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[操作系统]Android之NetworkOnMainThreadException异常


看名字就应该知道,是网络请求在MainThread中产生的异常

 

先来看一下官网的解释:

 

Class Overview

The exception that is thrown when an application attempts to perform a networking operation on its main thread.

This is only thrown for applications targeting the Honeycomb SDK or higher. Applications targeting earlier SDK versions are allowed to do networking on their main event loop threads, but it's heavily discouraged. See the document Designing for Responsiveness.

Also see StrictMode.

http://developer.android.com/intl/zh-cn/reference/android/os/NetworkOnMainThreadException.html

 

解释一下,从Honeycomb SDK(3.0)开始,google不再允许网络请求(HTTP、Socket)等相关操作直接在Main Thread类中,其实本来就不应该这样做,直接在UI线程进行网络操作,会阻塞UI、用户体验相当bad!即便google不禁止,一般情况下我们也不会这么做吧~

所以,也就是说,在Honeycomb SDK(3.0)以下的版本,你还可以继续在Main Thread里这样做,在3.0以上,就不行了,建议

 

1,和network有关比较耗时的操作放到一个子线程里,然后用Handler消息机制与主线程通信。

  public void onCreate(Bundle savedInstanceState) {    super.onCreate(savedInstanceState);    this.setContentView(R.layout.test);    // 开启一个子线程,进行网络操作,等待有返回结果,使用handler通知UI    new Thread(networkTask).start();  }  Handler handler = new Handler() {    @Override    public void handleMessage(Message msg) {      super.handleMessage(msg);      Bundle data = msg.getData();      String val = data.getString("value");      Log.i("mylog", "请求结果为-->" + val);      // TODO      // UI界面的更新等相关操作    }  };  /**   * 网络操作相关的子线程   */  Runnable networkTask = new Runnable() {    @Override    public void run() {      // TODO      // 在这里进行 http request.网络请求相关操作      Message msg = new Message();      Bundle data = new Bundle();      data.putString("value", "请求结果");      msg.setData(data);      handler.sendMessage(msg);    }  };

2,使用异步机制如:asynctask,这个举个简单的加载网络图片的例子

class DownImage extends AsyncTask {  private ImageView imageView;  public DownImage(ImageView imageView) {    this.imageView = imageView;  }  @Override  protected Bitmap doInBackground(String... params) {    String url = params[0];    Bitmap bitmap = null;    try {      //加载一个网络图片      InputStream is = new URL(url).openStream();      bitmap = BitmapFactory.decodeStream(is);    } catch (Exception e) {      e.printStackTrace();    }    return bitmap;  }  @Override  protected void onPostExecute(Bitmap result) {    imageView.setImageBitmap(result);  }}

3,直接在main Thread 进行网络操作的方法,网上给出的,我没有具体测试:

在发起Http请求的Activity里面的onCreate函数里面添加如下代码:

    StrictMode.setThreadPolicy(new StrictMode.ThreadPolicy.Builder().detectDiskReads().detectDiskWrites().detectNetwork().penaltyLog().build());    StrictMode.setVmPolicy(new StrictMode.VmPolicy.Builder().detectLeakedSqlLiteObjects().detectLeakedClosableObjects().penaltyLog().penaltyDeath().build());

 from:Never-say-Never