Develop Reference

Item animation stopping in recyclerview when scrolled off the view android

I have a Recyclerview, im animating a view inside individual list item, but when I scroll the recyclerview the animation is stopping. Its because recyclerview removes the items form its view so when we scroll back it fetches it back! But now i want that animation to keep going as I would stop it only when i get data from server!
All I want is the animation that I start in the individual items inside the recylerview shouldn't stop even if the recyclerview is scrolled and the view is out of focus and comes back to focus! I need to stop the animation in the code when I get the server data! I have the code where to stop the animation and it works if the item is not scrolled off the view!
btn.onClick -- this button is the onClick for the recyclerview list
item 1 btn.startAnimation(anim.xml) -- starting the animation
onSuccess -- server returns success btn.clearAnimation();
but before the onSuccess if we scroll the list the animation is stopped!
Please help!

By inspiring from crymson's answer i have made little easy and useful solution using tag method of View instead setting a boolean in complicated logic of your custom adapter.
#Override
public void onViewDetachedFromWindow(RecyclerView.ViewHolder holder) {
super.onViewDetachedFromWindow(holder);
if (holder.getItemViewType() == TYPE_AD)
((ViewHolderForAd) holder).ivStory.setTag(false);
}
public class ViewHolderForAd extends RecyclerView.ViewHolder {
private ImageView ivStory;
TextView tvName;
public ViewHolderForAd(View view) {
super(view);
ivStory = (ImageView) view.findViewById(R.id.ivStoryImage);
tvName = (TextView) view.findViewById(R.id.tvAppName);
view.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v) {
int pos = getAdapterPosition();
if (pos < 0) {
pos = (int) v.getTag();
}
customItemClickListener.onItemClicked(v, pos);
}
});
//ivStory.startAnimation(AnimationUtils.loadAnimation(context, R.anim.pulse_story));
ivStory.setTag(false); //Set default tag false to decrease risk of null
}
}
#Override
public void onBindViewHolder(RecyclerView.ViewHolder viewHolder, int i) {
//...Your code...
if (!(boolean) holder1.ivStory.getTag()) {
holder1.ivStory.setTag(true);
holder1.ivStory.startAnimation(AnimationUtils.loadAnimation(context, R.anim.pulse_story));
}
//...Your code...//
}
You can use setTag(key, object) instead of setTag(object) if you already tagged something(like position) in your imageView.
Hope this helps someone.

Hard to give you a full solution but have you tried saving the animation state inside the ViewHolder that you are using? I'd recommend saving a boolean flag in the ViewHolder class you defined like isAnimating which is initially set to false and in your onBindViewHolder(...) method you can do something like
if (viewHolder.isAnimating) {
// start animation
} else {
// clear animation
}
viewHolder.btn.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
viewHolder.isAnimating = true;
// start animation
}
});

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);

InfiniteViewPager freezes on setCurrentItem() method

I am using this code to create InfiniteViewPager:
pAdapter = new InfinitePagerAdapter(new MyPagerAdapter());
InfinitivePAdapter = (InfiniteViewPager) findViewById(R.id.pager);
InfinitivePAdapter.setAdapter(pAdapter);
There seems to be something wrong with setCurrentItem() function.
The program freezes when I try call setCurrentItem() function, but not everytime. The program freezes only when:
The setCurrentItem()'s item is lower and it is called from different method(in my case from onClickListener).
InfinitivePAdapter.setCurrentItem(7);//item is set on 7
button.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v) {
InfinitivePAdapter.setCurrentItem(5);//when button is pressed it is set to 5
}
});
However program seems to be working normal when:
Item is bigger then previous one:
InfinitivePAdapter.setCurrentItem(3);//item is set on 3
button.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v) {
InfinitivePAdapter.setCurrentItem(12);//when button is pressed it is set to 12
}
});
or the setCurrentItem(3) is called one after another even though the item is smaller than previous one:
InfinitivePAdapter.setCurrentItem(7);
InfinitivePAdapter.setCurrentItem(5);
More precisely program freezes in InfiniteViewPager class on this line:
#Override
public void setCurrentItem(int item) {
// offset the current item to ensure there is space to scroll
item = getOffsetAmount() + (item % getAdapter().getCount());
super.setCurrentItem(item);//<---HERE
}
I got my InfiniteViewPager from https://github.com/antonyt/InfiniteViewPager
You can download full code here:https://drive.google.com/folderview?id=0B3LJrVAKNLR1OG8yeERyQ2ZySU0&usp=sharing
Thanks!

I figured it out. In the InfinitePagerAdapter class I just changed the return value of getCount() method.
#Override
public int getCount() {
return Integer.MAX_VALUE;
}
Integer.MAX_VALUE was too big of a value so scale it down to 3000:
return 3000;//Or something similar
The problem was in the ViewPager class where on line 1029 the for loop would never finished:
for (int pos = mCurItem + 1; pos < N; pos++)
//N is the return Integer.MAX_VALUE and the mCurItem is the item set in setCurrentItem() method

Does android PageAdapter and ViewPager check for indexoutofbounds exception when using setCurrentItem(int index)?

So my activity uses the PageAdapter and ViewPager correctly, where 3 images can be scrolled from left to right. So then I have left and right arrows on the activity and I set an onClickListener for both images to scroll left and right with ViewPager pager. The method is like
private void setOnClickArrows(final ViewPager pager){
ImageView rightArrow = (ImageView) view.findViewById(R.id.right);
ImageView leftArrow = (ImageView) view.findViewById(R.id.left);
rightArrow.setOnClickListener(new OnClickListener ()
#Override
public void onClick(View v) {
pager.setCurrentItem(pager.getCurrentItem() + 1);
}
});
leftArrow.setOnClickListener(new OnClickListener ()
#Override
public void onClick(View v) {
pager.setCurrentItem(pager.getCurrentItem() - 1);
}
});
}
This works perfectly. However, I was wondering how the ViewPager checks if the index is out of bounds and if I should do it?

Yes, it actually does. Refer to the source and have a look at the setCurrentItemInternal method (called by setCurrentItem()).
There are a few checks in place to avoid a crash, and among one of them is this, which avoids OOBExceptions:
if (item < 0) {
item = 0;
} else if (item >= mAdapter.getCount()) {
item = mAdapter.getCount() - 1;
}
Should you check yourself? Up to you. I wouldn't because those checks are trivial, so I wouldn't expect the checks to disappear.

Adding items to ListView, maintaining scroll position and NOT seeing a scroll jump

I'm building an interface similar to the Google Hangouts chat interface. New messages are added to the bottom of the list. Scrolling up to the top of the list will trigger a load of previous message history. When the history comes in from the network, those messages are added to the top of the list and should not trigger any kind of scroll from the position the user had stopped when the load was triggered. In other words, a "loading indicator" is shown at the top of the list:
Which is then replaced in-situ with any loaded history.
I have all of this working... except one thing that I've had to resort to reflection to accomplish. There are plenty of questions and answers involving merely saving and restoring a scroll position when adding items to the adapter attached to a ListView. My problem is that when I do something like the following (simplified but should be self-explanatory):
public void addNewItems(List<Item> items) {
final int positionToSave = listView.getFirstVisiblePosition();
adapter.addAll(items);
listView.post(new Runnable() {
#Override
public void run() {
listView.setSelection(positionToSave);
}
});
}
Then what the user will see is a quick flash to the top of the ListView, then a quick flash back to the right location. The problem is fairly obvious and discovered by many people: setSelection() is unhappy until after notifyDataSetChanged() and a redraw of ListView. So we have to post() to the view to give it a chance to draw. But that looks terrible.
I've "fixed" it by using reflection. I hate it. At its core, what I want to accomplish is reset the first position of the ListView without going through the rigamarole of the draw cycle until after I've set the position. To do that, there's a helpful field of ListView: mFirstPosition. By gawd, that's exactly what I need to adjust! Unfortunately, it's package-private. Also unfortunately, there doesn't appear to be any way to set it programmatically or influence it in any way that doesn't involve an invalidate cycle... yielding the ugly behavior.
So, reflection with a fallback on failure:
try {
Field field = AdapterView.class.getDeclaredField("mFirstPosition");
field.setAccessible(true);
field.setInt(listView, positionToSave);
}
catch (Exception e) { // CATCH ALL THE EXCEPTIONS </meme>
e.printStackTrace();
listView.post(new Runnable() {
#Override
public void run() {
listView.setSelection(positionToSave);
}
});
}
}
Does it work? Yes. Is it hideous? Yes. Will it work in the future? Who knows? Is there a better way? That's my question.
How do I accomplish this without reflection?
An answer might be "write your own ListView that can handle this." I'll merely ask whether you've seen the code for ListView.
EDIT: Working solution with no reflection based on Luksprog's comment/answer.
Luksprog recommended an OnPreDrawListener(). Fascinating! I've messed with ViewTreeObservers before, but never one of these. After some messing around, the following type of thing appears to work quite perfectly.
public void addNewItems(List<Item> items) {
final int positionToSave = listView.getFirstVisiblePosition();
adapter.addAll(items);
listView.post(new Runnable() {
#Override
public void run() {
listView.setSelection(positionToSave);
}
});
listView.getViewTreeObserver().addOnPreDrawListener(new OnPreDrawListener() {
#Override
public boolean onPreDraw() {
if(listView.getFirstVisiblePosition() == positionToSave) {
listView.getViewTreeObserver().removeOnPreDrawListener(this);
return true;
}
else {
return false;
}
}
});
}
Very cool.

As I said in my comment, a OnPreDrawlistener could be another option to solve the problem. The idea of using the listener is to skip showing the ListView between the two states(after adding the data and after setting the selection to the right position). In the OnPreDrawListener(set with listViewReference.getViewTreeObserver().addOnPreDrawListener(listener);) you'll check the current visible position of the ListView and test it against the position which the ListView should show. If those don't match then make the listener's method return false to skip the frame and set the selection on the ListView to the right position. Setting the proper selection will trigger the draw listener again, this time the positions will match, in which case you'd unregister the OnPreDrawlistener and return true.

I was breaking up my head until I found a solution similar to this.
Before adding a set of items you have to save top distance of the firstVisible item and after adding the items do setSelectionFromTop().
Here is the code:
// save index and top position
int index = mList.getFirstVisiblePosition();
View v = mList.getChildAt(0);
int top = (v == null) ? 0 : v.getTop();
// for (Item item : items){
mListAdapter.add(item);
}
// restore index and top position
mList.setSelectionFromTop(index, top);
It works without any jump for me with a list of about 500 items :)
I took this code from this SO post: Retaining position in ListView after calling notifyDataSetChanged

The code suggested by the question author works, but it's dangerous.
For instance, this condition:
listView.getFirstVisiblePosition() == positionToSave
may always be true if no items were changed.
I had some problems with this aproach in a situation where any number of elements were added both above and below the current element. So I came up with a sligtly improved version:
/* This listener will block any listView redraws utils unlock() is called */
private class ListViewPredrawListener implements OnPreDrawListener {
private View view;
private boolean locked;
private ListViewPredrawListener(View view) {
this.view = view;
}
public void lock() {
if (!locked) {
locked = true;
view.getViewTreeObserver().addOnPreDrawListener(this);
}
}
public void unlock() {
if (locked) {
locked = false;
view.getViewTreeObserver().removeOnPreDrawListener(this);
}
}
#Override
public boolean onPreDraw() {
return false;
}
}
/* Method inside our BaseAdapter */
private updateList(List<Item> newItems) {
int pos = listView.getFirstVisiblePosition();
View cell = listView.getChildAt(pos);
String savedId = adapter.getItemId(pos); // item the user is currently looking at
savedPositionOffset = cell == null ? 0 : cell.getTop(); // current item top offset
// Now we block listView drawing until after setSelectionFromTop() is called
final ListViewPredrawListener predrawListener = new ListViewPredrawListener(listView);
predrawListener.lock();
// We have no idea what changed between items and newItems, the only assumption
// that we make is that item with savedId is still in the newItems list
items = newItems;
notifyDataSetChanged();
// or for ArrayAdapter:
//clear();
//addAll(newItems);
listView.post(new Runnable() {
#Override
public void run() {
// Now we can finally unlock listView drawing
// Note that this code will always be executed
predrawListener.unlock();
int newPosition = ...; // Calculate new position based on the savedId
listView.setSelectionFromTop(newPosition, savedPositionOffset);
}
});
}