当AsyncTask未完成时不能关闭Activity

Question

我有一个AsyncTask运行在我的Activity。在AsyncTask的doInBackground(Object[])方法中，我执行一个网络操作，使用HTTP POST方法向服务器发送一些数据，接收响应，然后在onPostExecute(Object)方法中将该响应发送给Service，然后从Service执行所有工作。问题是:我不能关闭Activity，直到AsyncTask完成。Activity只是冻结，直到AsyncTask完成。有时，如果AsyncTask需要更多的时间来完成，屏幕就会变黑，直到AsyncTask完成。为什么呢?如何避免这种情况?我尝试在Activity的onStop()方法中调用AsyncTask的cancel(boolean)，但它仍然执行相同的行为。

编辑:my AsyncTask code:

private static class PostCommentTask extends AsyncTask<String, Void, String> {
    Activity activity;
    int status;
    Toast indicationMsg;
    public PostCommentTask(Context context) {
        activity = (Activity) context;
    }
    private boolean isNetworkAvailable() {
        Log.i("ilog", "isNetworkAvailable() called");
        ConnectivityManager connManager = (ConnectivityManager) activity.getSystemService(Context.CONNECTIVITY_SERVICE);
        NetworkInfo activeNetworkInfo = connManager.getActiveNetworkInfo();
        return activeNetworkInfo != null && activeNetworkInfo.isConnected() && activeNetworkInfo.isAvailable();
    }
    protected String doInBackground(String... param) {
        if (!isNetworkAvailable()) {
            return "";
        }
        HttpClient httpClient = new DefaultHttpClient();
        HttpPost httpPost = new HttpPost(param[7]);
        String responseBody = "error in PostComment.doInBackground()";
        try {
            List<NameValuePair> params = new ArrayList<NameValuePair>(7);
            params.add(new BasicNameValuePair("somevar", param[0]));
            params.add(new BasicNameValuePair("somevar", param[1]));
            params.add(new BasicNameValuePair("somevar", param[2]));
            params.add(new BasicNameValuePair("somevar", param[3]));
            params.add(new BasicNameValuePair("somevar", param[4]));
            params.add(new BasicNameValuePair("somevar", param[5]));
            params.add(new BasicNameValuePair("somevar", param[6]));
            httpPost.setEntity(new UrlEncodedFormEntity(params));
            HttpResponse response = httpClient.execute(httpPost);
            status = response.getStatusLine().getStatusCode();
            Log.i("ilog", "response status: " + status);
            HttpEntity responseEntity = response.getEntity();
            if (responseEntity != null) {
                responseBody = EntityUtils.toString(responseEntity);
            }
        } catch (ClientProtocolException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
        Log.i("ilog", "Response: " + responseBody);
        return responseBody;
    }
    public void onPostExecute(String responseBody) {
        String success = "{"status":"OK"}";
        if (responseBody.equals(success) && status == 200){
            indicationMsg = Toast.makeText(activity, "Success!!!", Toast.LENGTH_LONG);
            CommentsFragment.CommentsHandler commentsHandler = new CommentsFragment.CommentsHandler();
            Messenger messenger = new Messenger(commentsHandler);
            Intent serviceIntent = new Intent(activity, WindowService.class);
            serviceIntent.putExtra("messenger", messenger);
            serviceIntent.putExtra("somevar", somevar);
            serviceIntent.putExtra("somevar", activity.getIntent().getStringExtra("somevar"));
            activity.startService(serviceIntent);
            //
        }
        else
            indicationMsg = Toast.makeText(activity, "Failed...", Toast.LENGTH_LONG);
        indicationMsg.show();
    }
}

CommentsHandler类是处理来自Service的响应的类。这就是我如何在Activity和Service之间进行通信的。

我用下面的代码开始AsyncTask:

public static class CommentsFragment extends Fragment {
    /** ... **/
    @Override
    public void onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        /** ... **/
        Button queryButton = (Button) rootView.findViewById(R.id.query_button);
        queryButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                /** ... **/
                new PostCommentTask(activity).execute(somevar, somevar, somevar, somevar, somevar, somevar, somevar, somevar);
                /** ... **/
            }
        });
        /** ...  **/
    }
    /** ... **/
}

Answer 1

我已经修复了这个问题。Activity正在冻结，因为我从这个返回的Activity也在其onResume()方法中使用AsyncTask，所以它必须等到关闭的Activity的第一个任务完成后才执行自己的任务，这导致了UI的冻结。现在我使用executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR, Object[]能够并行运行多个任务，而不是串联(一个接一个)。