In my app I use a ViewPager in conjunction with PageTransformer to display some data list as a card deck. That list is sometimes refreshed and it contains plenty of items in a common case, so I use FragmentStatePagerAdapter with needed page limit:
public class PlaceListPagerAdapter extends FragmentStatePagerAdapter {
private List<PlaceListData> items;
public PlaceListPagerAdapter (FragmentManager manager) {
super (manager);
items = new ArrayList<>();
}
#Override
public Fragment getItem(int position) {
String id = items.get(position).getId();
String name = items.get(position).getName();
String address = items.get(position).getAddress();
return PlaceFragment.newInstance(id, name, address);
}
#Override
public int getCount() {
return items.size();
}
#Override
public int getItemPosition(Object object) {
PlaceFragment frag = (PlaceFragment) object;
String id = frag.getDataId();
for (PlaceListData data : items) {
if (id != null && id.equals(data.getId())) {
return POSITION_UNCHANGED;
}
}
return POSITION_NONE;
}
public void addItems(List<PlaceListData> items) {
this.items.addAll(items);
notifyDataSetChanged();
}
public void replaceItems(List<PlaceListData> items) {
this.items.clear();
addItems(items);
}
public void clearItems () {
this.items.clear();
notifyDataSetChanged();
}
}
Nothing unusual - list of pojos, overriden getItemPosition() and add/clear methods with notifyDataSetChanged(). The problem is when I try to add/replace items over network, method transformPage(View view, float position) of my transformer is called with 0.0 position for all new views and they are placed one over another (transformation is broken).
After debugging ViewPager class I noticed that transformPage(View view, float position) is invoked only in one place in onPageScrolled(..) method of ViewPager and the latter is invoked in onLayout(..) after the first layout pass.
notifyDataSetChanged() invokes onPageScrolled(..) (and transformPage(View view, float position) respectively) and requestLayout() after that. The problem is that first invocation of transformPage(View view, float position) happens before layout pass and position parameter depends on View.left() which returns 0 as child views are not layouted. In onLayout(..) which follows the requestLayout() my transformPage(View view, float position) is not called at all because yeap, views are layouted now, but it is not the first layout pass.
The problem is cured by resetting adapter (it sets mFirstLayout flag in ViewPager to "true") or by calling any public method of ViewPager which invokes transformPage(View view, float position) in it's code such as scrollTo, fakeDrag etc, but I'd like to know - is all that a feature of ViewPager or is it a bug or am I doing something very very wrong?
Sorry for my bad English and thanks in advance!
Related
I have a gallery/slideshow activity that allows user to swipe between Photos. Each "Page" is just a TouchImageView. There is a pagination logic in there, and I can see that it is calling the API accordingly. However, I am not able to swipe further even after notifyDataSetChanged has been called. Here's the code:
Activity {
ViewPager vp;
CustomPagerAdapter pagerAdapter;
onCreate() {
//api callback
pagerAdapter = new CustomPagerAdapter();
vp.setAdapter(pagerAdapter);
}
}
CustomPagerAdapter() {
TouchImageView imageView;
List<Photos> photos;
int getCount() {
return photos == null ? 0 : photos.size();
}
#Override
public boolean isViewFromObject(View view, Object object) {
return view == object;
}
#Override
public Object instantiateItem(ViewGroup container, int position) {
View itemView = mLayoutInflater.inflate(R.layout.pager_image, container, false);
imageView = (TouchImageView) itemView.findViewById(R.id.photo);
Glide.with(context)
.load(photos.get(position).getUrl())
.into(imageView);
container.addView(itemView);
if (position == photos.size()-1) {
loadMorePhotos();
}
return itemView;
}
#Override
public int getItemPosition(Object object) {
return POSITION_NONE;
}
#Override
public void destroyItem(ViewGroup container, int position, Object object) {
container.removeView((RelativeLayout) object);
}
void loadMorePhotos() {
//call api and stuff
void onResponse(Call call, Response<List<Photo>> response) {
photos.addAll(response.body);
notifyDataSetChanged();
}
}
}
And this is the result:
http://imgur.com/nA1TzfI
I have no idea what is going on for 2 days. Please help!
This may not be ideal, but where you call notifyDatasetChanged() you could instead try calling vp.setAdapter(pagerAdapter);
(i.e. actually re-set the adapter). A downside of this is that the pager will probably go back to having the first page selected. To avoid this, you'd need to save the latest page somewhere and restore it afterwards.
As I say, not ideal, but it may help.
You dont have to load more photos from adapter class, in your activity class you can use onPageScrolled and call the api when the last item is scrolled and set adapter again also save state of view pager before calling api to retain it when adapter is set again.
private boolean isLastPageSwiped;
private int counterPageScroll;
private OnPageChangeListener mListener = new OnPageChangeListener() {
#Override
public void onPageSelected(int arg0) {
// TODO Auto-generated method stub
}
#Override
public void onPageScrolled(int arg0, float arg1, int arg2) {
// TODO Auto-generated method stub
if (position == 6 && positionOffset == 0 && !isLastPageSwiped){
if(counterPageScroll != 0){
isLastPageSwiped=true;
//call api
}
counterPageScroll++;
}else{
counterPageScroll=0;
}
}
#Override
public void onPageScrollStateChanged(int arg0) {
// TODO Auto-generated method stub
}
};
and use this listener
vp.setOnPageChangeListener(mListener);
We can use this approach for doing pagination on ViewPager (with fragment)
load new page data but not append to the adapter
make sure the page is not scrolling, then append new page data into the adapter (ViewPager.OnPageChangeListener#onPageScrolled's positionOffsetPixels == 0).
update current item for view pager with offset = new page data's size (let's call it newPosition)
rebind data to 3 fragments: newPosition - 1, newPosition, newPosition + 1
For getting current fragment, we can use fragment manager
private fun getFragment(position: Int): PageFragment? =
supportFragmentManager.fragments.firstOrNull {
(it as? PageFragment)?.position == position // always pass possition value into the fragment
} as? PageFragment
We need to append data when not scrolling (step 2) to have a better UX to users. If we append data immediately when it comes and if user is scrolling, view pager's setCurrentItem will make a strange move.
I create a simple version here https://github.com/tuanchauict/DemoPaginationViewPager. Please take a look
I am calling an api that returns json. I parse the json into an arraylist of objects. I have a class that i created to randomly select an element from the list and remove it and display it in the viewpager. I have the viewpager and pageradapter set up and asyncloader to create the dataset. I get a runtime exception with the following. If i change the getCount() to return a static number then it works as i want it to but it doesnt accomplish my requirements that i listed below.
The application's PagerAdapter changed the adapter's contents without calling PagerAdapter#notifyDataSetChanged! Expected adapter item count: 14, found: 12 Pager id
I totally understand why it is happening. The following code is why.
random element class: this method provides the random object i want to display in the viewpager at the same time removing from the list so i do not retrieve it again.
public T spin() throws IllegalStateException, NullPointerException {
if (list == null)
throw new NullPointerException("A list has not been set.");
if (list.size() > 0) {
int i = rand.nextInt(list.size());
T b = list.remove(i);
return b;
} else {
throw new IllegalStateException("There are no more elements left. Please query more.") ;
}
}
This is my inner pageradapter class - r is the object of the randomelement class:
private class RPagerAdapter extends PagerAdapter {
private Context context;
public RPagerAdapter(Context context) {
this.context = context;
}
#Override
public int getCount() {
return r.size();
}
#Override
public void destroyItem(ViewGroup container, int position, Object object) {
container.removeView((View) object);
}
#Override
public Object instantiateItem(ViewGroup container, int position) {
ViewHolder mViewHolder = new ViewHolder(context);
mViewHolder.setItem(r.spin());
container.addView(mViewHolder);
return mViewHolder;
}
#Override
public boolean isViewFromObject(View view, Object object) {
return view == object;
}
}
What im trying to accomplish is the following:
The user can only swipe forward (to the left) thus the spin method will be invoked correctly. (priority)
When the the spin method returns an exception the loader is called to load more data. (not a priority right now)
The user cannot be allowed to swipe right because the functionality of the app is for the user to only see a random element once (which the randomelement class accomplishes) so i need the viewpager to understand to only move in one direction meaning a new random element is displayed.
Please let me know if there is a different way that i can implement the above or point me in the right android apis to use.
A call to the PagerAdapter method startUpdate(ViewGroup) indicates
that the contents of the ViewPager are about to change. One or more
calls to instantiateItem(ViewGroup, int) and/or destroyItem(ViewGroup,
int, Object) will follow, and the end of an update will be signaled by
a call to finishUpdate(ViewGroup).
Therefore, you should only perform your update in the list in finishUpdate(ViewGroup)
forget about your whole spin structure, try something like this, pseudo code only:
private class RPagerAdapter extends PagerAdapter {
private Context context;
private List<T> items;
public RPagerAdapter(Context context, List<T> items) {
this.context = context;
this.items = items;
}
#Override
public int getCount() {
return items.size();
}
#Override
public void destroyItem(ViewGroup container, int position, Object object) {
container.removeView((View) object);
}
#Override
public Object instantiateItem(ViewGroup container, int position) {
ViewHolder mViewHolder = new ViewHolder(context);
mViewHolder.setItem(items.get(position));
container.addView(mViewHolder);
container.setTag(String.valueOf(position));
return mViewHolder;
}
#Override
public void finishUpdate(ViewGroup container) {
int position = Integer.parseInt(container.getTag());
//remove all items before position
//add items at the end if you want
notifyDataSetChanged();
viewPager.setCurrentItem(0, false);
}
#Override
public boolean isViewFromObject(View view, Object object) {
return view == object;
}
}
I am trying to implement a ViewPager without using Fragments. Let's say, I have an unspecific amount of data stored inside some kind of database which is mapped to specific days. What I am trying to do is to display the data for a specific day on ViewPager pages.
This is what I am currently doing:
#Override
protected void onCreate(Bundle savedInstanceState) {
dataList = (ViewPager) findViewById(R.id.dataList);
dataList.setAdapter(new DataListSlidePagerAdapter());
dataList.setCurrentItem(Integer.MAX_VALUE / 2);
}
private class DataListSlidePagerAdapter extends PagerAdapter {
int lastPosition;
#Override
public Object instantiateItem(ViewGroup collection, int position) {
if (position > lastPosition) {
GregorianCalendar today = Settings.getCurrentDay();
today.add(GregorianCalendar.DATE, 1);
Settings.loadData();
}
else if (position < lastPosition) {
GregorianCalendar today = Settings.getCurrentDay();
today.add(GregorianCalendar.DATE, -1);
Settings.loadData();
}
lastPosition = position;
LinearLayout v = createDataList(Settings.getTodaysData());
collection.addView(v);
return v;
}
#Override
public void destroyItem(ViewGroup collection, int position, Object view) {
((ViewPager) collection).removeView((LinearLayout) view);
}
#Override
public int getCount() {
return Integer.MAX_VALUE;
}
#Override
public boolean isViewFromObject(View arg0, Object arg1) {
return arg0 == ((View) arg1);
}
public int getItemPosition(Object object) {
return POSITION_NONE;
}
}
This actually almost works, but unfortunately, the data for the current day is never shown on the current page, but rather on the next or previous page. My guess would be, that this is because instantiateItem does not necessarily build the view of the current page, but rather of some page which is probably needed to be shown next. createListData(), however, always creates the view of the current day.
Any idea how to fix this and to display the right data on the right pages? You can assume, that there are also functions like Settings.getTomorrowsData() and Settings.getYesterdaysData().
I would like to keep a list of 3 views at all times. The app starts at position 1 (out of positions 0,1,2). When someone scrolls to position 0, I would like to remove view 2, and create a view before position 0. This way, it appears to the user, that there are unlimited views. In the same way, when someone scrolls to position 2, I would like to remove the view at position 0 and add one at the end.
However I'm having problems with both adding and removing views. When I get to position 0, nothing changes unless I try scrolling past position 0 (to position -1, i.e. the boundary is hit). At that point, I can see that it is the boundary of my views, but then setCurrentItem(1,false) is triggered and I'm brought back to the middle of the views. When I scroll to position 2 I see that position 2 has been updated. However position 0 and 1 remain the same.
When I scroll to position 2, nothing happens. However if I try and scroll to the boundary, for some reason, position 0 gets updated and setCurrentItem(1,false) is triggered.
I have no idea why its happening like this. Can anyone shed some light on this?
Here is my code:
public class MainActivity extends Activity {
ArrayList<Integer> showThree = new ArrayList<Integer>();
int focusedPage = 0;
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
showThree.add(0,5); //adding integers 5,6,7 for positions 0,1,2
showThree.add(1,6);
showThree.add(2,7);
final MyPagerAdapter adapter = new MyPagerAdapter(getApplicationContext(),showThree);
final ViewPager myPager = (ViewPager) findViewById(R.id.mypanelpager);
myPager.setAdapter(adapter);
myPager.setCurrentItem(1);
myPager.setOnPageChangeListener(new OnPageChangeListener(){
#Override
public void onPageScrollStateChanged(int state) {
if (state == ViewPager.SCROLL_STATE_IDLE) {
//when position= 0, change the 3 views from 5,6,7 to 4,5,6.
if (focusedPage == 0) {
showThreeMonths.set(0,4);
showThreeMonths.set(1,5);
showThreeMonths.set(2,6);
adapter.notifyDataSetChanged();
adapter.startUpdate(myPager);
}
else if (focusedPage ==2){
//ignore, just testing focusPage=0 for now }
}
//set current page to the middle of the 3 new views, which would be
//the same view at position 0 of the old 3 views.
//Thus user doesn't experience the views changing despite being 3 new views.
myPager.setCurrentItem(1,false);
}
#Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
// TODO Auto-generated method stub
}
#Override
public void onPageSelected(int position) {
focusedPage = position;
}
});
}
PagerAdapter
public class MyPagerAdapter extends PagerAdapter {
private ArrayList<Integer> showThreeMonths;
private Context ctx;
public MyPagerAdapter (Context ctx, ArrayList<Integer> showThree){
this.ctx = ctx ;
this.showThree = showThree;
}
#Override
public int getCount() {
return showThree.size();
}
public Object instantiateItem(ViewGroup collection, int position ){
//NewCustomView is a class I made that takes parameters context and an integer and creates a view based on the integer
NewCustomView MyOwnView = new NewCustomView(ctx, showThree.get(position));
View customViewLayout = MyOwnView.newLayout; //part of the class object
collection.addView(customViewLayout);
return customViewLayout;
}
#Override
public void destroyItem(ViewGroup collection, int position, Object arg2) {
((ViewPager) collection).removeView((ViewGroup) arg2);}
#Override
public Parcelable saveState() {
return null;}
#Override
public boolean isViewFromObject(View view, Object arg1) {
return view==arg1;}
#Override
public void startUpdate(ViewGroup collection) {}
#Override
public void finishUpdate(ViewGroup collection) {}
}
The instantiateItem() method creates the 2 view pages in the memory by default. Therefore when you swipe to the second page then 0 page is recreated as it's outside the range of the 2 pages saved in the memory. Please try to use
myViewPager.setOffscreenPageLimit(numberOfPages)
method that receives an integer as a parameter and declares how many pages it should be keeping before recycling them.
I want to get the current position of the visible view of my PagerAdapter
I didn't see an obvious function like getPosition() and I want one.
I want to add an object into its arraylist at that position, but I need to know it first
You would use:
int position = mViewPager.getCurrentItem()
I had this problem and could not get the getCurrentItem() methode.
I ended up getting the position from the ViewPager and not from the PageAdapter. The onPageSelected(int currentPage) methode is getting the currently displayed page.
//custom PageAdapter implementation
mAdapter = new AwesomePagerAdapter();
//Our custom view pager that extends from ViewPager
mPager = (CustomViewPager) findViewById(R.id.preview_gallery);
mPager.setAdapter(mAdapter);
// get the item that we should be showing from the intent
mCurrentPage = extra.getInt("currentIndex");
// show the item the user picked
mPager.setCurrentItem(mCurrentPage);
// listen for page changes so we can track the current index
mPager.setOnPageChangeListener(new OnPageChangeListener() {
public void onPageScrollStateChanged(int arg0) {
}
public void onPageScrolled(int arg0, float arg1, int arg2) {
}
public void onPageSelected(int currentPage) {
//currentPage is the position that is currently displayed.
}
});
Doing it in the PageAdaper didn't work for me as I want to preload images that are not visible. The position that is passed instantiateItem(View collection, int position) of the PageAdapter` is the position of the next item initialized. This has nothing to do with the item that is displayed.
https://github.com/Shereef/ViewPagerPlusExpandableList/blob/master/src/net/shereef/vewpagerplusexpandablelistexample/ViewPagerPlusExpandableListActivity.java#L204
if i write after that line
Log.i("pager",myPager.getCurrentItem()+"");
it will show in the logcat the current item page while the oncreate is being run which is always 0
noteice i have used the object for the viewpager it self not the adapter.
Here's an updated solution that I used myself. Since setOnPageChangeListener is now deprecated you must use addOnPageChangeListener.
viewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
#Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
int counterPosition;
if (position == 0 || position <= currentInventory.size()){
counterPosition = position + 1;
} else {
counterPosition = position;
}
viewPagerHeader.setText("Prize " + counterPosition + " of " + currentInventory.size());
}
#Override
public void onPageSelected(int position) {
}
#Override
public void onPageScrollStateChanged(int state) {
}
});
The implementation above displays the correct index in my TextView so that positions 0 and the last item in the listcurrentInventory.size() display correctly.
Hope this helps someone looking for an updated solution.
Try this:
imageSlider.addOnPageChangeListener(object: ViewPager.OnPageChangeListener{
override fun onPageScrolled(position: Int, positionOffset: Float, positionOffsetPixels: Int) {}
override fun onPageSelected(position: Int) {Log.d(TAG, "Page No.: $position")}
override fun onPageScrollStateChanged(state: Int) {}
})
I just faced this problem yesterday. I needed to start playing an animation in each page when the page is visible to the user and not before.
My adapter inherits from PagerAdapter and I found out that there is a function setPrimaryItem() which is triggered every time a page is shown to the user as the current page.
Called to inform the adapter of which item is currently considered to be the "primary", that is the one show to the user as the current page. This method will not be invoked when the adapter contains no items.
Not only you have a callback for when the page is visible but this callback also provides the position of the current page.
class MyAdapter extends PagerAdapter {
#Override
public int getCount() {
...
}
#Override
public boolean isViewFromObject(#NonNull #NotNull View view, #NonNull #NotNull Object object) {
...
}
#Override
public void setPrimaryItem(#NonNull #NotNull ViewGroup container, int position, #NonNull #NotNull Object object) {
super.setPrimaryItem(container, position, object);
// `position` gives you the position of the current page
// And this is how I managed to play the animation (Lottie library) when the page is visible to the user
LottieAnimationView animation = ((ViewGroup) object).findViewById(R.id.my_animation_view);
animation.playAnimation();
}
}