每当在我的Popular Movies Udacity项目中，我都会在收藏夹电影收藏集中的电影海报上单击，该收藏夹电影已脱机维护为数据库，URL列表会正确更新，但AsyncTask中创建的JSONArray不会立即更新。 / p>
package com.example.android.popularmovies;
import android.database.Cursor;
import android.os.AsyncTask;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.GridLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.util.Log;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.ProgressBar;
import android.widget.TextView;
import com.example.android.popularmovies.Database.Contract;
import com.example.android.popularmovies.utilities.NetworkUtils;
import com.facebook.stetho.Stetho;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import java.io.IOException;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.ArrayList;
public class MainActivity extends AppCompatActivity {
private final static String BASE_POSTER_URL = "http://image.tmdb.org/t/p/w500/";
private static String OPTION = "OPTION";
TextView mNoFavorites;
// = new JSONArray();
JSONArray favoriteJsonArray;
int optionChosen;
private ProgressBar mProgessBar;
private TextView mErrorMessage;
private Button mRetry;
private RecyclerView mRecyclerView;
private RecyclerView.Adapter mAdapter;
private URL url;
private ArrayList<String> posterList;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if (savedInstanceState != null)
optionChosen = savedInstanceState.getInt(OPTION);
Stetho.initializeWithDefaults(this);
setContentView(R.layout.activity_main);
mRecyclerView = findViewById(R.id.my_recycler_view);
mRecyclerView.setHasFixedSize(true);
RecyclerView.LayoutManager mLayoutManager = new GridLayoutManager(this, 2);
mRecyclerView.setLayoutManager(mLayoutManager);
//mAdapter = new MainActivityAdapter(this, posterList, null);
//mRecyclerView.setAdapter(mAdapter);
mProgessBar = findViewById(R.id.progess_bar);
mErrorMessage = findViewById(R.id.error_message);
mRetry = findViewById(R.id.retry);
mNoFavorites = findViewById(R.id.no_favorites_yet);
favoriteJsonArray = new JSONArray();
tryToConnect(new View(this));
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
MenuInflater inflater = getMenuInflater();
inflater.inflate(R.menu.preferences, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
try {
if (item.getItemId() == R.id.top_rated) {
mRecyclerView.setVisibility(View.VISIBLE);
mNoFavorites.setVisibility(View.INVISIBLE);
url = NetworkUtils.buildUrl("top_rated");
if (url != null) {
mErrorMessage.setVisibility(View.INVISIBLE);
mRetry.setVisibility(View.INVISIBLE);
new FetchMovies().execute(url, null, null);
}
optionChosen = 1;
}
if (item.getItemId() == R.id.most_popular) {
mRecyclerView.setVisibility(View.VISIBLE);
mNoFavorites.setVisibility(View.INVISIBLE);
url = NetworkUtils.buildUrl("most_popular");
if (url != null) {
mErrorMessage.setVisibility(View.INVISIBLE);
mRetry.setVisibility(View.INVISIBLE);
new FetchMovies().execute(url, null, null);
}
optionChosen = 2;
}
if (item.getItemId() == R.id.favorites) {
optionFavorites();
optionChosen = 3;
}
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (java.lang.NullPointerException e) {
e.printStackTrace();
}
return super.onOptionsItemSelected(item);
}
@Override
protected void onResume() {
super.onResume();
if (optionChosen == 3)
optionFavorites();
}
@Override
public void onSaveInstanceState(Bundle savedInstanceState) {
// Save the user's current game state
savedInstanceState.putInt(OPTION, optionChosen);
// Always call the superclass so it can save the view hierarchy state
super.onSaveInstanceState(savedInstanceState);
}
/* public void onRestoreInstanceState(Bundle savedInstanceState) {
// Always call the superclass so it can restore the view hierarchy
super.onRestoreInstanceState(savedInstanceState);
// Restore state members from saved instance
optionChosen = savedInstanceState.getInt(OPTION);
}
*/
private void optionFavorites() {
try {
String[] projection = {"movie_id", "favorite_poster_path"};
Cursor cursor = getContentResolver().query(
Contract.FavoriteMovieDatabase.CONTENT_URI,
projection,
null,
null,
null
);
ArrayList<String> posterPathArrayList = new ArrayList<>();
ArrayList<URL> urlArrayList = new ArrayList<>();
if (cursor != null && cursor.moveToFirst()) {
do {
String posterPath = cursor.getString(cursor.getColumnIndex(Contract.FavoriteMovieDatabase.FAVORITE_POSTER_PATH));
posterPathArrayList.add(BASE_POSTER_URL + posterPath);
int movieId = cursor.getInt(cursor.getColumnIndex("movie_id"));
URL favoriteURL = NetworkUtils.buildUrl("favorites", movieId);
urlArrayList.add(favoriteURL);
} while (cursor.moveToNext());
Log.d("urllist", "" + urlArrayList.toString());
new FetchFavorites().execute(urlArrayList, null, null);
mAdapter = new MainActivityAdapter(MainActivity.this, posterPathArrayList, favoriteJsonArray);
mRecyclerView.setAdapter(mAdapter);
} else {
mRecyclerView.setVisibility(View.INVISIBLE);
mNoFavorites.setVisibility(View.VISIBLE);
}
} catch (java.lang.NullPointerException e) {
e.printStackTrace();
} catch (MalformedURLException e) {
e.printStackTrace();
}
}
private void noConnection() {
mErrorMessage.setText(R.string.no_connection);
mErrorMessage.setVisibility(View.VISIBLE);
mRetry.setText(R.string.retry);
mRetry.setVisibility(View.VISIBLE);
}
public void tryToConnect(View v) {
try {
url = NetworkUtils.buildUrl("most_popular");
} catch (MalformedURLException e) {
e.printStackTrace();
}
if (url != null) {
mErrorMessage.setVisibility(View.INVISIBLE);
mRetry.setVisibility(View.INVISIBLE);
new FetchMovies().execute(url, null, null);
}
}
private class FetchMovies extends AsyncTask<URL, Void, String> {
@Override
protected void onPreExecute() {
super.onPreExecute();
mProgessBar.setVisibility(View.VISIBLE);
}
@Override
protected String doInBackground(URL... params) {
URL searchUrl = params[0];
String searchResults = null;
try {
searchResults = NetworkUtils.getResponseFromHttpUrl(searchUrl);
} catch (IOException e) {
e.printStackTrace();
}
return searchResults;
}
@Override
protected void onPostExecute(String searchResults) {
mProgessBar.setVisibility(View.INVISIBLE);
try {
posterList = new ArrayList<>();
if (searchResults != null && !searchResults.equals("")) {
JSONObject jsonObject = new JSONObject(searchResults);
JSONArray pageOne = jsonObject.getJSONArray("results");
int length = pageOne.length();
for (int i = 0; i < length; i++) {
JSONObject result = pageOne.getJSONObject(i);
String posterPath = BASE_POSTER_URL + result.getString("poster_path");
posterList.add(posterPath);
}
mAdapter = new MainActivityAdapter(MainActivity.this, posterList, pageOne);
mRecyclerView.setAdapter(mAdapter);
} else noConnection();
} catch (Exception e) {
e.printStackTrace();
}
}
}
private class FetchFavorites extends AsyncTask<ArrayList<URL>, Void, ArrayList<String>> {
@Override
protected ArrayList<String> doInBackground(ArrayList<URL>... params) {
ArrayList<URL> urlArrayList = params[0];
ArrayList<String> stringArrayList = new ArrayList<>();
String searchResults;
URL searchUrl;
favoriteJsonArray = new JSONArray();
for (int i = 0; i < urlArrayList.size(); i++)
try {
searchUrl = urlArrayList.get(i);
searchResults = NetworkUtils.getResponseFromHttpUrl(searchUrl);
stringArrayList.add(searchResults);
} catch (IOException e) {
e.printStackTrace();
}
return stringArrayList;
}
@Override
protected void onPostExecute(ArrayList<String> stringArrayList) {
for (int i = 0; i < stringArrayList.size(); i++)
try {
favoriteJsonArray.put(new JSONObject(stringArrayList.get(i)));
} catch (JSONException e) {
e.printStackTrace();
}
}
}
}
urlArrayList可以正确更新，但是AsyncTask内部更新的favoriteJsonArray却没有。为什么？
答案 0 :(得分：0)
您的代码中有两个问题：
，在FetchFavorites.doInBackground()中，您为new JSONArray()分配了favoriteJsonArray，但是您的mAdapter仍然保留着旧的引用，即一个空的JSONArray。
您在更新mAdapter.notifyDataSetChanged()之后没有致电favoriteJsonArray。
您可以通过以下方式解决问题：
不要在{{1}中使用new JSONArray()，并在更新FetchFavorites.doInBackground()之后调用mAdapter.notifyDataSetChanged()，但是仍然存在问题，您应该清除{{1 }}每次获取新数据并清除favoriteJsonArray都是一种无聊的工作（没有favoriteJsonArray方法）。
JSONArray，但是编辑您的clear()，添加类似new JSONArray()的方法，并为其设置新创建的MainActivityAdapter，然后调用setFavorites(JSONArray array)