使用Volley以一种方法发出两个独立的远程请求

您应该使用回调(接口),而不是使用返回值。

• 返回值与同步任务一起工作,例如在不需要将计算代码放入单独的线程时计算两个数字的和。
• 返回值不适用于异步任务,如调用RESTAPI或执行耗时较长的任务。因为它的名字 异步的 说它将并行执行任务。

您的代码将做什么(完全错误):

• 它将创建一个列表

• 将在单独的任务中调用API( See AsyncTask ,所以您的代码不会等待它的响应。

• 它将返回空白列表。

• 现在,当你的反应出现时,这与此无关。

解决方案:

如果你知道接口,你就应该使用它。接口用于在任务完成时调用某些方法。

在代码中实现API的正确方法如下

    public static final int REQUEST_CODE_POPULAR = 1;
    public static final int REQUEST_CODE_TOP_RATED = 2;

    ArrayList<Movie> popularMoviesList = new ArrayList<>();
    ArrayList<Movie> topRatedMoviesList = new ArrayList<>();

    private void setData() {
        String popularMoviesUrl = "yourUrl";
        String topRatedMovieUrl = "yourUrl";
        MovieDataSource object = new MovieDataSource(); // use only one object
        OnResponseListener<ArrayList<Movie>> listener = new OnResponseListener<ArrayList<Movie>>() {
            @Override
            public void onSuccess(int tag, ArrayList<Movie> object) {
                if (tag == REQUEST_CODE_POPULAR) {
                    popularMoviesList = object;
                    // TODO: 5/27/2018 use this list further
                } else if (tag == REQUEST_CODE_TOP_RATED) {
                    topRatedMoviesList = object;
                    // TODO: 5/27/2018 use this list further
                }
            }

            @Override
            public void onError(Exception e) {
//            todo handle error
            }
        };
        object.movieArrayList(popularMoviesUrl, REQUEST_CODE_POPULAR, listener);
        object.movieArrayList(topRatedMovieUrl, REQUEST_CODE_TOP_RATED, listener);
    }

还有你的 MovieDataSource 班级。

import android.graphics.Movie;
import android.util.Log;

import com.android.volley.Request;
import com.android.volley.RequestQueue;
import com.android.volley.Response;
import com.android.volley.VolleyError;
import com.android.volley.toolbox.JsonObjectRequest;

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import java.util.ArrayList;
import java.util.List;

public class MovieDataSource {
    private final static String MOVIE_ID = "id";
    private final static String MOVIE_RATING = "vote_average";
    private final static String MOVIE_TITLE = "original_title";
    private final static String MOVIE_POSTERPATH = "poster_path";
    private final static String MOVIE_DESCRIPTION = "overview";
    private final static String MOVIE_RELEASEDATE = "release_date";
    private final static String API_KEY = "";// paste api key inside the double quote
    private RequestQueue mRequestQueue = VolleySingleton.getmInstance().getmRequestQueue();

    public void movieArrayList(String URL, final int tag, final OnResponseListener<ArrayList<Movie>> listener) {
        final ArrayList<Movie> listOfMovies = new ArrayList<>();
        String url = URL + API_KEY;
        JsonObjectRequest jsonObjectRequest = new JsonObjectRequest
                (Request.Method.GET, url, null, new Response.Listener<JSONObject>() {
                    @Override
                    public void onResponse(JSONObject response) {
                        int movieId;
                        double movieRating;
                        String movieTitle, imagePath, movieDescription, movieReleaseDate;
                        try {
                            JSONArray results = response.getJSONArray("results"); // get json array from the object
                            JSONObject object; // to get objects from result array
                            Movie movie;
                            for (int i = 0; i < results.length(); i++) {
                                object = results.getJSONObject(i);// get objects in the array based on their position/index in the array
                                //get values from the objects that will be used to populate instantiated movies
                                movieId = object.getInt(MOVIE_ID);
                                movieRating = object.getDouble(MOVIE_RATING);
                                movieTitle = object.optString(MOVIE_TITLE);
                                imagePath = object.optString(MOVIE_POSTERPATH);
                                movieDescription = object.optString(MOVIE_DESCRIPTION);
                                movieReleaseDate = object.optString(MOVIE_RELEASEDATE);
                                //// for every element in the array( index i), create a new movie
                                movie = new Movie(movieId, movieRating, movieTitle, imagePath, movieDescription, movieReleaseDate);
                                // add each movie created to the arrayList
                                listOfMovies.add(movie);
                            }
                        } catch (JSONException e) {
                            e.printStackTrace();
                        }
                        listener.onSuccess(tag, listOfMovies);
                    }
                }, new Response.ErrorListener() {
                    @Override
                    public void onErrorResponse(VolleyError error) {
                        listener.onError(error);
                        error.printStackTrace();
                        Log.i("error", "onErrorResponse: something went wrong ");
                    }
                });

        mRequestQueue.add(jsonObjectRequest);
      // removed return type, as it was redundant. 
    }


    interface OnResponseListener<T extends List> {
        void onSuccess(int tag, T object);
        void onError(Exception e);
    }
}

这是因为您的请求是异步运行的。所以,使用相同的moviedatasource运行2个请求。当两个请求都完成时,您将填充相同的moviedatasource.listofmovies,然后返回。尝试为mainActivity中的每个请求创建单独的moviedatasource。

MovieDataSource movieDataSource1 = new MovieDataSource();
final ArrayList<Movie>popularMoviesList = movieDataSource1.movieArrayList(popularMoviesUrl)
MovieDataSource movieDataSource2 = new MovieDataSource();
final ArrayList<Movie> topRatedMoviesList = movieDataSource2.movieArrayList(topRatedMovieUrl);

但老实说,这条规则对我来说是错误的。您立即返回空数组,然后在请求完成时填充它,但是您的MainActivity应该如何知道它是否就绪?我将传递来自MainActivity的完成回调,当请求完成时,可以使用接收的数组作为参数调用它。问我你是否需要其他帮助。