java - 在 android 中从 doInBackground() 获取响应之前调用 AsyncTask onPostExecute() 吗？

Question

这是我的代码:-

Goals.java 类

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;
        }



    }


}

问题是:- 在从服务器获取响应之前，执行了 onPostExecute() 函数。所以我会得到空结果数组列表。

JsonObjectHeader 类是从服务器获取数据的基本 volley 类。

Answer 1

当您需要使用任何第三方库进行网络调用时，无需使用异步任务。因为volly创建了自己的线程用于网络调用。