从Android的doInBackground（）获得响应之前调用AsyncTask onPostExecute（）吗？

Question

Here is my code:-

Goals.java class

public class Goals  extends AppCompatActivity{

    private ArrayList<Goal> result;
    private RecyclerView.Adapter adapter;
    private RecyclerView recyclerView;
    private RecyclerView.LayoutManager layoutManager;
    private ArrayList<Goal> dataFromServer;
    private Toolbar toolbar;


    //This is for back button
    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
            case android.R.id.home:
                startActivity(new Intent(this, MainActivity.class));
                finish();
                return true;
        }
        return super.onOptionsItemSelected(item);
    }


    @Override
    protected void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.goal_list);

        recyclerView=(RecyclerView) findViewById(R.id.goal_recycler_view);
        toolbar=(Toolbar) findViewById(R.id.toolbar);


        recyclerView.setHasFixedSize(true);

        layoutManager=new LinearLayoutManager(this);
        recyclerView.setLayoutManager(layoutManager);

        setSupportActionBar(toolbar);

        //FOr back button
        getSupportActionBar().setDisplayHomeAsUpEnabled(true);
        getSupportActionBar().setDisplayShowHomeEnabled(true);
        getSupportActionBar().setDisplayShowTitleEnabled(false);


        //fetch goal list from server and also its related action
        getData();

        //Send Data to GoalAdaptor
        showData();

    }

    private void showData() {
        Log.i("Show Date","Enter");
        System.out.println("Result Array List"+result.toString());
        adapter=new goalAdaptor(this, result);
        recyclerView.setAdapter(adapter);
    }

    private void getData() {

        result=new ArrayList<>();

        DownloadPlansFromServer server= new DownloadPlansFromServer();
        server.execute();

    }


    class DownloadPlansFromServer extends AsyncTask<Void,Void,Boolean>
    {

        private ProgressDialog progressDialog;
        Boolean planActive=false;

        protected void onPreExecute() {
            // NOTE: You can call UI Element here.

            //UI Element
            progressDialog = new ProgressDialog(Goals.this);

            progressDialog.setMessage("Downloading Plans Data..");
            progressDialog.show();
        }


        @Override
        protected Boolean doInBackground(Void... params) {



            try {

                Response.Listener listener=new Response.Listener<JSONObject>()
                {
                    @Override
                    public void onResponse(JSONObject response) {
                        try {

                            System.out.println("Inside the response");
                            // Parsing json object response
                            // response will be a json object

                            System.out.println("Output is "+response.toString());


                            //Toast.makeText(getApplicationContext(),response.toString(),Toast.LENGTH_LONG).show();

                            planActive=response.getBoolean("success");



                            if (planActive)
                            {
                                JSONArray plansArray=response.getJSONArray("response");

                                //get Plans Details
                                for (int p=0;p<plansArray.length();p++)
                                {
                                    JSONObject plan=plansArray.getJSONObject(p);

                                    //get Goals Details
                                    JSONObject planGoals=plan.getJSONObject("goal");

                                    Goal goal=new Goal();
                                    goal.setGoal_name("Goal Name:- "+planGoals.getString("goal_name"));

                                    Log.i("Goal Name is",planGoals.getString("goal_name"));

                                    JSONObject currentValue=planGoals.getJSONObject("current_value");
                                    JSONObject targetValue=planGoals.getJSONObject("target_value");

                                    //Get the values parameter
                                    ArrayList<String> parameterList=getTheParameter(planGoals.getString("goal_id"));

                                    if (parameterList.isEmpty())
                                    {
                                        System.out.println("Problem WHile Processing the parameter ");
                                    }
                                    else
                                    {
                                        String goalDescription="Reduce the value from";

                                        StringBuilder currentStringBuilder=new StringBuilder();

                                        for (int k=0;k<parameterList.size();k++)
                                        {
                                            currentStringBuilder.append(currentValue.getString(parameterList.get(k))+"/");
                                        }

                                        StringBuilder targetStringBuilder=new StringBuilder();

                                        for (int k=0;k<parameterList.size();k++)
                                        {
                                            targetStringBuilder.append(targetValue.getString(parameterList.get(k))+"/");

                                        }

                                        goal.setGoal_description(goalDescription+currentStringBuilder.toString()+" to "+ targetStringBuilder.toString());
                                    }

                                    //Add the result to the array
                                    result.add(goal);

                                }

                            }


                        }
                        catch (JSONException k)
                        {
                            Log.i("On Response",k.getMessage());
                            k.printStackTrace();
                        }

                    }
                };


                Response.ErrorListener errorListener=new Response.ErrorListener() {
                    @Override
                    public void onErrorResponse(VolleyError error) {

                        //   Handle Error
                        if (error instanceof TimeoutError || error instanceof NoConnectionError) {
                            error.printStackTrace();
                            Toast.makeText(getApplicationContext(), " this Network Error", Toast.LENGTH_SHORT).show();
                        } else if (error instanceof AuthFailureError) {
                            //TODO
                            error.printStackTrace();
                            Toast.makeText(getApplicationContext(), "User not authorized", Toast.LENGTH_SHORT).show();
                        } else if (error instanceof ServerError) {
                            //TODO
                            error.printStackTrace();
                            Toast.makeText(getApplicationContext(), "Server error", Toast.LENGTH_SHORT).show();
                        } else if (error instanceof NetworkError) {
                            //TODO
                            error.printStackTrace();
                            Toast.makeText(getApplicationContext(), "Network Error", Toast.LENGTH_SHORT).show();
                        } else if (error instanceof ParseError) {
                            //TODO
                            error.printStackTrace();
                            Toast.makeText(getApplicationContext(), "Error consuming request", Toast.LENGTH_SHORT).show();
                        }
                        else error.printStackTrace();
                    }
                };

                String plan_url=Constants.url+"plan";

                JsonObjectHeader customRequest=new JsonObjectHeader(plan_url,null, listener, errorListener);
                RequestQueue requestQueue = Volley.newRequestQueue(getApplicationContext());
                requestQueue.add(customRequest);

                System.out.println("After custom Request");

                planActive=true;

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


            return planActive;
        }


        protected void onPostExecute(Boolean unused) {
            // NOTE: You can call UI Element here.

            // Close progress dialog
            progressDialog.dismiss();

            if (unused)
            {
                Log.i("Get Plan","Yes");
                //showData();

            }

            else
                Toast.makeText(getApplicationContext(),"No Plans Found",Toast.LENGTH_LONG).show();

        }


    }

    private ArrayList<String> getTheParameter(String goal_id) {

        ArrayList<String> arrayList=new ArrayList<>();

        if (goal_id.equals("bp"))
        {
            arrayList.add("systolic");
            arrayList.add("diastolic");

            return arrayList;
        }
        else
        {
            arrayList.add(null);
            return arrayList;
        }



    }


}

The problem is:- Before getting the response from server, the onPostExecute() function executed. So I will get empty result arraylist.

JsonObjectHeader class is the basic volley class to fetch data from server.

Answer 1

No need to use async task while you want network call by using any third party library. because the volly create its own thread for network call.

Answer 2

If you are using volley library then remove AsyncTask and write this code in simple method

 try {

            Response.Listener listener=new Response.Listener<JSONObject>()
            {
                @Override
                public void onResponse(JSONObject response) {
                    try {

                        System.out.println("Inside the response");
                        // Parsing json object response
                        // response will be a json object

                        System.out.println("Output is "+response.toString());


                        //Toast.makeText(getApplicationContext(),response.toString(),Toast.LENGTH_LONG).show();

                        planActive=response.getBoolean("success");



                        if (planActive)
                        {
                            JSONArray plansArray=response.getJSONArray("response");

                            //get Plans Details
                            for (int p=0;p<plansArray.length();p++)
                            {
                                JSONObject plan=plansArray.getJSONObject(p);

                                //get Goals Details
                                JSONObject planGoals=plan.getJSONObject("goal");

                                Goal goal=new Goal();
                                goal.setGoal_name("Goal Name:- "+planGoals.getString("goal_name"));

                                Log.i("Goal Name is",planGoals.getString("goal_name"));

                                JSONObject currentValue=planGoals.getJSONObject("current_value");
                                JSONObject targetValue=planGoals.getJSONObject("target_value");

                                //Get the values parameter
                                ArrayList<String> parameterList=getTheParameter(planGoals.getString("goal_id"));

                                if (parameterList.isEmpty())
                                {
                                    System.out.println("Problem WHile Processing the parameter ");
                                }
                                else
                                {
                                    String goalDescription="Reduce the value from";

                                    StringBuilder currentStringBuilder=new StringBuilder();

                                    for (int k=0;k<parameterList.size();k++)
                                    {
                                        currentStringBuilder.append(currentValue.getString(parameterList.get(k))+"/");
                                    }

                                    StringBuilder targetStringBuilder=new StringBuilder();

                                    for (int k=0;k<parameterList.size();k++)
                                    {
                                        targetStringBuilder.append(targetValue.getString(parameterList.get(k))+"/");

                                    }

                                    goal.setGoal_description(goalDescription+currentStringBuilder.toString()+" to "+ targetStringBuilder.toString());
                                }

                                //Add the result to the array
                                result.add(goal);

                            }

                        }


                    }
                    catch (JSONException k)
                    {
                        Log.i("On Response",k.getMessage());
                        k.printStackTrace();
                    }

                }
            };


            Response.ErrorListener errorListener=new Response.ErrorListener() {
                @Override
                public void onErrorResponse(VolleyError error) {

                    //   Handle Error
                    if (error instanceof TimeoutError || error instanceof NoConnectionError) {
                        error.printStackTrace();
                        Toast.makeText(getApplicationContext(), " this Network Error", Toast.LENGTH_SHORT).show();
                    } else if (error instanceof AuthFailureError) {
                        //TODO
                        error.printStackTrace();
                        Toast.makeText(getApplicationContext(), "User not authorized", Toast.LENGTH_SHORT).show();
                    } else if (error instanceof ServerError) {
                        //TODO
                        error.printStackTrace();
                        Toast.makeText(getApplicationContext(), "Server error", Toast.LENGTH_SHORT).show();
                    } else if (error instanceof NetworkError) {
                        //TODO
                        error.printStackTrace();
                        Toast.makeText(getApplicationContext(), "Network Error", Toast.LENGTH_SHORT).show();
                    } else if (error instanceof ParseError) {
                        //TODO
                        error.printStackTrace();
                        Toast.makeText(getApplicationContext(), "Error consuming request", Toast.LENGTH_SHORT).show();
                    }
                    else error.printStackTrace();
                }
            };

            String plan_url=Constants.url+"plan";

            JsonObjectHeader customRequest=new JsonObjectHeader(plan_url,null, listener, errorListener);
            RequestQueue requestQueue = Volley.newRequestQueue(getApplicationContext());
            requestQueue.add(customRequest);

because in volley you can get response in onResponse so add onPostExecute inside this

Answer 3

Your issue is that you are creating an additional thread in your onBackground(Void...) .

Your code sees:

1. Start onPreExecute.
2. Show Dialog.
3. Return from onPreExecute.
4. Start onBackground.
5. New thread created by Volley Request (Thread #2)
6. Return from onBackground.
7. Start onPostExecute.
8. Close Dialog.
9. Return from onPostExecute.
10. Return from Thread #2.

You need to use a blocking method from the Volley system. This answer explains it.

RequestFuture<JSONObject> future = RequestFuture.newFuture();
JsonObjectRequest request = new JsonObjectRequest(Method.POST, SIGNUP_URL, reqBody, future, future)
volleyRequestQueue.add(request);

try {
    JSONObject response = future.get();
} catch (InterruptedException e) {
} catch (ExecutionException e) {
}

Answer 4

It's not your postExecute it's your

showData();

is executed before

getData();

is complete. Ideally move your showData code to your postExecute and you will get your results as expected.

Answer 5

Remove the AsyncTask.

Move all code from doInBackgroud in a normal function.

Call showSata() in onResponse().

Answer 6

I think you should read articles where is a good explanation why you should not have to use AsyncTask. My suggestion is start using Retrofit (for working with Http) + You do not have to parse JSON on your own, you can use @SerializedName annotation in your Response object

Here's a tutorial demonstrates how to fetch data from server and fill recycle view

Here is my code for signing in

Call<LoginResponse> call = retrofit.create(ComeAroundAPIInterface.class).signin(data);
    call.enqueue(new Callback<LoginResponse>() {
        @Override
        public void onResponse(Call<LoginResponse> call, Response<LoginResponse> response) {
            if (response.isSuccessful()) {               
                onLoginSuccess();
                sharedPreferences = getSharedPreferences(LOGIN_COOKIE, Context.MODE_PRIVATE);
                SharedPreferences.Editor editor = sharedPreferences.edit();
                editor.putBoolean("LOGIN",true);
                editor.commit();
                progressDialog.dismiss();
                Intent intent = new Intent(LoginActivity.this, MainActivity.class);
                intent.putExtra("user", (LoginResponse)response.body());
                startActivity(intent);
                finish();
            } else {
                progressDialog.cancel();
                onLoginFailed();
                Converter<ResponseBody, APIError> converter = retrofit.responseBodyConverter(APIError.class, new Annotation[0]);
                APIError error = new APIError();
                try {error = converter.convert(response.errorBody());} catch (IOException e) {}
                Toast.makeText(getBaseContext(),error.message(),Toast.LENGTH_SHORT).show();
            }
        }
        @Override
        public void onFailure(Call<LoginResponse> call, Throwable t) {
            onLoginFailed();
            Log.e("Login", t.toString());
        }
    });

and here is my Response class with @SerializedName annotation

public class LoginResponse implements Parcelable{
    @SerializedName("id")
    private String id;
    @SerializedName("username")
    private String username;
    @SerializedName("email")
    private String email;
    @SerializedName("name")
    private String name;
    @SerializedName("sirname")
    private String sirname;

    //getters