android.os.NetworkOnMainThreadException与android 4.2

Question

在这里，我使用此代码加载Json。它做工精细的Android 2.2，但是当我使用的Android 4.2，它抛出android.os.NetworkOnMainThreadException例外，请给我解决

public class JSONParser { 

    static InputStream is = null; 

static JSONObject jObj = null; 
static String json = ""; 

// constructor 
public JSONParser() { 

} 

public JSONObject getJSONFromUrl(String url) { 

    // Making HTTP request 
    try { 
     // defaultHttpClient 
     DefaultHttpClient httpClient = new DefaultHttpClient(); 
     HttpGet httpPost = new HttpGet(url); 

      HttpResponse getResponse = httpClient.execute(httpPost); 
      final int statusCode = getResponse.getStatusLine().getStatusCode(); 

      if (statusCode != HttpStatus.SC_OK) { 
       Log.w(getClass().getSimpleName(), 
        "Error " + statusCode + " for URL " + url); 
       return null; 
      } 

      HttpEntity getResponseEntity = getResponse.getEntity(); 

     //HttpResponse httpResponse = httpClient.execute(httpPost); 
     //HttpEntity httpEntity = httpResponse.getEntity(); 
     is = getResponseEntity.getContent();    

    } catch (UnsupportedEncodingException e) { 
     e.printStackTrace(); 
    } catch (ClientProtocolException e) { 
     e.printStackTrace(); 
    } catch (IOException e) { 
     Log.d("IO", e.getMessage().toString()); 
     e.printStackTrace(); 

    } 

    try { 
     BufferedReader reader = new BufferedReader(new InputStreamReader(
       is, "iso-8859-1"), 8); 
     StringBuilder sb = new StringBuilder(); 
     String line = null; 
     while ((line = reader.readLine()) != null) { 
      sb.append(line + "\n"); 
     } 
     is.close(); 
     json = sb.toString(); 
    } catch (Exception e) { 
     Log.e("Buffer Error", "Error converting result " + e.toString()); 
    } 

    // try parse the string to a JSON object 
    try { 
     jObj = new JSONObject(json); 
    } catch (JSONException e) { 
     Log.e("JSON Parser", "Error parsing data " + e.toString()); 
    } 

    // return JSON String 
    return jObj; 

} 

}

我也使用谷歌API。

Answer 1

在setContentView（R.layout.activity_main）之后将代码写入您的MainActivity文件中;

if (android.os.Build.VERSION.SDK_INT > 9) { 
    StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build(); 
    StrictMode.setThreadPolicy(policy); 
} 

和下面的import语句放到你的java文件中。

import android.os.StrictMode; 

Answer 2

请确保你不这样做的UI线程任何网络访问，而不是做在Async Task

之所以在Android 3.0及以上版本，您的应用程序崩溃，但能正常工作在Android 2.X是因为HoneyComb对UI线程的滥用要严格得多。例如，当运行HoneyComb或更高版本的Android设备检测到UI线程上的网络访问时，将引发NetworkOnMainThreadException。

见当您尝试访问网络上的主线程（您的主要活动执行）发生this

Answer 3

android.os.NetworkOnMainThreadException。为了避免这种情况，您必须创建一个单独的线程或AsyncTask或Runnable实现来执行您的JSON数据加载。由于HoneyComb不能在主线程上进一步执行网络任务。 Here是使用AsyncTask执行网络任务的实现

Answer 4

使用StrictMode事情是这样的： -

if (android.os.Build.VERSION.SDK_INT > 9) { 
     StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build(); 

     StrictMode.setThreadPolicy(policy); 
     } 

Answer 5

这是正确的做法：

public class JSONParser extends AsyncTask <String, Void, String>{ 

    static InputStream is = null; 

static JSONObject jObj = null; 
static String json = ""; 

// constructor 
public JSONParser() { 

} 
@Override 
protected String doInBackground(String... params) { 


    // Making HTTP request 
    try { 
     // defaultHttpClient 
     DefaultHttpClient httpClient = new DefaultHttpClient(); 
     HttpGet httpPost = new HttpGet(url); 

      HttpResponse getResponse = httpClient.execute(httpPost); 
      final int statusCode = getResponse.getStatusLine().getStatusCode(); 

      if (statusCode != HttpStatus.SC_OK) { 
       Log.w(getClass().getSimpleName(), 
        "Error " + statusCode + " for URL " + url); 
       return null; 
      } 

      HttpEntity getResponseEntity = getResponse.getEntity(); 

     //HttpResponse httpResponse = httpClient.execute(httpPost); 
     //HttpEntity httpEntity = httpResponse.getEntity(); 
     is = getResponseEntity.getContent();    

    } catch (UnsupportedEncodingException e) { 
     e.printStackTrace(); 
    } catch (ClientProtocolException e) { 
     e.printStackTrace(); 
    } catch (IOException e) { 
     Log.d("IO", e.getMessage().toString()); 
     e.printStackTrace(); 

    } 

    try { 
     BufferedReader reader = new BufferedReader(new InputStreamReader(
       is, "iso-8859-1"), 8); 
     StringBuilder sb = new StringBuilder(); 
     String line = null; 
     while ((line = reader.readLine()) != null) { 
      sb.append(line + "\n"); 
     } 
     is.close(); 
     json = sb.toString(); 
    } catch (Exception e) { 
     Log.e("Buffer Error", "Error converting result " + e.toString()); 
    } 

    // try parse the string to a JSON object 
    try { 
     jObj = new JSONObject(json); 
    } catch (JSONException e) { 
     Log.e("JSON Parser", "Error parsing data " + e.toString()); 
    } 

    // return JSON String 
    return jObj; 


} 
protected void onPostExecute(String page) 
{ 
    //onPostExecute 
} 
} 

要调用它（从主）：

mJSONParser = new JSONParser(); 
mJSONParser.execute();