Android HTTP Post返回null

Question

我有一个异步任务，不断向服务器发送消息并接收消息作为回报。当我测试它时，我让它运行几秒钟，然后关掉wifi。该应用程序然后崩溃并发送空指针异常。我能够在HTTPPost中做任何事情，或者只是在没有互联网而不是崩溃应用程序的情况下发送消息？

这是我的代码

private class UpdateLoc extends AsyncTask<Void,Void,String> { 
     InputStream inputStream = null; 
     @Override 
     protected void onPreExecute() { 
      super.onPreExecute(); 
     } 

     @Override 
     protected void onPostExecute(String s) { 
      super.onPostExecute(s); 
      try{ 
       if(s.trim()!=null){ 
        Log.d("HTTPRESULT",s.toString()); 
       } 
      }catch (Exception e){ 
       e.printStackTrace(); 
      } 

     } 

     @Override 
     protected String doInBackground(Void... params) { 
      String result = null; 
      HttpClient httpClient = new DefaultHttpClient(); 
      HttpPost httpPost = new HttpPost(Constants.UPDATE); 
      List<NameValuePair> nameValuePairs = new ArrayList<>(); 
      nameValuePairs.add(new BasicNameValuePair(Constants.params_email,email)); 
      nameValuePairs.add(new BasicNameValuePair(Constants.params_location,curr_location)); 

      try{ 
       httpPost.setEntity(new UrlEncodedFormEntity(nameValuePairs)); 
       HttpResponse httpResponse = httpClient.execute(httpPost); 
       HttpEntity httpEntity = httpResponse.getEntity(); 
       inputStream = httpEntity.getContent(); 

       BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream,"UTF-8"),8); 
       StringBuilder stringBuilder = new StringBuilder(); 
       String line = null; 
       while((line=bufferedReader.readLine())!=null){ 
        stringBuilder.append(line+"\n"); 
       } 
       result = stringBuilder.toString(); 

      }catch (ClientProtocolException e){ 
       e.printStackTrace(); 
      }catch (UnsupportedEncodingException e){ 
       e.printStackTrace(); 
      }catch (IOException e){ 
       e.printStackTrace(); 
      } 

      return result; 
     } 
    } 

Answer 1

尝试调用AsyncTask前检查网络连接，是这样的：

private boolean isNetworkAvailable() { 
ConnectivityManager connectivityManager = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE); 
NetworkInfo activeNetworkInfo = connectivityManager.getActiveNetworkInfo(); 
return activeNetworkInfo != null && activeNetworkInfo.isConnected(); 
} 

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你可以找到文档here。