Develop Reference

RecyclerView onBindViewHolder called only once inside Tab layout

I've four tabs and four fragments (each one for each tab).
Each fragment has a vertical recycler view. Since all fragments view look similar I'm re-using the same layout file, same recycler view items and same adapter.
The issue is that only one item is loaded under the first tab and third tab and fourth tab, While the second tab successfully loads the entire data.
I hope image added below gives better understanding regarding the issue.
Here is my adapter code
public class OthersAdapter extends RecyclerView.Adapter<OthersAdapter.OthersViewHolder> {
private final Context context;
private final ArrayList<LocalDealsDataFields> othersDataArray;
private LayoutInflater layoutInflater;
public OthersAdapter(Context context, ArrayList<LocalDealsDataFields> othersDataArray) {
this.context = context;
this.othersDataArray = othersDataArray;
if (this.context != null) {
layoutInflater = LayoutInflater.from(this.context);
}
}
class OthersViewHolder extends RecyclerView.ViewHolder implements View.OnClickListener {
TextView othersSmallTitleTextView;
ImageView othersImageView;
OthersViewHolder(View itemView) {
super(itemView);
othersSmallTitleTextView = (TextView) itemView.findViewById(R.id.others_small_title);
othersImageView = (ImageView) itemView.findViewById(R.id.others_image);
itemView.setOnClickListener(this);
}
#Override
public void onClick(View view) {
Intent couponDetailsItem = new Intent(context, LocalDealsActivity.class);
Bundle extras = new Bundle();
extras.putString(Constants.SECTION_NAME, context.getString(R.string.local_deals_section_title));
// Add the offer id to the extras. This will be used to retrieve the coupon details
// in the next activity
extras.putInt(Constants.COUPONS_OFFER_ID, othersDataArray.get(
getAdapterPosition()).getLocalDealId());
couponDetailsItem.putExtras(extras);
context.startActivity(couponDetailsItem);
}
}
#Override
public OthersViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View view = layoutInflater.inflate(R.layout.others_items, parent, false);
return new OthersViewHolder(view);
}
#Override
public void onBindViewHolder(OthersViewHolder holder, int position) {
String lfImage = othersDataArray.get(position).getLocalDealImage();
String lfCategoryName = othersDataArray.get(position).getLocalDealSecondTitle();
if (lfCategoryName != null) {
// Set the second title
holder.othersSmallTitleTextView.setText(lfCategoryName);
}
if (lfImage != null) {
if (!lfImage.isEmpty()) {
// Get the Uri
Uri lfUriImage = Uri.parse(lfImage);
// Load the Image
Picasso.with(context).load(lfUriImage).into(holder.othersImageView);
}
}
}
#Override
public int getItemCount() {
return othersDataArray.size();
}
}
I like to point out couple of things -
I've checked other answers on Stack Overflow. They talk about setting the recycler view layout_height to wrap_content. This isn't the issue as the layout_height is already wrap_content and also the second tab loads all the data as expected.
And some others answers mentioned to used same versions for all support libraries and I'm already using 25.1.0 version for all the support libraries.
Size of the data array is 20 and returning 20 from the adapter's getItemCount() method.
The data array has the expected number of items in it and they are not null or empty.
Clean build, invalidate/caches doesn't work either.
Finally, I'm using FragmentStatePagerAdapter to load the fragments when the tabs are in focus.
EDIT:
This is how I'm parsing the JSON data received
private void parseLocalDeals(String stringResponse) throws JSONException {
JSONArray localJSONArray = new JSONArray(stringResponse);
// If the array length is less than 10 then display to the end of the JSON data or else
// display 10 items.
int localArrayLength = localJSONArray.length() <= 20 ? localJSONArray.length() : 20;
for (int i = 0; i < localArrayLength; i++) {
// Initialize Temporary variables
int localProductId = 0;
String localSecondTitle = null;
String localImageUrlString = null;
JSONObject localJSONObject = localJSONArray.getJSONObject(i);
if (localJSONObject.has(JSONKeys.KEY_LOCAL_DEAL_ID)) {
localProductId = localJSONObject.getInt(JSONKeys.KEY_LOCAL_DEAL_ID);
}
if (localJSONObject.has(JSONKeys.KEY_LOCAL_DEAL_CATEGORY)) {
localSecondTitle = localJSONObject.getString(JSONKeys.KEY_LOCAL_DEAL_CATEGORY);
}
if (localJSONObject.has(JSONKeys.KEY_LOCAL_DEAL_IMAGE)) {
localImageUrlString = localJSONObject.getString(JSONKeys.KEY_LOCAL_DEAL_IMAGE);
}
if (localImageUrlString != null) {
if (!localImageUrlString.isEmpty()) {
// Remove the dots at the start of the Product Image String
while (localImageUrlString.charAt(0) == '.') {
localImageUrlString = localImageUrlString.replaceFirst(".", "");
}
// Replace the spaces in the url with %20 (useful if there is any)
localImageUrlString = localImageUrlString.replaceAll(" ", "%20");
}
}
LocalDealsDataFields localDealsData = new LocalDealsDataFields();
localDealsData.setLocalDealId(localProductId);
localDealsData.setLocalDealSecondTitle(localSecondTitle);
localDealsData.setLocalDealImage(localImageUrlString);
localDealsDataArray.add(localDealsData);
}
// Initialize the Local Deals List only once and notify the adapter that data set has changed
// from second time. If you initializeRV the localDealsRVAdapter at an early instance and only
// use the notifyDataSetChanged method here then the adapter doesn't update the data. This is
// because the adapter won't update items if the number of previously populated items is zero.
if (localDealsCount == 0) {
if (localArrayLength != 0) {
// Populate the Local Deals list
// Specify an adapter
localDealsRVAdapter = new OthersAdapter(context, localDealsDataArray);
localDealsRecyclerView.setAdapter(localDealsRVAdapter);
} else {
// localArrayLength is 0; which means there are no rv elements to show.
// So, remove the layout
contentMain.setVisibility(View.GONE);
// Show no results layout
showNoResultsIfNoData(localArrayLength);
}
} else {
// Notify the adapter that data set has changed
localDealsRVAdapter.notifyDataSetChanged();
}
// Increase the count since parsing the first set of results are returned
localDealsCount = localDealsCount + 20;
// Remove the progress bar and show the content
prcVisibility.success();
}
parseLocalDeals method is inside a helper class and it is called by using initializeHotels.initializeRV();
initializeRV() initializes the Recycler view, makes a network call to the server and the received data is passed to the parseLocalDeals method. initializeHotels being an instance variable of the Helper class.
EDIT 2:
For those who wants to explore the code in detail, I've moved the part of the code to another project and shared it on Github. Here is the link https://github.com/gSrikar/TabLayout and to understand the hierarchy check out the README file.
Can anyone tell me what I'm missing?

Not much of an answer but too long for a comment.
I have duplicated (almost) your adapter code and it fully works for me. I believe I have done the same as you. I'm using the same layout file, the same item & same adapter for all tabs. I think there are no problems with your adapter code.
I say 'almost' because I had to change a couple of things since I don't have access to your data. I changed your LocalDealsDataField model to include a BitmapDrawable & I changed onBindViewHolder() to handle it.
BitmapDrawable lfImage = othersDataArray.get(position).getLocalDealImage();
holder.othersImageView.setBackground(lfImage);
Since there seems to be no problem with your adapter, I would focus on getting the data or setting up the adapter as your problem. Sorry I can't be of help beyond that.
FYI, here's how I setup the adapter in onCreateView()
rootView = inflater.inflate(R.layout.recycler_view, container, false);
mRecyclerView = (RecyclerView) rootView.findViewById(R.id.recyclerview);
mRecyclerView.setLayoutManager(new LinearLayoutManager(getActivity()));
mAdapter = new OthersAdapter(this.getContext(), list);
mRecyclerView.setAdapter(mAdapter);

Summary
Solved the layout issue at point 1 replacing a LinearLayout by a RelativeLayout, inverting visibility logic to avoid ghost effect and catching exceptions and preventing them when the related view is not found.
Added point 2 to demonstrate that the visual defect is only present on Marshmallow and Nougat devices.
Finally FragmentStatePagerAdapter loads pages before getting focus so a fix is proposed at point 3 (load all pages and update them when are selected).
Further information in the comments below and #d4h answer.
The fourth page is not using the same layout, only the same RecyclerView and id, perhaps a work in progress. The layout issue can be solved using the same layout that previous pages but I consider this change out of scope.
1. Partially fixed for Marshmallow and Nougat devices. Work in progress.
Update2 Changing LinearLayout by RelativeLayout and inverting visibility logic solves layout issue:
Update: Commenting initializeTrending in all the fragment initializations also works onApi23+
I'll check it later, seems as deals are correctly loaded but then trending is loaded and deals are lost. WIP here.
If trending array empty and trending view gone, deals are not shown, but using invisible are shown
2. You are loading a wrong page on Marshmallow and Nougat devices
FragmentStatePagerAdapter first call to getItem() wrong on Nougat devices
This ended up having nothing to do with the FragmentStatePagerAdapter
code. Rather, in my fragment, I grabbed a stored object from an array
using the string ("id") that I passed to the fragment in init. If I
grabbed that stored object by passing in the position of the object in
the array, there was no problem. Only occurs in devices with Android 7.
FragmentStatePagerAdapter - getItem
A FragmentStatePager adapter will load the current page, and one page
either side. That is why it logs 0 and 1 at the same time. When you
switch to page 2, it will load page 3 and keep page 1 in memory. Then
when you get to page 4 it will not load anything, as 4 was loaded when
you scrolled to 3 and there is nothing beyond that. So the int that
you're being given in getItem() is NOT the page that is currently
being viewed, is the one being loaded into memory. Hope that clears
things up for you
These comments are confirmed in this branch and commit
All pages load correctly on Lollipop emulator, the last page has an extra issue, see OthersFragment:
3. Initialize all pages at creation and update them on selection.
Increase OffScreenPageLimit so all pages are initialised
Add on page selected/unselected/reselected listener
These changes solve the issue commented below:
/**
* Implement the tab layout and view pager
*/
private void useSlidingTabViewPager() {
// Create the adapter that will return a fragment for each of the three
// primary sections of the activity.
BottomSectionsPagerAdapter mBottomSectionsPagerAdapter = new BottomSectionsPagerAdapter(getChildFragmentManager());
// Set up the ViewPager with the sections adapter.
ViewPager mBottomViewPager = (ViewPager) rootView.findViewById(R.id.local_bottom_pager);
mBottomViewPager.setOffscreenPageLimit(mBottomSectionsPagerAdapter.getCount());
mBottomViewPager.setAdapter(mBottomSectionsPagerAdapter);
TabLayout tabLayout = (TabLayout) rootView.findViewById(R.id.tab_layout);
tabLayout.setupWithViewPager(mBottomViewPager);
tabLayout.addOnTabSelectedListener(new TabLayout.OnTabSelectedListener() {
/**
* Called when a tab enters the selected state.
*
* #param tab The tab that was selected
*/
#Override
public void onTabSelected(TabLayout.Tab tab) {
// TODO: update the selected page here
Log.i(LOG_TAG, "page " + tab.getPosition() + " selected.");
}
/**
* Called when a tab exits the selected state.
*
* #param tab The tab that was unselected
*/
#Override
public void onTabUnselected(TabLayout.Tab tab) {
// Do nothing
Log.i(LOG_TAG, "Page " + tab.getPosition() + " unselected and ");
}
/**
* Called when a tab that is already selected is chosen again by the user. Some applications
* may use this action to return to the top level of a category.
*
* #param tab The tab that was reselected.
*/
#Override
public void onTabReselected(TabLayout.Tab tab) {
// Do nothing
Log.i(LOG_TAG, "Page " + tab.getPosition() + " reselected.");
}
});
}
Previous Comments:
Check your LocalFragment getItem() method using breakpoints.
If you select one page, next page is also initialized, and you are sharing the recyclerView, etc.
I would move the initialization outside of getItem() as suggested here:
ViewPager is default to load the next page(Fragment) which you can't
change by setOffscreenPageLimit(0). But you can do something to hack.
You can implement onPageSelected function in Activity containing the
ViewPager. In the next Fragment(which you don't want to load), you
write a function let's say showViewContent() where you put in all
resource consuming init code and do nothing before onResume() method.
Then call showViewContent() function inside onPageSelected. Hope this
will help
Read these related questions (the first has possible workarounds to hack the limit to zero):
ViewPager.setOffscreenPageLimit(0) doesn't work as expected
Does ViewPager require a minimum of 1 offscreen pages?
Yes. If I am
reading the source code correctly, you should be getting a warning
about this in LogCat, something like:
Requested offscreen page limit 0 too small; defaulting to 1
viewPager.setOffscreenPageLimit(couponsPagerAdapter.getCount());
public void setOffscreenPageLimit(int limit) {
if (limit < DEFAULT_OFFSCREEN_PAGES) {
Log.w(TAG, "Requested offscreen page limit " + limit + " too small; defaulting to "
+ DEFAULT_OFFSCREEN_PAGES);
limit = DEFAULT_OFFSCREEN_PAGES;
}
if (limit != mOffscreenPageLimit) {
mOffscreenPageLimit = limit;
populate();
}
}

I have looked at your code, problem is same as explained by #ardock
Solution i would like to propose,
You have to change your code at 3 place ::
Inside all Fragment You are using in ViewPager Don't call initializeRESPECTIVEView() from onCreateView method.
Inside LocalFragment make a list of Fragments you are going to use with ViewPager and pass it to BottomSectionsPagerAdapter. and return Fragment from that list from getItem(int position) of BottomSectionsPagerAdapter.
Add Following code to LocalFragment inside useSlidingTabViewPager().
tabLayout.addOnTabSelectedListener(new TabLayout.OnTabSelectedListener() {
#Override
public void onTabSelected(TabLayout.Tab tab) {
}
#Override
public void onTabUnselected(TabLayout.Tab tab) {
}
#Override
public void onTabReselected(TabLayout.Tab tab) {
}
});
//Call Respective fragment initializeRESPECTIVEView() method from onTabSelected , you can get fragment instance from list you passed to BottomSectionsPagerAdapter

Swipe tabs for unknown amount of items

I will try to explain what I am thinking of doing as an Android app. But I am really confused how would I approach this problem.
When you get JSON from some web API (eg Location) and let's say that JSON has 5 different locations and you want to store each Location as a separate list item in a list view. This is simple, you use a location adapter class, and then those 5 items get stored as a list. For example, JSON updates 24h later and now there are 10 locations. No problems at all - Android handles this because of location adapter and etc. (I know all of this). Basically, what I am trying to tell that android does not need to know how many list items there will be before fetching information from JSON.
Now, the problem is that I am trying to create a swipe views which will represent each of the list items (1 Full view = 1 list item). For example, if there are 5 locations, i can only swipe 4 times and then I will reach the last tab. If there is update, and there are 10 locations, I could only swipe 9 times until I reach the end. I hope you understand idea.
My question is - how do I create dynamic swipe views where each of the list items would have its own separate window and to reach another list item you would swipe?
My main concern is how do you not tell android how many swipe views you will need and he would figure it out when he reads the JSON and knows the number of locations.
Many Thanks

Let's say your data is like this:
{"India","Morocco","China","Russia"}
You can getLength of the JSON object.In this case it is 4.Save that in a static variable.Suppose
max_swipes=4
Then in you swipe method
`if(position<=max_swipes || position==0){//code to swipe }
else
{
//cannot swipe last position
}`

To implement such functionality you just simply can use viewPager. You can copy the code from here and here. These are two file and you just need to copy as it is. After adding these two files in your project you need to create an adapter and here is the thing which makes it dynamic to create swipe views.
I am adding code snippet hope it will help you.
public class ViewPagerAdapter extends FragmentStatePagerAdapter {
private DetailFragment page;
CharSequence Titles[]; // This will Store the Titles of the Tabs which are Going to be passed when ViewPagerAdapter is created
int NumbOfTabs; // Store the number of tabs, this will also be passed when the ViewPagerAdapter is created
// Build a Constructor and assign the passed Values to appropriate values in the class
public ViewPagerAdapter(FragmentManager fm, CharSequence mTitles[], int mNumbOfTabsumb) {
super(fm);
this.Titles = mTitles;
this.NumbOfTabs = mNumbOfTabsumb;
}
//This method return the fragment for the every position in the View Pager, This method is called only when we slide or change the tabs and not called upon rotating the screen
#Override
public Fragment getItem(int position) {
if(position < NumbOfTabs)
{
page= new DetailFragment();
return page;
}else {
return null;
}
}
// This method return the titles for the Tabs in the Tab Strip(in case you want to add title to each page.
#Override
public CharSequence getPageTitle(int position) {
return Titles[position];
}
#Override
public int getCount() {
return NumbOfTabs;
}
}
While creating the instance of this adapter you can pass the number of page you are going to require by calculating the number of items in JSON.
Hope this will help.

Android - ViewPager Adapter, set primary item before adapter is instantiated

I know i can do
viewPager.setCurrentItem(position)
to set my view pager at the desired position. My question is if and how i can do this before the adapter is instantiated.
Meaning that if I do
pagerAdapter = new ViewPagerAdapter(arg1,arg2....);
viewPager.setAdapter(pagerAdapter);
viewPager.setCurrentItem(position);
item 0 is first build and after that the item at the desired position is also build. Which takes double the time...In my adapter each item needs quite a lot of work to be build, so it would be best to avoid the 0 position item to be build if possible. Maybe by passing the desired position as an argument at the adapter's instantiation...?
Any way to do that?

If the time and work is what you're worry about, I'd try to avoid building the page at position 0 until the desired one has been built. You could use a variable lets say "desiredPageHasBeenBuilt" in your adapter, when requesting the item at position 0 you could return an "empty page" if the variable desiredPageHasBeenBuilt is false, when your desired page has been build set the variable to true and the page 0 can be built.

For a solution that works in Android M as well as older versions, use reflection as follows:
int currentItem = 5;
// Set initial position first...
Field field = ViewPager.class.getDeclaredField("mRestoredCurItem");
field.setAccessible(true);
field.set(mPager, currentItem);
// ...and then set adapter
mPager.setAdapter(adapter);
Using reflection is safe, because you control the ViewPager implementation (it's included with your app).
If you use Proguard, then you need to include the following in its config:
-keepclassmembers class android.support.v4.view.ViewPager {
private int mRestoredCurItem;
}
or the field mRestoredCurItem will be renamed by Proguard.

You can just set blank adapter and after that set your real adapter this way you will "trick" the viewpager and you want load any data you dont want to.
this.viewPager.setAdapter(new PagerAdapter() {
#Override
public int getCount() {
return 0;
}
#Override
public boolean isViewFromObject(View view, Object object) {
return false;
}
});
this.viewPager.setCurrentItem(imagePosition, false);
this.viewPager.setAdapter(adapter);
this.viewPager.setCurrentItem(imagePosition, false);

You can fool the viewpager to start at a given position before the adapter is set, by calling onRestoreInstanceState, like this:
int currentItem = 5;
Parcel parcel = Parcel.obtain();
writeParcelable(BaseSavedState.EMPTY_STATE, 0);
writeInt(currentItem);
writeParcelable(null, 0);
setDataPosition(0);
SavedState savedState = ViewPager.SavedState.CREATOR.createFromParcel(parcel);
mPager.onRestoreInstanceState(savedState);
mPager.setAdapter(mAdapter);

Maybe this is not the answer you're looking for, but have you tried to it as it was designed? Do not start heavy work on page fragment before it is attached to the screen. That way you'll get that behavior you want without hacking android implementation.

you can do this trick:
refactor all of your heavy work into a function, because creating a fragment is not takes much time, and only execute the function when user is going to see it by calling that function inside OnPageChangeListener listener and at the
#Override
public void onPageSelected(int position){
// call your function that do heavy working
}

ViewPager - update view after adapter got empty

I'm using a FragmentStatePagerAdapter with a ViewPager.
Everything is working fine. If I open my activity with an empty Adapter, the ViewPageris empty, if I add items, the ViewPager updates correctly.
BUT, if I open my activity and delete the last item of my ViewPager, the ViewPagerdoes not invalidate correctly and keeps the last Fragment visible.
How can I avoid this?
I'm using my library, it's a wrapper class for ViewPager + ViewPagerIndicator + FragmentPager(State)Adapter:
The class itself is placed here: https://github.com/MichaelFlisar/PagerManager/blob/master/src/com/michaelflisar/pagermanager/MFragmentPagerStateAdapter.java
The implementation is placed here: https://github.com/MichaelFlisar/PagerManager/blob/master/src/com/michaelflisar/pagermanager/MPagerAdapterHelper.java
It implements a simple FragmentStatePagerAdapter with weak references to it's fragments...
My code looks like following:
mPagerManager = new MPagerManager<ExerciseViewFragment, MFragmentPagerStateAdapter<ExerciseViewFragment>>(pager, tpi,
new MFragmentPagerStateAdapter<ExerciseViewFragment>(fragmentManager)
{
#Override
public CharSequence getPageTitle(int pos)
{
return mData.workout.getWExercise().get(pos).getExercise().getName();
}
#Override
public int getCount()
{
return mData.workout.getWExercise().size();
}
#Override
public ExerciseViewFragment createFragment(int pos)
{
return ExerciseViewFragment.newInstance(pos, mData.workout.getWExercise());
}
});
I'm calling mPagerManager.notifyDataSetChanged(); which forwards the call to the FragmentPagerStateAdapter directly...
PS: I know, I can make it invisible, if item count is 0... But I'm wondering if there's a better solution

This is an old question but I thought you might still need to know what to do. It's very common issue. ViewPager does not invalid views which are already created(including these which are ready on the left and right side of your current view).
Solving this is very easy. Just implement the following method in your adapter like this:
#Override
public int getItemPosition(Object object) {
return POSITION_NONE;
}
By default this method returns PagerAdapter.POSITION_UNCHANGED.
For most developers this method usage is misleading, I had this problem myself till I realised that this method is used by ViewPager.dataSetChanged() to establish which items should be recreated. With above code you tell ViewPager to recreate all items whenever data set change.

multiple Fragments with different expandableList's for same data

this question might be very noobish but I'm just not able to find a right solution.
So here is my problem:
I want do display the data (a java.util.List with my TaskObjects) in multiple ExpandableLists (lets say 5) each in a own Fragment so that the user is able to swipe between the different Lists.
At the moment I have a MainFragmentActivity that contains the java.util.List, the PageViewer and a 'extended' FragmentPagerAdapter (like TabsAdapter) that contains the Tabs AllTaskFragment and OverDueTaskFragment. These two Fragments have each a own ExpandableList and ExpandableListAdapter (writen by me).
Now when the user clicks on a child in any ExpandableLists how do i need to notify the other Fragments ExpandableListAdapter to update? I tried to call the MainFragmentActivity and from there call all Fragments but then the fragments ExpandableListAdapters were 'null', but why?
update:
I guess I solved the issue, atm Is working with:
If something changes in any ExpandableListAdapter, I call updateTabs() in
MainFragmentActivity
public void updateTabs() {
for(int i = 0 ; i < tabsAdapter.getCount() ; i++) {
UpdateableFragment updateableFragment = (UpdateableFragment) getSupportFragmentManager().findFragmentByTag(makeFragmentName(mViewPager.getId(),i));
updateableFragment.updateFragment();
}
}
private String makeFragmentName(int viewId, int index){
return "android:switcher:" + viewId + ":" + index;
}
which simply calls in each fragment the method
public void updateFragment() {
adapter.notifyDataSetChanged();
}
Is this a good approach? Or will this maybe rise some issues?

The key thing for such applications is to keep track of the ArrayAdapters. If you call ArrayAdapter.notifyDataSetChanged(), it will tell its view to update.