我刚接触Android开发,确实需要您的帮助。我的问题出在下面的MainActivity
中。该应用实质上是在主要活动中显示电影列表,并在另一个活动中显示电影详细信息。问题是,每当用户从MovieActivity
返回到MainActivity
时,尽管电影已经存在,但加载器会再次开始加载数据。然后它无法停止加载数据。真烦人。我想摆脱这个。因此,当用户返回MainActivity时,加载程序会知道已经加载了数据,不会再加载任何内容。如果有帮助,请参阅我的完整 GitHub存储库 https://github.com/mateuszwojnarowicz/PopularMovies < / p>
我被困了大约3周,并尝试了数百种可能的解决方案。似乎没有任何作用。我感到非常绝望。
非常感谢您的帮助,
马修
public class MainActivity extends AppCompatActivity implements LoaderManager.LoaderCallbacks<String> {
private MovieAdapter mAdapter;
private ArrayList<Movie> mMoviesCollection;
private SharedPreferences sharedPreferences;
private Resources resources;
private LoaderManager loaderManager;
private Loader<String> loader;
private RecyclerView.LayoutManager layoutManager;
private String sortBy;
@BindView(R.id.pb)
ProgressBar progressBar;
@BindView(R.id.er)
TextView errorTextView;
@BindView(R.id.rv)
RecyclerView recyclerView;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
ButterKnife.bind(this);
mMoviesCollection = new ArrayList<Movie>();
sharedPreferences = getSharedPreferences(Constants.SHARED_PREFS, Activity.MODE_PRIVATE);
resources = getResources();
sortBy = sharedPreferences.getString(Constants.KEY_SORT, null);
setSharedPref();
layoutManager = new GridLayoutManager(this, calculateNoOfColumns(this));
loaderManager = getLoaderManager();
loader = loaderManager.getLoader(Constants.LOADER_MOVIES_ID);
initialize();
makeOperationLoadMovies(sortBy);
}
public static int calculateNoOfColumns(Context context) {
DisplayMetrics displayMetrics = context.getResources().getDisplayMetrics();
float dpWidth = displayMetrics.widthPixels / displayMetrics.density;
int noOfColumns = (int) (dpWidth / 150);
return noOfColumns;
}
//Set first-launch pref and set title according to pref
private void setSharedPref(){
if(!sharedPreferences.contains(Constants.KEY_SORT)) {
saveData(Constants.VALUE_POP);
setTitle(resources.getString(R.string.title_pop));
} else {
if (Objects.equals(sharedPreferences.getString(Constants.KEY_SORT, null), Constants.VALUE_POP)) {
setTitle(resources.getString(R.string.title_pop));
}
if (Objects.equals(sharedPreferences.getString(Constants.KEY_SORT, null), Constants.VALUE_TOP)) {
setTitle(resources.getString(R.string.title_top));
}
}
}
//Set up the RecyclerView
private void initialize(){
recyclerView.setLayoutManager(layoutManager);
recyclerView.setHasFixedSize(true);
mMoviesCollection = new ArrayList<>();
mAdapter = new MovieAdapter(mMoviesCollection, this, this);
recyclerView.setAdapter(mAdapter);
}
private void makeOperationLoadMovies(String SORT_BY){
Bundle bundle = new Bundle();
bundle.putString(Constants.LOADER_MOVIES_EXTRA, SORT_BY);
if(recyclerView.isDirty()){
}
else if(loader==null){
loaderManager.initLoader(Constants.LOADER_MOVIES_ID, bundle, this);
}else{
loaderManager.restartLoader(Constants.LOADER_MOVIES_ID, bundle, this);
}
}
//Update shared pref
private void saveData(String SORT_VALUE){
SharedPreferences.Editor editor = sharedPreferences.edit();
editor.putString(Constants.KEY_SORT, SORT_VALUE);
editor.apply();
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
MenuInflater inflater = getMenuInflater();
inflater.inflate(R.menu.main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
int id = item.getItemId();
switch (id){
case R.id.menu_fav:
startActivity(new Intent(MainActivity.this, FavoritesActivity.class));
break;
case R.id.menu_pop:
saveData(Constants.VALUE_POP);
Toast.makeText(this, resources.getString(R.string.message_popularity),Toast.LENGTH_LONG).show();
break;
case R.id.menu_top:
saveData(Constants.VALUE_TOP);
Toast.makeText(this, resources.getString(R.string.message_rating),Toast.LENGTH_LONG).show();
break;
}
return super.onOptionsItemSelected(item);
}
@Override
protected void onPause() {
super.onPause();
Parcelable recyclerViewState;
recyclerViewState = recyclerView.getLayoutManager().onSaveInstanceState();//save
recyclerView.getLayoutManager().onRestoreInstanceState(recyclerViewState);
}
@Override
protected void onPostResume() {
super.onPostResume();
Parcelable recyclerViewState;
recyclerViewState = recyclerView.getLayoutManager().onSaveInstanceState();//save
recyclerView.getLayoutManager().onRestoreInstanceState(recyclerViewState);
}
@SuppressLint("StaticFieldLeak")
@Override
public Loader<String> onCreateLoader(int id, final Bundle args) {
return new AsyncTaskLoader<String>(this) {
@Override
protected void onStartLoading() {
super.onStartLoading();
forceLoad();
progressBar.setVisibility(View.VISIBLE);
errorTextView.setVisibility(View.INVISIBLE);
}
@Override
public void deliverResult(String data) {
super.deliverResult(data);
}
@Override
public String loadInBackground() {
String jsonString = "";
URL url = NetworkUtils.buildUrl(args.getString(Constants.LOADER_MOVIES_EXTRA));
try {
jsonString += NetworkUtils.getResponseFromHttpUrl(url);
} catch (IOException e) {
e.printStackTrace();
}
if(jsonString.isEmpty()){
} else {
try {
JSONObject jsonObject = new JSONObject(jsonString);
JSONArray jsonArray = jsonObject.getJSONArray(Constants.JSON_KEY_MOVIE_RESULTS);
for (int i = 0; i < jsonArray.length(); i++) {
//Get 1 movie from JSON
String mTitle;
int mId;
String mPosterUrl;
String mPlot;
double mUserRating;
String mReleaseDate;
JSONObject Jmovie = (JSONObject) jsonArray.get(i);
mTitle = Jmovie.getString(Constants.JSON_KEY_MOVIE_TITLE);
mId = Jmovie.getInt(Constants.JSON_KEY_MOVIE_ID);
mPosterUrl = NetworkUtils.getPosterString(Jmovie.getString(Constants.JSON_KEY_MOVIE_POSTER_PATH));
mPlot = Jmovie.getString(Constants.JSON_KEY_MOVIE_OVERVIEW);
mUserRating = Jmovie.getDouble(Constants.JSON_KEY_MOVIE_VOTE_AVERAGE);
mReleaseDate = Jmovie.getString(Constants.JSON_KEY_MOVIE_RELEASE_DATE);
//Get videos
ArrayList<Video> mVideos = new ArrayList<Video>();
URL videosURL = NetworkUtils.buildUrlVideos(String.valueOf(mId));
String videosJSON = NetworkUtils.getResponseFromHttpUrl(videosURL);
JSONObject jsonObjectVideos = new JSONObject(videosJSON);
JSONArray jsonArrayVideos = jsonObjectVideos.getJSONArray(Constants.JSON_KEY_VIDEO_RESULTS);
if(jsonArrayVideos.length()==0){
mVideos = null;
} else {
for(int v = 0; v < jsonArrayVideos.length(); v++){
JSONObject Jvideo = (JSONObject) jsonArrayVideos.get(v);
String mVideoName;
String mVideoUrlString;
mVideoName = Jvideo.getString(Constants.JSON_KEY_VIDEO_NAME);
mVideoUrlString = "https://www.youtube.com/watch?v="+Jvideo.getString(Constants.JSON_KEY_VIDEO_KEY);
Video video = new Video(mVideoName, mVideoUrlString);
mVideos.add(video);
}
}
//GetReviews
ArrayList<Review> mReviews = new ArrayList<Review>();
URL reviewsURL = NetworkUtils.buildUrlReviews(String.valueOf(mId));
String reviewsJSON = NetworkUtils.getResponseFromHttpUrl(reviewsURL);
JSONObject jsonObjectReviews = new JSONObject(reviewsJSON);
JSONArray jsonArrayReviews = jsonObjectReviews.getJSONArray(Constants.JSON_KEY_REVIEW_RESULTS);
if(jsonArrayReviews.length()!=0) {
for(int r = 0; r < jsonArrayReviews.length(); r++){
JSONObject Jreview = (JSONObject) jsonArrayReviews.get(r);
String mReviewName;
String mReviewText;
mReviewName = Jreview.getString(Constants.JSON_KEY_REVIEW_AUTHOR);
mReviewText = Jreview.getString(Constants.JSON_KEY_REVIEW_CONTENT);
Review review = new Review(mReviewName, mReviewText);
mReviews.add(review);
}
}
Movie movie = new Movie(mTitle, mId, mPosterUrl, mPlot, mUserRating, mReleaseDate, mVideos, mReviews);
mMoviesCollection.add(movie);
}
} catch (JSONException e) {
e.printStackTrace();
} catch (IOException e){
e.printStackTrace();
}
}
return null;
}
};
}
@Override
public void onLoadFinished(Loader<String> loader, String data) {
progressBar.setVisibility(View.GONE);
mAdapter.notifyDataSetChanged();
}
@Override
public void onLoaderReset(Loader<String> loader) {
}
}
答案 0 :(得分:1)
因为您是Android新手,所以有很多错误。因此,很多人可能不想插话。无论如何,我也是新手,并且与您现在处于同一班级,所以我给您一个机会。
首先,您的加载程序未返回正确的数据类型。您的加载程序应为Loader<List<Movie>>
,并且应返回new AsyncTaskLoader<List<Movie>>
。您想要这样做的原因是要利用AsyncTaskLoader提供的一切。我会进一步解释。
第二,通过将初始引用从Activity移到加载器中,我们将在加载器中缓存数据。
因此,将private ArrayList<Movie> mMoviesCollection;
移动为AsyncTaskLoader的实例变量。从onCreate和initialize方法中删除行mMoviesCollection = new ArrayList<Movie>();
。
在AsyncTaskLoader中,您需要在forceLoad之前检查onStartLoading中是否已经存在数据,并实现deliverResult。
因此,您的onStartLoading()应该如下所示:
@Override
protected void onStartLoading() {
super.onStartLoading();
if(mMoviesCollection.isEmpty()){
forceLoad();
progressBar.setVisibility(View.VISIBLE);
errorTextView.setVisibility(View.INVISIBLE);
} else {
deliverResult(mMoviesCollection)
}
}
您的deliveryResult应该如下所示:
@Override
public void deliverResult(List<Movie> data) {
mMoviesCollection = data;
super.deliverResult(data);
}
现在,您需要实现一个setData(List<Movie> movies)
方法,该方法设置适配器的数据实例变量并在适配器中调用notifyDataSetChanged()
。像这样:
public void setData(List<Movie> movies){
mMovies = movies;
notifyDataSetChanged();
}
从适配器的构造函数中删除List<Movie>
。这样,您可以构建适配器而无需任何数据。如果数据为null,则适配器的getItemCount()
应该返回0,并且recyclerView将不会尝试构建视图。
完成后,您可以像这样调用onLoadFinished:
@Override
public void onLoadFinished(Loader<List<Movie>> loader, List<Movie> data) {
progressBar.setVisibility(View.GONE);
mAdapter.setData(data);
}
编辑:更正了将ArrayList实例化为Instance变量的问题。您不能在那里实例化mMoviesCollection,然后稍后再实例化,或者仅使用mMoviesCollection.isEmpty()来检查其是否为空,正如我在onStartLoading中所做的更改一样::
编辑: 您需要弄清楚您的库,在某些地方使用android.app,在其他地方使用android.support。
因此,在您的导入中更改以下内容:
import android.app.LoaderManager;
import android.content.AsyncTaskLoader;
import android.content.Loader;
全部到:
import android.support.v4.app.LoaderManager;
import android.support.v4.content.AsyncTaskLoader;
import android.support.v4.content.Loader;
现在,TMDB.org API的请求限制为每10秒40个请求。 https://developers.themoviedb.org/3/getting-started/request-rate-limiting
因此,您的加载程序甚至无法完成所有操作,并引发异常。建议您在调用视频并评论进入MovieActivity时分手,方法是在其中创建另一个AsyncTaskLoader并在加载详细信息屏幕时分别调用它们。
从技术上讲,您也可以将Thread.sleep(300)或更少的内容添加到AsyncTaskLoader中,但这会使它变得非常慢。换句话说,您必须将数据推送到10秒标记之后才能完全加载。
现在,有了这些以及我们所做的更改,一切都会在配置更改(例如屏幕旋转)中保留下来。
如果您希望数据能够继续生存下去,则必须以某种方式保留数据。就像将json响应另存为onSaveInstanceState中的字符串或将JSon String保存至您创建的数据库一样。