Android：AsyncTask 未达到 onPostExecute

Question

我正在使用 AsyncTask 来避免我的 Android 库项目出现 networkonmainthreadexception，现在我想做的是将要 return 的值赋给我的变量并在执行之前等待它下一行代码。我用 CountDownLatch 来做这个。

我执行请求和调用 AsyncTask 的方式写在下面。所以我使用 CountDownLatch 来等待响应，然后 returning 我想要 return 的值。

public MyObject getMyObject(){

    final String url = "http://[myip]:8080/retrieve";

    try{
        Response response = executeRequest(url);
        final MyObject myObject = om.readValue(response.body().string(),
                new TypeReference<MyObject>() {
                });
        return myObject;
    } catch (Exception e) {
        e.printStackTrace();
    }

    return null;

}



private Response executeRequest(String url){

    try {
      //Simplified please just ignore this..
      GenericAsyncParams genericAsyncParams = createParams(......);

      final CountDownLatch countDownLatch = new CountDownLatch(1);
      ResponseListener responseListener = new ResponseListener(countDownLatch);
      MyAsyncTask myAsyncTask = new AsyncTask(responseListener);
      myAsyncTask.execute(genericAsyncParams);
      countDownLatch.await();

      //get the response from the listener class.
      Response response = responseListener.getResponse();
      return response;
    } catch (InterruptedException e) {
      e.printStackTrace();
    }

    return null;
  }

我也知道 asyncTask.execute(args).get() 可能会导致异常，所以我使用了一个监听器来更新调用者的值，我在我的 AsyncTask 的 onPostExecute 上调用 setResponse。

public class ResponseListener {

    private static final String TAG = ResponseListener.class.getName();

    private Response response;
    private CountDownLatch countDownLatch;

    public ResponseListener(CountDownLatch countDownLatch) {
        this.response = null;
        this.countDownLatch = countDownLatch;
    }

    public void setResponse(Response response){
        this.response = response;   
        Log.e(TAG, "Executing countdown..");
        countDownLatch.countDown();
    }

    public Response getResponse() {
        return response;
    }

    public CountDownLatch getCountDownLatch() {
        return countDownLatch;
    }
}

现在这是我的 AsyncTask 注意：requestProcessor 是 okHttp 的包装器 class。

public class MyAsynctask extends AsyncTask<GenericAsyncParams, Void, Response>{


    private static final String TAG = MyAsyncTask.class.getName();

    private ResponseListener listener;

    public MyAsynctask(ResponseListener listener) {
        this.listener = listener;
    }

    @Override
    protected Response doInBackground(GenericAsyncParams... genericAsyncParamses) {
        Response response = null;
        GenericAsyncParams genericAsyncParams = genericAsyncParamses[0];
        String url = genericAsyncParams.getUrl();
        String method = genericAsyncParams.getMethod();
        RequestProcessor requestProcessor = genericAsyncParams.getRequestProcessor();

        try {
            Request.Builder builder;
            if(method.equalsIgnoreCase("POST")){
                builder = new Request.Builder()
                        .post(genericAsyncParams.getRequestBody())
                        .url(url)
                        .headers(headers);
            } else  {
                builder = new Request.Builder()
                        .headers(headers)
                        .get()
                        .url(url);
            }
            final Request request = builder.build();
            response = requestProcessor.client().newCall(request).execute();
            Log.d(TAG, "returning okHttp response..");
            return response;
        } catch (Exception e){
            Log.e(TAG, String.format("ERROR.. %s", ExceptionUtils.getMessage(e)));
        }

        return response;
    }


    @Override
    protected void onPostExecute(Response response) {
        if(listener != null){
            Log.d(TAG, "Updating response : onPostExecute..");
            listener.setResponse(response);
        } else {
            super.onPostExecute(response);
        }
    }

}

我日志的最后一行是

07-10 23: 47:07.008 28409-28530/com.aaron.android.android.lib D/com.aaron.android.android.lib.api.tasks.MyAsyncTask: returning okHttp response..

Answer 1

NetworkOnMainException 提醒我们不要阻塞主线程 UI。但是，您仍然通过使用 CountDownLatch 等待响应来阻止它。由于 onPostExecute() 在主线程上运行，因此您已阻止它执行。在等待网络连接完成时，您不能阻塞主线程。相反，允许 executeRequest() 到 return 以便 UI 可以适当地响应。

Android：AsyncTask 未达到 onPostExecute

Android : AsyncTask not reaching onPostExecute

android

android-asynctask

countdownlatch