Develop Reference

Android pagination boundary callback clarification

I've integrated the pagination component in my app and it's working perfectly fine (almost).
I've Database + network model. Database initially has some items which are consumed by LivePagedListBuilder. I observe this LiveData<PagedList<InboxEntity>> and ultimately feed the list to PagedListAdapter#submitList(PagedList<T> pagedList), something like :
LiveData<PagedList<Entity>> entities;
PagedList.Config pagedListConfig =
(new PagedList.Config.Builder()).setEnablePlaceholders(true)
.setPrefetchDistance(5)
.setEnablePlaceholders(false)
.setPageSize(10)
.setInitialLoadSizeHint(10)
.build();
entities = new LivePagedListBuilder<>(DAO.getItemList(), pagedListConfig)
entities.observe(this, new Observer<PagedList<Entity>>() {
#Override
public void onChanged(#Nullable PagedList<Entity> inboxEntities) {
inboxAdapter.submitList(inboxEntities);
isFirstLoad = false;
}
});
DAO#getItemList returns DataSource.Factory<Integer, Entity>.
I am listening for the boundary callback and trigger a network call when it reaches the end of the paged list. That call populates the database again.
There's one more thing. I've registered AdapterDataObserver on recycler view because if an item has been inserted at the beginning, I've to scroll to the top position:
RecyclerView.AdapterDataObserver adapterDataObserver = new RecyclerView.AdapterDataObserver() {
#Override
public void onItemRangeInserted(int positionStart, int itemCount) {
if (positionStart == 0) {
layoutManager.scrollToPositionWithOffset(positionStart, 0);
}
}
};
I am facing a problem in this model :
After making the network call, database is populated again and onChanged function is called with a new PagedList<Entity>. Now, does this paged list contains only the new items. I've confirmed this.
But onItemRangeInserted method is called with positionStart as 0 too, which suggests that items are being inserted at the beginning. But they are not. They are being inserted at the end, confirmed with stetho db inspector.
Then why is the onItemRangeInserted being called with positionStart as 0? This is making it difficult for me to distinguish when a fresh item is inserted at the beginning of the adapter and when items are inserted at the end.
Edit:
value of itemCount is 10 which is my page size.
In DiffCallback, I just compare the primary key column of the two entities in areItemsTheSame function.

This is how I'm doing it, not ideal but it works. I'm using a recycler view with reverse set to true as it's a chat app so you'll have to adjust for your use case.
In your fragment create a Timer field:
private Timer mTimer;
Add a scroll state listener that sets a "latest row id" that you can compare later.
mRecyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {
#Override
public void onScrollStateChanged(#NonNull RecyclerView recyclerView, int newState) {
super.onScrollStateChanged(recyclerView, newState);
if (newState == RecyclerView.SCROLL_STATE_DRAGGING) {
//Get the latest id when we started scrolling
AppExecutors.getInstance().databaseIO().execute(() ->
mLatestMessageId = mHomeViewModel.getMessageViewModel().getLatestMessageId(mOurUsername, mChatname));
}
}});
Use the AdapterDataObserver to kick off a new timer when the insert is called.
private RecyclerView.AdapterDataObserver mAdapterDataObserver = new RecyclerView.AdapterDataObserver() {
#Override
public void onItemRangeInserted(int positionStart, int itemCount) {
if (mTimer != null) {
mTimer.cancel();
}
mTimer = new Timer();
mTimer.schedule(new CheckNewMessageTimer(), 100);
}
};
Here's the timer class, if new items have been inserted the "latest row id" will have incremented in the database. I'm only scrolling to the bottom if I'm already at the bottom, otherwise I just change the color of a "scroll to bottom" FAB that I have.
class CheckNewMessageTimer extends TimerTask {
#Override
public void run() {
if (newItemsAdded()) {
int firstItemPosition = mLinearLayoutManager.findFirstVisibleItemPosition();
boolean atBottom = firstItemPosition == 1;
SurespotLog.d(TAG, "CheckNewMessageTimer, firstItemPosition: %d, atBottom: %b", firstItemPosition, atBottom);
AppExecutors.getInstance().mainThread().execute(() -> {
if (atBottom) {
SurespotLog.d(TAG, "CheckNewMessageTimer, scrolling to bottom");
mListView.scrollToPosition(0);
}
else {
if (mFab != null) {
SurespotLog.d(TAG, "CheckNewMessageTimer, new message received but we're not scrolled to the bottom, turn the scroll button blue");
mFab.setBackgroundTintList(ColorStateList.valueOf(getResources().getColor(R.color.surespotBlue)));
}
}
});
}
}
private boolean newItemsAdded() {
int dbLatestMessageID = mHomeViewModel.getMessageViewModel().getLatestMessageId(mOurUsername, mChatname);
if (mLatestMessageId > 0 && dbLatestMessageID > mLatestMessageId) {
mLatestMessageId = dbLatestMessageID;
return true;
}
return false;
}
}

Android Spinner How to not show specific selections

I have a spinner in a toolbar, I also have replaced the toolbar with an icon and when the user selects the first option and the last option in the spinner I do not want it to show, or in other words do not want to replace the Spinner with text but the rest for the rest between the first and last option. I want them to show. How can I do this?
public void onItemSelected(AdapterView<?> adapterView,
View view, int i, long l) {
int total = adapterView.getCount();
if(i == 0){
}
else if(i == total -1){
}

// declare it inside class
private int prev_pos=0; // initially it zero, you can set your desire position
if(i =! 0 && i!= adapterView.getCount()-1 )
{
// do what you want
prev_pos=i; // store the previous position if it's not last or first
}
else{
// display previous position
yourSpinnerObject.setSelection(prev_pos);
}

listview - access to non-visible items

I would like to check which of elements on my listview is also a member of another list and check all of them (by changing background). But the only way I can think of is:
for (String str : list1){
if (list2.contains(str)) {
lv.getChildAt(adapter.getPosition(str)).setBackgroundColor(getResources().getColor(android.R.color.darker_gray));
}
}
But that works only for visible elements of the list and throws null pointer exception when accessing non-visible elements. What can I do to apply changes for all list items? Do I have to write my own adapter or maybe there is any "equivalent" of getChiledAt but working for all elements of the listview not only visible ones?

I didn't try by myself, but a suggestion. Can you please try this way, and check.
Idea is to use setOnScrollListener with onScroll method and to have null check inside for loop.
It's not good solution though, because for loop working on every scroll.
lv.setOnScrollListener(new OnScrollListener() {
#Override
public void onScrollStateChanged(AbsListView arg0, int arg1) {
// TODO Auto-generated method stub
}
#Override
public void onScroll(AbsListView arg0, int arg1, int arg2, int arg3) {
// TODO Auto-generated method stub
for (String str : list1) {
if (list2.contains(str)) {
if (lv.getChildAt(adapter.getPosition(str)) != null) {
lv.getChildAt(adapter.getPosition(str))
.setBackgroundColor(
getResources()
.getColor(
android.R.color.darker_gray));
}
}
}
}
});

The solution was to use onScroll method (as Chitrang suggested) and set everything only for visible item. Android Magic works, everything works fine, also for non-visible items :)
#Override
public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
for (int i = lv.getFirstVisiblePosition(); i<=lv.getLastVisiblePosition(); i++){
if (list2.contains(lv.getItemAtPosition(i).toString()))
lv.getChildAt(i - lv.getFirstVisiblePosition()).setBackgroundColor(getResources().getColor(android.R.color.darker_gray));
}
}
}

You can create a new List, with the (i assume you have) id like the listview's data.
Example :
You have class Person with int id, String name. Create a new List<Integer> to store all (not just the visible one) of your listview's person id, normally by using the listview's adapter.

Scroll a ListView to the top without any screen flickering

I have implemented a ListView that has the functionality that you see in many apps, where user scrolls to bottom and it loads more, that OnScrollListener is this:
public class OnScrolledToEndListener implements AbsListView.OnScrollListener
{
private int prevLast;
#Override
public void onScrollStateChanged(AbsListView absListView, int i)
{
}
#Override
public void onScroll(AbsListView absListView, int first, int visible, int total)
{
int last = first + visible;
if (last == total)
{
if (prevLast != last)
{
prevLast = last;
onScrolledToEnd();
}
}
}
public void onScrolledToEnd()
{
}
}
Now the problem is that when a user has scrolled to the bottom of a list, and hits the refresh button in my app, I want it to start over at the top of the list, because if it stays at the bottom of the list, then the scroll listener will immediately trigger. The best way I've found to solve this is by doing the following before executing the refresh:
mListView.setSelection(0);
mListView.post(
new Runnable()
{
#Override
public void run()
{
mListView.setVisibility(View.GONE);
mLoadingLayout.setVisibility(View.VISIBLE); //this is basically a progressbar
// do the refresh
}
}
);
But there is a slight flicker when the list scrolls to the top. Any ideas on how to make it look better?

I figured out the solution. Apparently setting the ListView to View.GONE makes it not update its layout, so I set it to View.INVISIBLE instead and it worked. I didn't even have to use a Runnable.
mListView.setSelection(0);
mListView.setVisibility(View.INVISIBLE);
mLoadingLayout.setVisibility(View.VISIBLE);

On scroll change using list-view Android

I am developing an application which consists on scroll-change-listener,Here is my problem, I am getting the Number of items for the server.Until here every thing works fine to me.
1.IF i am showing the 10 values in the list-view,that 10 values only should stream.
2.When Scroll state is changed the reaming item should hit server.
3.Below is my code .
#Override
public void onScroll(AbsListView view, int firstVisibleItem,int visibleItemCount, int totalItemCount) {
if (visibleItemCount < 1)
return;
streaming.clear();
int firstPoisitionValue = symbolList.getFirstVisiblePosition();
int lastPositionValue = symbolList.getLastVisiblePosition();
WatchListData row;
String symbol;
for (int i = firstPoisitionValue; i <= lastPositionValue; i++) {
row = model.get(i);
symbol=row.getSymbol();
Log.w("Hello Android", "Symbol Value ::>"+symbol);
streaming.add(symbol);
}
if (streamFlag) {
System.out.println("calling the request");
streamingRequest("quote", streamingSymbols);
streamFlag = false;
}
}
#Override
public void onScrollStateChanged(AbsListView view, int scrollState) {
pauseStreaming();
if(scrollState == SCROLL_STATE_IDLE){
streamingRequest("quote", streamingSymbols);
}
Thanks,
Nikhilreddy.

You can do this by using onScroll Listener. Using this listener When scroll reaches the end you can load new items to the list. refer this link. It may help you.Dynamic listView