I want to make an app lister application which fetches the application list via the packagemanager through an AsyncTask<Void, Void, List<PackageSummary>> nested in a singleton class. However, if and only if I implement the async task, the RecyclerView will not populate on the first OnCreate.
I am sure I am doing a silly mistake and/or do not understand AsyncTask and RecyclerView well enough, but for the love of me I cannot find the root of the issue.
In my toy app repository I have prepared two, relatively cleaner branches for illustration purposes:
One in which the packages are fetched in the main thread, and the recyclerview populates on first Oncreate (git_UI_thread).
One in which an AsyncTask<Void, Void, List<PackageSummary>> class is called. The application persistence is not set yet (on purpose), and the RecyclerView will only populate after the application is rotated (git_background_thread).
For those who are not inclined to click on the bitbucket link above, the code snippet of the inside of my AsyncTask looks like this:
#Override
protected void onPostExecute(List<SingletonPackageSummarySupplier.PackageSummary> packageSummaries) {
super.onPostExecute(packageSummaries);
isQueryingInProgress = false;
packageSummaryList = packageSummaries;
}
#Override
protected List<SingletonPackageSummarySupplier.PackageSummary> doInBackground(Void... voids) {
List<PackageSummary> installedPackages = new ArrayList<>();
Intent intent = new Intent(Intent.ACTION_MAIN, null);
intent.addCategory(Intent.CATEGORY_LAUNCHER);
intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK | Intent.FLAG_ACTIVITY_RESET_TASK_IF_NEEDED);
List<ResolveInfo> resolveInfoList = context.getPackageManager().queryIntentActivities(intent, 0);
for (ResolveInfo resolveInfo : resolveInfoList) {
ActivityInfo activityInfo = resolveInfo.activityInfo;
installedPackages.add(new PackageSummary(resolveInfo.activityInfo));
}
return installedPackages;
}
And this is my Main activity OnCreate:
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
psList = SingletonPackageSummarySupplier.getInstance(context).getPackageSummaryListReadOnly();
setContentView(R.layout.activity_main);
recyclerView = (RecyclerView) findViewById(R.id.recycler_view);
recyclerViewLayoutManager = new LinearLayoutManager(context);
recyclerView.setLayoutManager(recyclerViewLayoutManager);
adapter = new AdapterApplist(context, psList);
recyclerView.setAdapter(adapter);
}
And this is how the singleton is fetched:
static SingletonPackageSummarySupplier instance;
public static SingletonPackageSummarySupplier getInstance(Context context) {
if (instance == null) {
instance = new SingletonPackageSummarySupplier(context);
} else{
instance.updateInstance(context);
}
return instance;
}
P.S.: I think (but not sure) the singleton pattern is justified in order to diminish the changes of memory leaks.
P.S.2: I have read a couple questions about this, but none had an accepted / working solution.
There are two steps: Update your data to AdapterApplist and notify it. Hence you should create a new method like:
public void setData(List<SingletonPackageSummarySupplier.PackageSummary> list)
{ //reset your data ere
}
inside AdapterApplist class. Then, update your post:
#Override
protected void onPostExecute(List<SingletonPackageSummarySupplier.PackageSummary> packageSummaries) {
super.onPostExecute(packageSummaries);
isQueryingInProgress = false;
packageSummaryList = packageSummaries;
adapter.setData(packageSummaryList);
adapter.notifyDataSetChanged();
}
Just add adapter.notifyDataSetChanged(); in your postexecute method of AsyncTask
Either I was unable to implement the observer pattern (note that the asynctask was in a singleton class separate from the recyclerview and activity), or it is just not working well in this case.
Anyway, I ended up fixing the issue with the relatively new lifecycle-aware components: MutableLiveData, LiveData and AndroidViewModel (instead of viewmodel, which does not get context as constructor parameter). It is simple and elegant.
The key part was this, in the activity:
PackageSummarySupplier model = ViewModelProviders.of(this).get(PackageSummarySupplier.class);
model.getPackageSummaryList().observe(this, packageSummaryList -> {
adapter = new AdapterApplist(context, packageSummaryList);
recyclerView.setAdapter(adapter);
});
Related
I'm new to SO and fairly new to coding, so please accept my apologies in advance if I break rules or expectations here.
I have an unusual setup involving two recyclerViews, which I'll explain here and also paste a simplified version of the code below (as there is so much not relevant to this question).
In what I'll call verticalRecyclerViewActivity, a verticalRecyclerViewAdapter is called, with data it fetches from Firebase and loads into arrayLists.
If the user clicks on an item in the vertical recyclerview, a new dialog fragment which I'll call horizontalRecyclerViewDialogFragment is inflated, and that loads what I'll call horizontalRecyclerView (which has similar items to the vertical one, in more detail, with options to click on them to review them).
If the user clicks on an item in the horizontalRecyclerView, a new activity which I'll call reviewItem is started (through an Intent). When the user submits their review, it finishes and returns (through the backstack) to the horizontal RecyclerView. That can also happen if they press the back button without actually submitting a review. That all works fine, but I need the horizontalRecyclerView to show that they have (or haven't) reviewed the item and state the score they gave it in a review.
Calling notifyDataSetChanged won't work for this because of how information comes through two recyclerViews and Firebase calls (or, at least, it would be very inefficient).
I've tried using startActivityForResult (I know it's deprecated, but if I could get that to work I could try using the newer equivalent which I don't yet understand) but the problem is that the result is returned to the original (VerticalRecylcerView) activity, which is two recyclerView adapters and one fragment beneath what needs to be updated, and I don't know how to pass that data to the horizontal Recyclerview.
I've also tried using interfaces but was unable to pass it through the Intent (tried using Parcelable and Serializable, but it seems neither can work in this situation?).
Since the review is updated on Firebase, I could have the horizontal Recyclerview listen for a change, but that seems very inefficient?
So I've found a solution using localBroadcast (which I know is also deprecated). The Intent (with the review score) is transmitted when it is reviewed and received in the horizontal recyclerView adapter. But when and how should I unregister the adapter? Ideally the receiver would be turned on when the user goes to the Review activity and turned off once the user returns from that activity and the (horizontal) recyclerView holder is updated, whether the review is successfully submitted or whether the user just presses the back button and never submits a review.
My question is similar to this one: How to unregister and register BroadcastReceiver from another class?
That is noted as a duplicate of this one: How to unregister and register BroadcastReceiver from another class?
There's a lot in those questions I don't understand, but the important difference I think between their and my cases is that I would just like the receiver to know when a review is submitted, and ideally be unregistered then, or possibly when the viewHolder is recycled, which I tried but also didn't work since it's not connected to the viewHolder (should it be?).
Any help would be much appreciated, thank you!
public class verticalRecyclerViewActivity extends AppCompatActivity {
// Loads an XML file and assembles an array from Firebase.
mVerticalRecyclerView = findViewById(R.id.verticalRecyclerView);
verticalRecyclerViewAdaptor mVerticalRecyclerViewAdaptor = new verticalRecyclerViewAdaptor (this); // also pass other information it needs
mVerticalRecyclerView .setAdapter(mVerticalRecyclerViewAdaptor);
}
public class verticalRecyclerViewAdaptor extends RecyclerView.Adapter<verticalRecyclerViewAdaptor.singleHolder> {
// Usual recyclerView content
holder.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
horizontalRecyclerViewFragment mHorizontalRecyclerViewFragment = new horizontalRecyclerViewFragment();
// lots of arguments passed it needs.
FragmentManager fragmentManager = ((FragmentActivity) view.getContext()).getSupportFragmentManager();
mHorizontalRecyclerViewFragment.show(fragmentManager, null);
}
public class mHorizontalRecyclerViewFragment extends DialogFragment {
public Dialog onCreateDialog(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
mContext = getActivity().getApplicationContext(); // Not sure why I need this, but it works.
View horizontalRecyclerViewView = getActivity().getLayoutInflater().inflate(R.layout.horizontal_recyclerview_holder, new CardView(getActivity()), false);
Dialog horizontalRecyclerViewDialog = new Dialog(getActivity());
horizontalRecyclerViewDialog.setContentView(horizontalRecyclerViewView);
mHorizontalRecyclerView = horizontalRecyclerViewView.getRootView().findViewById(R.id.horizontalRecyclerView);
mHorizontalRecyclerViewAdapter = new horizontalRecyclerViewAdapter (mContext)
// Other arguments passed
mHorizontalRecyclerView.setLayoutManager(new LinearLayoutManager(getActivity(),
LinearLayoutManager.HORIZONTAL, false));
mHorizontalRecyclerView.setAdapter(mHorizontalRecyclerViewAdapter);
}
public class horizontalRecyclerViewAdapter extends RecyclerView.Adapter<horizontalRecyclerViewAdapter.horizontalRecyclerViewHolder> {
public horizontalRecyclerViewAdapter(){}
// Blank constructor and also one with lots of arguments for it to work.
public horizontalRecyclerViewAdapter.horizontalRecyclerViewHolder onCreateViewHolder(#NonNull ViewGroup parent, int viewType) {
View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.horizontal_recyclerview_adaptor_holder, parent, false);
return new horizontalRecyclerViewAdapter.horizontalRecyclerViewHolder(view);
}
public void onBindViewHolder(#NonNull horizontalRecyclerViewHolder holder, int position) {
// Connect up various views.
holder.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
LocalBroadcastManager.getInstance(mContext).registerReceiver(reviewSubmittedListener, new IntentFilter("reviewSubmitted"));
Intent reviewNow = new Intent(view.getContext(), ReviewActivity.class);
// Put extra details with the intent
view.getContext().startActivity(reviewNow);
}
BroadcastReceiver reviewSubmittedListener = new BroadcastReceiver() {
#Override
public void onReceive(Context context, Intent reviewFinishedIntent) {
int reviewScore = reviewFinishedIntent.getExtras().getInt("reviewScore");
// Update the horizontal RecyclerView with the information received from the review Activity.
}
};
}
public class ReviewActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_review_item);
// Set up the review, using Firebase and data passed through the intent.
}
public void submitReview() {
// Check that the review is complete/valid and submit it through Firebase
LocalBroadcastManager localBroadcastManager = LocalBroadcastManager.getInstance(ReviewItemActivity.this);
Intent reviewFinishedIntent = new Intent("reviewSubmitted");
reviewFinishedIntent.putExtra("reviewScore", overallScore);
LocalBroadcastManager.getInstance(this).sendBroadcast(reviewFinishedIntent);
finish();
}
If you are using RxJava you can use the RxBus else you can use one of many EventBus implementation for this.
If that is not the path you want to take then you can have a shared view model object that can be used only for communication between fragments see this article.
PlaylistFragment starts an adapter:
playlistsAdapter = new PlaylistRecyclerAdapter(playlistsListArray, addToPlaylist, mSong, getActivity(), this);
PlaylistRecyclerAdapter binds data to the PlaylistViewHolder, something like this:
((PlaylistViewHolder) viewHolder).bind(this, dataSet.get(position), addToPlaylist, mSong);
User clicks on an item in PlaylistViewHolder:
context.startActivity(PublicPlaylistActivity.createStartIntent(context, playlist));
Now here is the question, how can PublicPlaylistActivity talk back to the initial PlaylistFragment?
I suggest you'd better use Interface from fragment to adapter. So when user clicks anything in adapter, call function realization in fragment. If you need your activity to proceed some operation - ((YourActivity) getActivity()).someMethod() should be called from fragment.
Second trick is using broadcastreceiver to send events. A bit more complicated. You have to launch broadcast in view you need to recive message and send these messages from adapter. This approach is more complexible to debug and support if system is wide spread, so you'd better use interfaces.
There are several ways of doing that. The simplest way should be starting the PublicPlaylistActivity with startActivityForResult. In that way, then the activity finishes, you can set send some data to the caller fragment (which is PlaylistFragment in your case). Here is a nice tutorial about the implementation.
Another way of doing that is by using lifecycle methods. You might have a public static variable which can keep track of some status that you might observe in your onResume function of your PlaylistFragment when you are returning back from your PublicPlaylistActivity. You might consider a sample implementation as follows.
Define a public static variable in your PlaylistFragment. Then in your onResume function check the value of that variable and take actions accordingly.
public static boolean someIndicator = false; // Initialize with a default value
#Override
protected void onResume() {
super.onResume();
if(someIndicator == true) doSomething();
else doSomethingElse();
}
Now you can set the indicator variable from anywhere in your application actually which will have the effect on your PlaylistFragment. For example, from your PublicPlaylistActivity, you might consider doing something like this.
public void someFunctionInYourPublicPlaylistActivity() {
// ...
// Some code and then the following
PlaylistFragment.someIndicator = true;
}
Another way of achieving the same thing is by using a BroadcastReceiver. Here is a tutorial on how you can implement one.
It really depends on how you are structuring your whole activity-fragments communication. Hope that helps!
I would do a common "context" class (ComContext) with an interface. When you create your fragment, you also create this class. And from the activity you can check if it exists or not.
I assume that you already have a helper(AppHelper) class with static variables.
public class AppHelper {
public static ComContext comContext = null;
}
public class MainFragment {
#Override
public void onViewCreated(#NonNull View view, #Nullable Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
ConContext comContext = new ComContext();
comContext.listener = this;
AppHelper.comContext = comContext;
}
#Override
public void onDataChanged() {
}
#Override
public void onDestroyView() {
super.onDestroyView();
AppHelper.comContext = null;
}
}
public class MainActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if (AppHelper.comContext != null) {
AppHelper.comContext.listener.onDataChanged();
}
}
}
public class ComContext {
public interface HelperListener {
void onDataChanged();
}
public HelperListener listener = null;
}
I'm trying to make an method executable everytime the fragment appears. I have a MainActivity and a PagerAdapter and inside PagerAdapter, I have Fragments so my problem is that I placed a method inside my onCreate of Fragment but it's executing only once. Maybe the onCreate of Activity and Fragment both have roles here. After searching about a similar question I found this :
#Override
public void setUserVisibleHint(boolean isVisibleToUser) {
super.setUserVisibleHint(isVisibleToUser);
if (isVisibleToUser) {
// Do your Work
} else {
// Do your Work
}
}
But when I am putting my method here am getting a NullPointerException. My method:
public void retrieveLocalStoredNotes() {
notesArray = new ArrayList<String>();
notesIDArray = new ArrayList<String>();
for (NotesRealmClass note : NotesQueryRealm) {
notesArray.add(note.getTitle());
notesIDArray.add(note.getobjectId());
}
notesAdapter = new NotesAdapter(getActivity(), getData());
recyclerView.setAdapter(notesAdapter);
recyclerView.setLayoutManager(new LinearLayoutManager(getActivity()));
}
Maybe am getting this error because I am initialising the variables in onCreate and setVisibleHint and it is running before onCreate. How can I make this workable or is my approach not enough for that.
Call your method in onResume() method.
I have an Activity with a Recycler view handling cards. I have a SwipeRefreshLayout so when I swipe it updates the RecyclerView with new content. So far, so good.
Howerver, I want to update the RecyclerView every X seconds so if, for instance, I leave the activity with the recylcerview opened and I forgot to swipe it, it would as well update by itself.
To do that, I thought something like this:
( I ommitted necessary code ).
My main Activity which contains the recyclerview schedules a Job like this:
private void scheduleJob() {
ComponentName serviceName = new ComponentName(this, MyJobService.class);
JobInfo jobInfo = new JobInfo.Builder(JOB_ID, serviceName)
.setRequiredNetworkType(JobInfo.NETWORK_TYPE_UNMETERED)
.setRequiresDeviceIdle(false)
.setRequiresCharging(false)
.setPeriodic(3000)
//.setOverrideDeadline(400) // Remove comment for faster testing.
.build();
JobScheduler scheduler = (JobScheduler) getSystemService(Context.JOB_SCHEDULER_SERVICE);
int result = scheduler.schedule(jobInfo);
if (result == JobScheduler.RESULT_SUCCESS) {
Toast.makeText(this,"Start", Toast.LENGTH_LONG).show();
} } }
Inside MyJobService I through a Broadcast to my Activity, to let it know it has to update the content of the RecylcerView.
The responsable of receiving the broadcast is an inner class like this:
public static class MyReceiver extends BroadcastReceiver{
#Override
public void onReceive(Context context, Intent intent) {
DataSource dataSource = new DataSource(context);
items = dataSource.getItems(); // can't do this due to outter class variable
adapter.refresh(ítems); // can't do this due to outter class variable
Toast.makeText(context,"event",Toast.LENGTH_SHORT).show();
}
}
Problem is on my main Activity I hold two private variable called items (which is the ArrayList ) and adapter ( which is the adapter of the recylcerview) I pass items to the adapter to update the recyclerView content.However, as I am in a static inner class I can’t access outter class variables.
Whats the correct way to do something like this? I think I am messing too much and I guess there must be an easiest and more straight forward way to accomplish what I want.
Thank you very much
Well, turns out I was complicating things too much. It can be done with a simple Handler like this:
// Create the Handler object (on the main thread by default)
Handler handler = new Handler();
// Define the code block to be executed
private Runnable runnableCode = new Runnable() {
#Override
public void run() {
// Do something here on the main thread
Toast.makeText(getApplicationContext(),"Update",Toast.LENGTH_SHORT).show();
ItemsDS itemsDS = new ItempsDS(getApplicationContext());
items = itemsDS.getItems();
adapter.clear();
adapter.addAll(items);
handler.postDelayed(runnableCode, 1000);
}
};
There are Two ways to do this thing:
First is as mentioned by #akshayBhat, you can do it by removing static keyword from BroadcastReceiver class:
ArrayList<String> items;
Adapter adapter;
public class MyReceiver extends BroadcastReceiver {
#Override
public void onReceive(Context context, Intent intent) {
DataSource dataSource = new DataSource(context);
items = dataSource.getItems(); // can't do this due to outter class variable
adapter.refresh(ítems); // can't do this due to outter class variable
Toast.makeText(context, "event", Toast.LENGTH_SHORT).show();
}
}
Second is to pass the reference of current activity state to the BroadCast Receiver and access ClassVariables there using that refernce;
ArrayList<String> items;
Adapter adapter;
public static class MyReceiver extends BroadcastReceiver {
AboutUs mContext;
#Override
public void onReceive(Context context, Intent intent) {
mContext = (AboutUs)context;
DataSource dataSource = new DataSource(context);
mContext.items = dataSource.getItems(); // can't do this due to outter class variable
mContext.adapter.refresh(ítems); // can't do this due to outter class variable
Toast.makeText(context, "event", Toast.LENGTH_SHORT).show();
}
}
I'm trying to show interstitials at the end of some Activities. The problem is the interstitials seem to prevent the Activities from being garbage collected causing an out-of-memory exception. How do i resolve this? Thanks in advance.
public class AdActivity extends FragmentActivity{
//...
protected InterstitialAd interstitial;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
//...
// Create the interstitial.
interstitial = new InterstitialAd(this);
interstitial.setAdUnitId(INTERSTITIAL_UNIT_ID);
// Create ad request.
AdRequest adRequest2 = new AdRequest.Builder().addTestDevice(AdRequest.DEVICE_ID_EMULATOR)
.addTestDevice(deviceId)
.build();
// Begin loading interstitial.
interstitial.loadAd(adRequest2);
}
#Override
public void onPause() {
super.onPause();
displayInterstitial();
}
public void displayInterstitial() {
if (interstitial.isLoaded() && System.currentTimeMillis() >= lastInterstitial + timeLag * 1000) {
lastInterstitial = System.currentTimeMillis();
interstitial.show();
}
}
And i used it like:
public class ActivityA extends AdActivity{ //...
}
Ok i seem to have fixed it by changing
interstitial = new InterstitialAd(this);
to
interstitial = new InterstitialAd(getApplicationContext());
I don't completely understand memory management in java/android but I think whats going on is because the Activity references interstitial and interstitial has a reference to Activity so neither gets garbage-collected. Passing in the application context rather than the Activity context prevents this cycle dependency and solves the problems. Hope this helps someone :D.
One thing that helped me is to invoke the interstitial.show() on the uithread (since i guess its UI-stuff u have to do it on the ui-thread)
Just use application global context:
interstitial = new InterstitialAd(getApplication());
Don't use getApplicationContext(), because returned value will be your current activity.