Android：AsyncTask 中的 NetworkOnMainThreadException 错误

Question

好的，所以我创建了一个扩展 AsycTask 的内部类，以便我的代码在 UI 线程中运行。但是我收到了这个错误，所以我认为这意味着我的 onPostExecute 的某些部分需要在 doInBackground 中完成，但是我无法弄清楚这是什么

public class asyncTask extends AsyncTask<String, Integer, String> {

        ProgressDialog dialog = new ProgressDialog(PetrolPriceActivity.this);

        @Override
           protected void onPreExecute() {
          dialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
          dialog.setProgress(0);
          dialog.setMax(100);
          dialog.setMessage("loading...");
          dialog.show();
           }

         @Override
           protected String doInBackground(String...parmans){
                {

                    for(int i = 0; i < 100; i++){


                        publishProgress(1);
                        try {
                            Thread.sleep(100);
                        } catch (InterruptedException e) {
                            // TODO Auto-generated catch block
                            e.printStackTrace();
                        }

                    }


                    String urlString = petrolPriceURL;
                    String result = "";
                    InputStream anInStream = null;
                    int response = -1;
                    URL url = null;

                    try {
                        url = new URL(urlString);
                    } catch (MalformedURLException e) {
                        // TODO Auto-generated catch block
                        return null;
                    }
                    URLConnection conn = null;
                    try {
                        conn = url.openConnection();
                    } catch (IOException e) {
                        // TODO Auto-generated catch block
                        return null;
                    }

                    // Check that the connection can be opened
                    if (!(conn instanceof HttpURLConnection))
                        try {
                            throw new IOException("Not an HTTP connection");
                        } catch (IOException e) {
                            // TODO Auto-generated catch block
                            return null;
                        }
                    try
                    {
                        // Open connection
                        HttpURLConnection httpConn = (HttpURLConnection) conn;
                        httpConn.setAllowUserInteraction(false);
                        httpConn.setInstanceFollowRedirects(true);
                        httpConn.setRequestMethod("GET");
                        httpConn.connect();
                        response = httpConn.getResponseCode();
                        // Check that connection is OK
                        if (response == HttpURLConnection.HTTP_OK)
                        {
                            // Connection is OK so open a reader 
                            anInStream = httpConn.getInputStream();
                            InputStreamReader in= new InputStreamReader(anInStream);
                            BufferedReader bin= new BufferedReader(in);

                            // Read in the data from the RSS stream
                            String line = new String();
                            while (( (line = bin.readLine())) != null)
                            {
                                result = result + "\n" + line;
                            }
                        }
                    }
                    catch (IOException ex)
                    {
                            try {
                                throw new IOException("Error connecting");
                            } catch (IOException e) {
                                // TODO Auto-generated catch block
                                e.printStackTrace();
                            }
                    }

            return result;

                }
           }
           @Override

           protected void onProgressUpdate(Integer...progress){

               dialog.incrementProgressBy(progress[0]);
           }

           @Override
           protected void onPostExecute(String result) {
               // Get the data from the RSS stream as a string

               errorText = (TextView)findViewById(R.id.error);
               response = (TextView)findViewById(R.id.title);

               try
                {
                    // Get the data from the RSS stream as a string
                    result =  doInBackground(petrolPriceURL);
                    response.setText(result);
                    Log.v(TAG, "index=" + result);
                }
                catch(Exception ae)
                {
                    // Handle error
                    errorText.setText("Error");
                    // Add error info to log for diagnostics
                    errorText.setText(ae.toString());
                } 
                if(dialog.getProgress() == dialog.getMax())
                dialog.dismiss();

           }
        }

如果有人能指出我的错误，并举例说明代码在我的 doInBackground 中的位置，那就太好了。谢谢

Answer 1

问题：

result =  doInBackground(petrolPriceURL);

您在onPostExecute 中隐式调用doInbackground 方法，该方法实际上将在您的UI 线程中运行，而不是在不同的线程上，从而导致Android:NetworkOnMainThreadException。

当你执行你的Asynctask时，也没有必要调用doInBackground，它已经在onPostExecute之前执行了。直接使用onPostExecute的result参数即可。

样本：

@Override
       protected void onPostExecute(String result) {
           // Get the data from the RSS stream as a string

           errorText = (TextView)findViewById(R.id.error);
           response = (TextView)findViewById(R.id.title);

            response.setText(result);

            if(dialog.getProgress() == dialog.getMax())
            dialog.dismiss();

       }

Answer 2

我怀疑错误与您的这部分代码有关：

try
 {
 // Get the data from the RSS stream as a string
 result =  doInBackground(petrolPriceURL);
 response.setText(result);
 Log.v(TAG, "index=" + result);
 }

doInBackgound 会在您调用 asynctask.execute 时自动调用。要正确启动任务，您应该 (1) 创建任务的新实例； （2）在execute方法中传递doInBackground中需要使用的字符串参数； (3) 使用它们； (4)将结果返回给onPostExecute。

例如：

 //in your activity or fragment
 MyTask postTask = new MyTask();
 postTask.execute(value1, value2, value3);

 //in your async task
 @Override
 protected String doInBackground(String... params){

      //extract values
      String value1 = params[0];
      String value2 = params[1];
      String value3 = params[2];

      // do some work and return result
      return value1 + value2;
 }

 @Override
 protected void onPostExecute(String result){

      //use the result you returned from you doInBackground method
 }

您应该尝试在 doInBackground 方法中完成所有“工作”。 Reutrn 您要在主/UI 线程上使用的结果。这将自动作为参数传递给 onPostExecute 方法（在主/UI 线程上运行）。