
      && (diff = Integer.parseInt(version1Array[index])
      - Integer.parseInt(version2Array[index])) == 0) {
      index++;
    }
    if (diff == 0) {
      for (int i = index; i < version1Array.length; i++) {
        if (Integer.parseInt(version1Array[i]) > 0) {
          return 1;
        }
      }
      for (int i = index; i < version2Array.length; i++) {
        if (Integer.parseInt(version2Array[i]) > 0) {
          return -1;
        }
      }
      return 0;
    } else {
      return diff > 0 ? 1 : -1;
    }
  }

二、创建一个更新服务的service

  public class UpdateService extends Service {
  public StringDOWNLOAD_PATH = Environment.getExternalStorageDirectory()                      +"/Download/Anxin.apk";
    private Stringurl;//下载链接
    private long refernece;
    private BroadcastReceiverreceiver;
    private IntentFilterfilter;
    public IBinder onBind(Intent arg0) {
      return null;
}

@Override
  public void onCreate() {
      super.onCreate();
}

@Override
  public int onStartCommand(Intent intent,int flags,int startId) {
    if (intent !=null) {
    url = intent.getStringExtra("Key_Down_Url");
    if (url !=null && !TextUtils.isEmpty(url)) {
    download(url);
      }
  }
    return super.onStartCommand(intent, flags, startId);
}

public void download(String url) {
    if (new File(DOWNLOAD_PATH).exists()) {
      new File(DOWNLOAD_PATH).delete();
    }
    receiver();
    DownloadManager dManager = (DownloadManager) getSystemService(Context.DOWNLOAD_SERVICE);
    Uri uri = Uri.parse(url);
    DownloadManager.Request request = new DownloadManager.Request(uri);
   request.setDestinationInExternalPublicDir(Environment.DIRECTORY_DOWNLOADS, "Anxin.apk");
    request.setDescription("新版本下载中...");
    request.setTitle("版本更新");
request.setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE_NOTIFY_COMPLETED);
    request.setMimeType("application/vnd.android.package-archive");
    // 设置为可被媒体扫描器
    request.allowScanningByMediaScanner();
    // 设置为可见
    request.setVisibleInDownloadsUi(true);
    try {
      refernece = dManager.enqueue(request);
    } catch (Exception e) {
    }
  }

  public void receiver() {
    filter = new IntentFilter(DownloadManager.ACTION_DOWNLOAD_COMPLETE);
    receiver = new BroadcastReceiver() {
      public void onReceive(Context context, Intent intent) {
        long myDwonloadID = intent.getLongExtra(DownloadManager.EXTRA_DOWNLOAD_ID, -1);
        if (refernece == myDwonloadID) {
          DownloadManager dManager = (DownloadManager)getSystemService(Context.DOWNLOAD_SERVICE);
          setPermission(DOWNLOAD_PATH);
          Intent install = new Intent(Settings.ACTION_MANAGE_UNKNOWN_APP_SOURCES, Uri.parse("package:" + getPackageName()));
          install.setAction(Intent.ACTION_VIEW);
          install.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
          install.addCategory(Intent.CATEGORY_DEFAULT);
          if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N) {//大于Android版本7.0
            //这里的"com.anxin.provider"需要和AndroidManifest.xml的provider属性保持一致
            Uri contentUri = FileProvider.getUriForFile(context, "com.anxin.provider", new File(DOWNLOAD_PATH));
            install.addFlags(Intent.FLAG_GRANT_READ_URI_PERMISSION);
            install.setDataAndType(contentUri, "application/vnd.android.package-archive");
            context.startActivity(install);
          } else {
            try {
              Uri downloadFileUri = dManager.getUriForDownloadedFile(refernece);
              install.setDataAndType(downloadFileUri.fromFile(new File(DOWNLOAD_PATH)), "application/vnd.android.package-archive");
              context.startActivity(install);
            } catch (RuntimeException e) {
              e.printStackTrace();
            }
          }
        }
      }
    };
    registerReceiver(receiver, filter);
  }

 /**
   * 提升读写权限
   *
   * @param filePath 文件路径
   */
    public static void setPermission(String filePath) {
    String command ="chmod " +"777" +" " + filePath;
    Runtime runtime = Runtime.getRuntime();
    try {
        runtime.exec(command);
    }catch (IOException e) {
        e.printStackTrace();
      }
  }

  public void onDestroy() {
    unregisterReceiver(receiver);
  }
}

三、接下来就是通过弹框进行更新

    public void AlertDialog2() {
       mDialog =new Dialog(SheZhiActivity.this, R.style.mydialog);
       View view = View.inflate(SheZhiActivity.this, R.layout.view_dialog,null);
       mDialog.setContentView(view);
       TextView UpdateContent = (TextView)view.findViewById(R.id.UpdateContent);
       UpdateContent.setText(downContent);
       TextView UpdateVersion = (TextView)view.findViewById(R.id.UpdateVersion);
       UpdateVersion.setText("V"+newVersion);
       mDialog.getWindow().findViewById(R.id.UpdateNow).setOnClickListener(new View.OnClickListener() {
    @Override
       public void onClick(View v) {
       Intent intent =new Intent(SheZhiActivity.this, UpdateService.class);
       intent.putExtra("Key_Down_Url",downUrl);
       startService(intent);
       Toast.makeText(getApplicationContext(),"后台更新下载中...",  Toast.LENGTH_SHORT).show();
       mDialog.dismiss();
    }
});
       mDialog.show();
}

四、需要在AndroidManifest.xml中添加provider

   <provider
      android:name="android.support.v4.content.FileProvider"
      android:authorities="com.anxin.provider"
      android:exported="false"
      android:grantUriPermissions="true">
      <meta-data
        android:name="android.support.FILE_PROVIDER_PATHS"
        android:resource="@xml/file_paths" />
    </provider>

五、总结

在android版本6.0之前和之后的安装方式是不同的，需要注意一下。最后别忘了在AndroidManifest.xml中添加各种权限。