Android - AsyncTask 未执行

Question

我知道这个标题已经有很多问题，但我仍然没有找到适合我的案例的解决方案。

我有以下代码从在线数据库中获取用户数据。如标题所述，问题是 AsyncTask 没有启动。

这是我的代码:

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    getData(); // retrieves "friends" data from database
    FloatingActionButton btn3 = (FloatingActionButton) findViewById(R.id.button_add_new_friend);
    btn3.setBackgroundTintList(getResources().getColorStateList(R.color.Blonde));
    btn3.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {

            LayoutInflater layoutInflater = LayoutInflater.from(profile.this);
            View promptView = layoutInflater.inflate(R.layout.input_new_friend, null);
            AlertDialog.Builder alertDialogBuilder = new AlertDialog.Builder(profile.this);
            alertDialogBuilder.setView(promptView);

            final EditText editText1 = (EditText) promptView.findViewById(R.id.edittext_addnewfriend);

            // setup a dialog window
            alertDialogBuilder.setCancelable(false)
                .setPositiveButton("OK", new DialogInterface.OnClickListener() {
                    public void onClick(DialogInterface dialog, int id) {

                        StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
                        StrictMode.setThreadPolicy(policy);

                        InputStream is = null;

                        // add values to the database
                        String friend = "" + editText1.getText();

                        // Verify the user in the USERS database - get users data from the dabase
                        GetDataJSON g = new GetDataJSON();
                        g.execute();                                
                        if (friends.contains(friend)) // if you are already friends with that user
                            Toast.makeText(getApplicationContext(), "You are already friends with that user!",
                                Toast.LENGTH_LONG).show();
                        else {
                            if (!users.contains(friend)) // the user doesn't exist in our database
                                Toast.makeText(getApplicationContext(), "That user doesn't exist! You either haven't introduced the right email or he's not a registered user within Poinder.",
                                    Toast.LENGTH_LONG).show();
                        else // the user exists so we add him to the friends list
                        {
                            //do something
                        }
}

// Getting the users
protected void showList2(){
    try {
        JSONObject jsonObj = new JSONObject(myJSON);
        people = jsonObj.getJSONArray(TAG_RESULTS);

        for(int i=0;i<people.length();i++){
            JSONObject c = people.getJSONObject(i);
            String user = c.getString(TAG_USER);
            String email = c.getString(TAG_EMAIL);
            Double location_latitude = c.getDouble(TAG_LATITUDE);
            Double location_longitude = c.getDouble(TAG_LONGITUDE);

            users.add(email);
        }

    } catch (JSONException e) {
        e.printStackTrace();
    }

}

// Getting the users
private class GetDataJSON extends AsyncTask<Void, Void, String> {

    @Override
    protected String doInBackground(Void... params) {
        DefaultHttpClient httpclient = new DefaultHttpClient(new BasicHttpParams());
        HttpPost httppost = new HttpPost("http://xxxxxxx/friends_out.php");

        // Depends on your web service
        httppost.setHeader("Content-type", "application/json");

        InputStream inputStream = null;
        String result = null;
        try {
            HttpResponse response = httpclient.execute(httppost);
            HttpEntity entity = response.getEntity();

            inputStream = entity.getContent();
            // json is UTF-8 by default
            BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream, "UTF-8"), 8);
            StringBuilder sb = new StringBuilder();

            String line = null;
            while ((line = reader.readLine()) != null)
            {
                sb.append(line + "\n");
            }
            result = sb.toString();
        } catch (Exception e) {
            // Oops
        }
        finally {
            try{if(inputStream != null)inputStream.close();}catch(Exception squish){}
        }
        return result;
    }

    @Override
    protected void onPostExecute(String result){
        myJSON=result;
        showList2();
    }
}

知道我应该改用什么其他方法吗？或者最好我应该如何修改这个工作以及为什么我的 AsyncTask 永远不会启动？

编辑:我应用了下面提到的所有建议，不幸的是，到目前为止它们都不起作用(我的 AsyncTask 仍然没有启动)。

还有一个问题:在同一个 Activity 中使用多个 AsyncTask 与我的问题有关吗？

Answer 1

由于(我假设)其他建议的解决方案都不起作用，我怀疑您的问题在于 AsyncTask 的执行方式。如果多个 AsyncTask 在同一个 Activity 中执行，例如在您的应用程序中，那么这些 AsyncTask 将不会并行执行。他们将一个接一个地执行。

我怀疑您的其他 AsyncTask 正在长时间运行，因此您的 GetDataJSON AsyncTask 正在等待其他任务完成。

解决方案是启用 AsyncTask 的并行执行。使用以下代码并行执行 AsyncTasks。

GetDataJSON g = new GetDataJSON();
g.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR);

来自 AsyncTask 文档:

Order of execution

When first introduced, AsyncTasks were executed serially on a single background thread. Starting with DONUT, this was changed to a pool of threads allowing multiple tasks to operate in parallel. Starting with HONEYCOMB, tasks are executed on a single thread to avoid common application errors caused by parallel execution.

If you truly want parallel execution, you can invoke executeOnExecutor(java.util.concurrent.Executor, Object[]) with THREAD_POOL_EXECUTOR.

希望这会有所帮助。