如何在AsyncTask中实现自定义ArrayList？

Question

我正在构建一个采用API（电影数据库）并提取JSON数组的Android应用程序。 提取后，将适当的JSONObject发送到模型。 该模型是一个由setter和getter组成的类，用于提取对象并将其分配给我可以使用的变量。 所有这些都是在AsyncTask上完成的。 但是，我很难理解doInBackground方法，因为它希望我返回一些东西。 我已经完成了getMovieJson方法的所有工作，而且我知道我必须从doInBackground返回某些内容，因为需要更新onPostExecute方法上的自定义适配器。 此自定义适配器是ArrayAdapter，它创建适当的视图以填充到我的gridView中。

这是我的模特

package com.xxcanizeusxx.erick.moviesnow;

/**
 * This class acts as the model base for our
 * array of JSON Objects that need to be populated.\
 * This class uses getters and setters to achieve its task.
 */

public class Movie {

    private String title;
    private String vote_average;
    private String overview;
    private String release_date;
    private String poster_path;

    public String getTitle(){
        return title;
    }

    public void setTitle(String title){
        this.title = title;
    }

    public String getOverview(){
        return overview;
    }

    public void setOverview(String overview){
        this.overview = overview;
    }

    public String getRelease_date(){
        return release_date;
    }

    public void setRelease_date(String release_date){
        this.release_date = release_date;
    }

    public String getVote_average(){
        return vote_average;
    }

    public void setVote_average(String vote_average){
        this.vote_average = vote_average;
    }


    public String getPoster_path(){
        return poster_path;
    }

    public void setPoster_path(String poster_path){
        this.poster_path = poster_path;
    }


}

这是我的片段

package com.xxcanizeusxx.erick.moviesnow;

import android.net.Uri;
import android.os.AsyncTask;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.GridView;

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

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.ArrayList;

/**
 * Created by Erick on 1/4/2017.
 */

public class MovieFragment extends Fragment {
    //Initialize our array adapter and components.
    private ArrayList<Movie> mMovieData;
    private MovieAdapter mMovieAdapter;

    //Empty constructor
    public MovieFragment() {

    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        //Add this line in order for this fragment to handle menu events.
        setHasOptionsMenu(true);
    }

    @Override
    public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {
        inflater.inflate(R.menu.movie_fragment, menu);
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        int id = item.getItemId();
        if (id == R.id.popular_movies) {
            updateMovie();

            return true;
        }
        return super.onOptionsItemSelected(item);
    }

    private void updateMovie() {
        FetchMovieTask fetchMovie = new FetchMovieTask();
        fetchMovie.execute();
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        //Initialize our array adapter
        mMovieData = new ArrayList<>();
        mMovieAdapter = new MovieAdapter(getActivity(), R.layout.grid_movie_item, mMovieData);

        View rootView = inflater.inflate(R.layout.gird_layout, container, false);

        //Get a reference to the gridView and attach the adapter to it
        GridView mGridView = (GridView) rootView.findViewById(R.id.gridView);
        mGridView.setAdapter(mMovieAdapter);
        return rootView;
    }

    @Override
    public void onStart() {
        super.onStart();
        updateMovie();
    }

    public class FetchMovieTask extends AsyncTask<String[], Void, String[]> {
        private final String LOG = FetchMovieTask.class.getSimpleName();



        private  String[] getMovieJson(String movieJsonStr) throws JSONException {
            final String OWM_RESULTS = "results";
            String title;
            String posterPath;




            JSONObject movieJson = new JSONObject(movieJsonStr);
            JSONArray movieJsonArray = movieJson.getJSONArray(OWM_RESULTS);
            Movie movieItem = new Movie();
            //Newly created array  that will house the data in order to check for views on the onPostExecute method
            String[] results = new String[movieJsonStr.length()];
            for (int i = 0; i < movieJsonArray.length(); i++) {
                JSONObject movieObject = movieJsonArray.getJSONObject(i);
                title = movieObject.getString("title");
                posterPath = movieObject.getString("poster_path");
                movieItem.setTitle(title);
                movieItem.setPoster_path(posterPath);
                results[i] = movieObject.getString(posterPath) +" " + movieObject.getString(posterPath);


            }

            mMovieData.add(movieItem);
            return results;


        }


        @Override
        protected String[] doInBackground(String[]... params) {
            //Establish a connection
            HttpURLConnection urlConnection = null;
            BufferedReader bufferedReader = null;

            //Will contain the raw JSON as a string
            String movieJsonStr = null;
            //String as placeholders
            String descriptionHolder = "popularity.desc";

            try {
                //String to hold the Base url
                final String TMDB_BASE_URL = "http://api.themoviedb.org/3/discover/movie?";
                final String APPID = "api_key";
                final String DESC = "sort_by";

                //Build the url
                Uri buildMovieUri = Uri.parse(TMDB_BASE_URL).buildUpon()
                        .appendQueryParameter(DESC, descriptionHolder)
                        .appendQueryParameter(APPID, BuildConfig.TMDP_API_KEY)
                        .build();

                URL url = new URL(buildMovieUri.toString());
                //Create the request to TMDB and open connection
                urlConnection = (HttpURLConnection) url.openConnection();
                urlConnection.setRequestMethod("GET");
                urlConnection.connect();

                //Read the input stream into a string
                InputStream inputStream = urlConnection.getInputStream();
                StringBuffer buffer = new StringBuffer();
                if (inputStream == null) {
                    //Nothing to do
                    return null;
                }
                bufferedReader = new BufferedReader(new InputStreamReader(inputStream));
                String line;
                while ((line = bufferedReader.readLine()) != null) {
                    //Make debugging easier by adding a new line to the bufffer stream
                    buffer.append(line + "\n");
                    int result = 1;
                }

                if (buffer.length() == 0) {
                    //stream was empty. No point in parsing.
                    return null;
                }
                movieJsonStr = buffer.toString();

            } catch (IOException e) {
                Log.e(LOG, "Error ", e);
                //If code didnt get the movie data, no point in parsing
                return null;
            } finally {
                if (urlConnection != null) {
                    urlConnection.disconnect();
                }
                if (bufferedReader != null) {

                    try {
                        bufferedReader.close();
                    } catch (final IOException e) {
                        Log.e(LOG, "Error closing stream ", e);
                    }
                }
            }
            try {
                return getMovieJson(movieJsonStr);
            } catch (JSONException e) {
                Log.e(LOG, e.getMessage(), e);
                e.printStackTrace();
            }
                return null;
        }


        @Override
        protected void onPostExecute(String[] result){
            if (result != null){
                mMovieAdapter.clear();
                for (String results : result  ){
                    mMovieAdapter.setMovieData(results);
                }
            }
        }



    }

}

这是我的适配器

package com.xxcanizeusxx.erick.moviesnow;

import android.app.Activity;
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.ImageView;
import android.widget.TextView;

import com.squareup.picasso.Picasso;

import java.util.ArrayList;

/**
 * This class is the MovieAdapter that will take data from the model and
 * display it on the View. Additionally, this adapter will load the picasso base_img_url
 * to populate the griView according to Udacity.
 */

public class MovieAdapter extends ArrayAdapter<Movie> {
    private final String BASE_IMAGE_URL = "http://image.tmdb.org/t/p/w185";
    private Context mContext;
    private int resource;
    private ArrayList<Movie> mMovieData = new ArrayList<Movie>();

    //Constructor matching super
    public MovieAdapter(Context mContext, int resource, ArrayList<Movie> mMovieData) {
        super(mContext, resource, mMovieData);
        this.mContext = mContext;
        this.resource = resource;
        this.mMovieData = mMovieData;

    }

    //This method sets the movieData and refreshes the gridLayout items.
    public void setMovieData(ArrayList<Movie> mMovieData){
        this.mMovieData = mMovieData;
        //Notifies if data state has changed
        notifyDataSetChanged();
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent){
        //Declare the variables to hold the convertView and viewHolder static class
        View cv = convertView;
        ViewHolder viewHolder;

        //If the convertView is null, we don't have a view so, create one.
        if(cv == null){
            //Create the View
            cv = LayoutInflater.from(getContext()).inflate(resource, parent, false);
            //Call the static viewHolder class
            viewHolder = new ViewHolder();
            //Initialize the textView and imageView to load inside the view
            viewHolder.movieTextView = (TextView) cv.findViewById(R.id.movie_title);
            viewHolder.moviePoster = (ImageView) cv.findViewById(R.id.movie_poster);
            cv.setTag(viewHolder);
        }else{
            viewHolder = (ViewHolder) cv.getTag();
        }

        Movie movieItem = mMovieData.get(position);
        //Set the textView holder
        viewHolder.movieTextView.setText(movieItem.getTitle());
        //use picasso to load images to the holder
        Picasso.with(mContext).load(BASE_IMAGE_URL + movieItem.getPoster_path()).fit().into(viewHolder.moviePoster);
        return cv;

    }

    static class ViewHolder{
        TextView movieTextView;
        ImageView moviePoster;

    }
}

这是我的主要活动

package com.xxcanizeusxx.erick.moviesnow;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        if(savedInstanceState == null){
            getSupportFragmentManager().beginTransaction()
                    .add(R.id.container, new MovieFragment())
                    .commit();
        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu){
        //Inflate the menu, this adds items to actionbar if present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item){
        int id = item.getItemId();
        if (id == R.id.action_settings){
            return true;
        }
        return  super.onOptionsItemSelected(item);
    }
}

我的girdLayout xml

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
             android:id="@+id/grid_layout"
              android:orientation="vertical"
              android:layout_width="match_parent"
              android:layout_height="match_parent">
    <GridView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/gridView"
        android:numColumns="2"
        android:gravity="center"
        android:drawSelectorOnTop="true"
        android:verticalSpacing="5dp"
        android:horizontalSpacing="5dp">
    </GridView>

</FrameLayout>

我的movieItem xml（用于填充gridLayout）

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
              android:id="@+id/movie_detail_item"
              android:orientation="vertical"
              android:layout_width="wrap_content"
              android:layout_height="wrap_content">
    <ImageView
        android:id="@+id/movie_poster"
        android:layout_width="100dp"
        android:layout_height="100dp"
        android:scaleType="fitXY"/>

    <TextView
        android:id="@+id/movie_title"
        android:maxLines="2"
        android:gravity="center"
        android:textSize="14sp"
        android:textAllCaps="true"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"/>

</LinearLayout>

Answer 1

首先更改您的Asynctask的参数

public class FetchMovieTask extends AsyncTask<Void, String[], String[]> {}

然后更改doInBackground()的返回类型以获取结果

@Override
protected String[] doInBackground(Void... params) {}

了解参数和返回类型的流程。

更新：

@Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
rootView = inflater.inflate(R.layout.gird_layout, container, false);

        //Initialize our array adapter
        mMovieData = new ArrayList<>();
        updateView(mMovieData);
        return rootView;
    }


void updateView(ArrayList<>() movieData){
mMovieAdapter = new MovieAdapter(getActivity(), R.layout.grid_movie_item, movieData);

        //Get a reference to the gridView and attach the adapter to it
        GridView mGridView = (GridView) rootView.findViewById(R.id.gridView);
        mGridView.setAdapter(mMovieAdapter);
}

从GetMovie和DoInBackground返回ArrayList

 @Override
protected ArrayList<Movies> doInBackground(Object... params) {}

和

private ArrayList<Movies> getMovieJson(String movieJsonStr) throws JSONException {
....
mMovieData.add(movieItem);
return mMovieData;
}

调用此updateView来更新setAdapater(..)并将postExecute参数更新为

@Override
        protected void onPostExecute(ArrayList<Movies> movieData){
            updateView(movieData);
        }

Answer 2

首先要进行代码编译吗？ 据我所知，您的AsyncTask具有以下签名-

public class FetchMovieTask extends AsyncTask<String[], Void, Void> {

但是您是从doInBackground返回String []的，理想情况下会给您一个错误。 无论如何，在这种情况下，您不必从AsyncTask返回任何内容。 只需在onPostExecute上添加此调用mMovieAdapter.setMovieData(Arrays.asList(result))

顺便说一句，类型结果应该是String []而不是我所看到的String。