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 documentDesigning for Responsiveness.

Also seeStrictMode.

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。

[java] view plain copy print ?

publicvoidonCreate(BundlesavedInstanceState){
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
newThread(networkTask).start();
}
Handlerhandler=newHandler(){
@Override
publicvoidhandleMessage(Messagemsg){
super.handleMessage(msg);
Bundledata=msg.getData();
Stringval=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
*/
RunnablenetworkTask=newRunnable(){
@Override
publicvoidrun(){
//TODO
//在这里进行httprequest.网络请求相关操作
Messagemsg=newMessage();
Bundledata=newBundle();
data.putString("value","请求结果");
msg.setData(data);
handler.sendMessage(msg);
}
};

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UInew Thread(networkTask).start();}Handler handler = new Handler() {@Overridepublic 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() {@Overridepublic 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

[java] view plain copy print ?

classDownImageextendsAsyncTask{
privateImageViewimageView;
publicDownImage(ImageViewimageView){
this.imageView=imageView;
}
@Override
protectedBitmapdoInBackground(String...params){
Stringurl=params[0];
Bitmapbitmap=null;
try{
//加载一个网络图片
InputStreamis=newURL(url).openStream();
bitmap=BitmapFactory.decodeStream(is);
}catch(Exceptione){
e.printStackTrace();
}
returnbitmap;
}
@Override
protectedvoidonPostExecute(Bitmapresult){
imageView.setImageBitmap(result);
}
}

class DownImage extends AsyncTask {private ImageView imageView;public DownImage(ImageView imageView) {this.imageView = imageView;}@Overrideprotected 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;}@Overrideprotected 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：

[java] view plain copy print ?

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

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

请记住，如果在Main Thread里声明了一个handler，这个handler所Post 的 Runnable（Thread）、以及处理的message都是在当前的mian线程里，非子线程。

Class Overview

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