I have an adapter that displays a grid of thumbnails with a text. These thumbnails are heavy to load, heavy to draw, etc.
The thumbnail gridview is constantly filled with new content, let's say, 1 new item every 2 seconds.
My adapter has a function that I call from outside to inject new items:
public void postNew(Item i) {
arrayStuff.put(i);
notifyDataSetChanged();
}
What happens is, with my current approach, when I insert a new element in the gridview, it refreshes everything, even if the added item is not going to be visible. The refresh process kind of breaks the experience, specially if the user is browsing the gridview and new content arrives.
How would you recommend improving this? is there a lighter 'notifyDataSetChanged()' or something like that?
I do not know of any lighter version of notify data set, but you can always use ListView.getFirstVisiblePosition and ListView.getLastVisiblePosition to determine whether your latest added position is visible, and only call notifyDataSetChanged if it is.
As for "heavy" bitmaps, as heavy as it is I think you should resample or scale it to the minimum size you need, using LruCache you can reduce the need of re-drawing on notify data set changed.
It sounds like you probably need to implement some form of caching, it's not very good memory management to have images which are not visible loaded into memory, ideally you would retrieve them from cache when they become (or are about to become) visible.
An alternative approach could be to add some form of visual indicator when new content arrives and then implement "pull down to refresh" or similar, then make a call to notifyDataSetChanged() on your adapter to refresh the content. I can imagine that refreshing every couple of seconds would not give a great UX because it would be hard to follow if the screen content is constantly changing.
You need create custom view(dynamic at runtime) that adds multiple imageview and appropriate textview, the container view should be LinearLayout, after that you can able to update a particular view or element.
Related
I'm using recycler view with grid view (every item contains a grid) with thumbnail images after adding images in view it start uploading, and i need to change some values (status) in model at the time of start and finish upload.
What I'm currently doing is change values in model and call notifyDataSetChanged, but it causes to slow down application (hang some times) because it updating every child of list :(
Can any one help me with this?
Call notifydatasetchanged() for particular Gridview adapter only. Don't call notifydatasetchanged() for complete recyclerview adapter.
Try setting it again to the adapter.
gridview.setAdapter(your adapter)
-passing your new list to your adapter.
I believe notifyDataSetChanged updates all of your values regardless if they have a change or not that is why it is slow. I suggest you try using notifyItemChanged(int position) instead.
According to recyclerview docs this is what notifyDataSetChanged does:
This event does not specify what about the data set has changed, forcing any observers to assume that all existing items and structure may no longer be valid. LayoutManagers will be forced to fully rebind and relayout all visible views.
Old question but similar to what I'm experiencing.
RecyclerView is usually incredibly fast when changing list details. But manipulating a lot of images can really slow it down if you're not careul.
I'd recommend you try removing the images and repeat it so you can see if that is just as slow. I suspect this will be a lot faster.
If so, make sure you're handling the images off the UI thread. The Android docs recommend you use a library such as Glide which also handles sub-sampling the image to make sure it's the right size.
Hope that helps!
Background
I'm using the PinterestLikeAdapterView library to show some images from the internet, which is like a gridView but with different height for each cell.
The problem
Since I use this library to show images from the internet, it's crucial that when calling notifyDatasetChanged won't cause a mess on the views.
For some reason, calling this function would call the getView() method with different positions for the views. for example, even though i didn't scroll at all, and call notifyDatasetChanged (or addAll in case it's an ArrayAdapter), for position 0 it will take what was the view of position 8, for position 1 it will take the view of position 7 , and so on...
This makes the whole grid to refresh its images, and so it ruins the UX.
Usually, in both gridView and listView, the way to overcome refreshing is to put the position that was used for the view inside the viewHolder, and if they are equal, it means that they still match.
for example:
... getView(...)
{
//<=inflate a new view if needed
//avoid refreshing view in case it's still the same position:
if(position==holder.position)
return rootView;
holder.position=position;
//<=update the view according to its data
...
}
However, here they re-use other views in a different order so this trick won't work here.
Because of this issue, not only i get refreshes of almost all of the visible views, but since i use DiskCacheLru library, it crashes since it tries to put 2 identical inputSteam data into the same key using 2 threads.
The question
What can I do?
Is this a known bug in the library?
Maybe I'm using a bad way to overcome refreshes?
for now, i use memory cache to at least get items that were cached before, but that's more like a "cure" than a "vaccine"...
Short answer:
Use an image loading library like Picasso that caches most recently used images in memory, so they don't need to be reloaded from the network.
Long answer:
AdapterView does something called View recycling, where Views which are no longer needed to display a position are re-used to display another. (For example, as you scroll down, Views that disappear off the top of the screen are reused for new positions at the bottom of the screen.) Because of this, it's normal for getView() to be passed the same View for more than one position.
This is done for performance reasons: Inflating new Views is hard and takes time, so AdapterView tries to do it as infrequently as possible.
When using a holder, you store references to ImageView and TextView children inside the item's View, so you don't have to look them up with findViewById() each time - you don't usually store anything specific to a particular position, because the View and its holder will often be used for different positions.
Now, when you call notifyDataSetChanged(), AdapterView assumes that the data set has completely changed. The image that was associated with position 8 may no longer be present, or it may be associated with position 12 now. Consequently, all the existing Views are scrapped - but because AdapterView would still like to avoid inflating new Views, they're re-used to display the new data, with no regard for what position they were displaying previously.
This explains why getView() is being passed the same View for different positions, and why visible positions are being refreshed when you call notifyDataSetChanged(). But how to avoid having your images refresh, ruining the user experience?
Use an image loading library like Picasso that caches most recently used images in memory, so they don't need to be reloaded from the network. The refresh will still happen, but it'll be instantaneous.
View getView(int position, View view, ViewGroup parent) will be always called ascendingly, after notifyDataSetChanged().
I guess that, the order of finishing download task will cause this problem.
As you mentioned in your question, keeping the position is a good way to avoid this problem.
Here is another way to solve it, also re-use the imageviews.
Keep a weak reference of each ImageView in download task.
Then wrap the download task in a dummy ColorDrawable.
When getView is called, set the dummy ColorDrawable to ImageView, and start the download. When download is complete, set the downloaded image back to the referenced ImageView in OnPostExecute().
Explanation
http://android-developers.blogspot.jp/2010/07/multithreading-for-performance.html
Source code
https://code.google.com/p/android-imagedownloader/source/checkout
There is a very good example on PinterestLikeListView in GitHub
Here is the library StaggeredGridView
A modified version of Android's experimental StaggeredGridView. Includes own OnItemClickListener and OnItemLongClickListener, selector, and fixed position restore.
You can get library project here library
and you can get Demo project Here
This is very good open source project, so you can use instead of PinterestLikeAdapterView
Hope this library is going to help you out.
seems that the authors of this library have fixed it, after some time i've reported about it:
https://github.com/huewu/PinterestLikeAdapterView/issues/8
I'm trying to show an animation with all Views that I've created from an adapter. When I scroll down, it shows the animation correctly, but when I scroll up, I see these Views recreate themselves and show the animation again. Then, when I scroll down, it happens again.
My assumption is that the mechanism of creating a View from an adapter is to load the View into memory; just the group of Views which are on screen right now (but above and below views are not loaded into memory). These will be loaded again when I scroll to these views, right?
Is there any way to fix this problem?
PS: Sorry for my English, I hope you understand my problem.
My assumption is that the mechanism of creating a View from an adapter
is to load the View into memory; just the group of Views which are on
screen right now (but above and below views are not loaded into
memory)
That's somewhat correct: a ListView will not try to visualize any data that isn't (at least partially) visible. It also 'recycles' views, meaning that any view that isn't currently used to present data to the user and is of the same 'type' as the next data item, may get reused.
Hence you shouldn't rely on persisting data with or make any assumptions about the existence of particular views. In stead, use something that's separate from the views; e.g. the dataset you're visualizing.
Quite often, you'll supply a list of POJOs to a BaseAdapter or ArrayAdapter. You could simply add a boolean to the POJO indicating whether it should animate or not, and change that whenever the animation for that particular item finishes. Alternatively, you could keep track of these values in a separate collection (which is probably the more straightforward approach if you're dealing with a Cursor as data source rather than POJOs).
my viewpager currently only re-renders views that are two views away from what is visually seen.
example (shown respectively)
ViewA, ViewB, CurrentView, ViewD, ViewE
not rendered, rendered, rendered, rendered, not rendered`
how would I force it to reload a particular view X many views away from the currentView, there are some use case scenarios where I want it to, and other cases when I dont want it to. But currently I only know how to reload the entire adapter - where it perhaps pulls from an arraylist
I'm really not sure how to control the Viewpager - very few examples out there. All I know how to do is reset the entire list on "notifyDataSetChanged"
insight appreciated
use this method mViewPager.setOffscreenPageLimit(2) and you can set the limit of offscreen pages
I think your going too need to decouple your view and data logic (array list in this case?). If you don't want the view to change, don't change the data layer. When you call notifyDataSetChanged everything will mimic your data layer. If you want a view to change, change the data layer and call notifyDataSetChanged.
To put it simpler, the view just draws what the data tells it to, and expect that the view could update at any time. It is very similar to how listview works.
Is there a way to call BaseAdapter.notifyDataSetChanged() on a single element in the adapter.
What I am trying to do is update the data and reflect those changes in the containing ListView. The problem is that sometimes the change is so small that it seems ridiculous that I have to refresh the whole view rather than the single item in the view that has been updated.
I am not aware of such method. If it's really important, you can always find individual item view to update. But I don't think that it worth it as Android is pretty efficient in updating list views. So it will not do much extra work (definitelly not going beyond items currently visible on the screen).