This document discusses various techniques for optimizing RecyclerView performance in Android applications. It begins by describing common ways to measure UI performance such as frames per second (FPS), GPU rendering profiling, and aggregating frame stats. The document then provides tips for optimizing RecyclerView cells hierarchies, minimizing work done in onBindViewHolder(), correctly scaling images, handling nested RecyclerViews, only updating affected items, using item caches, stable IDs, prefetching, and DiffUtil.

1. RecylerView
Performance Tuning
Oleksandr Tolstykh
@a_tolstykh
Head of Mobile Development,
Android engineer

3. How to measure UI performance?
● FPS
https://github.com/friendlyrobotnyc/TinyDancer
● Profile GPU rendering
https://developer.android.com/studio/profile/dev-options-rendering.html
● Aggregate frame stats
https://developer.android.com/training/testing/performance.html
● Many others...
@a_tolstykh

4. How to measure UI performance?
● FPS
https://github.com/friendlyrobotnyc/TinyDancer
● Profile GPU rendering
https://developer.android.com/studio/profile/dev-options-rendering.html
● Aggregate frame stats
https://developer.android.com/training/testing/performance.html
● Many others...
@a_tolstykh

5. Sample App - Travel With Us
City guides
Base city info
Data is loaded from server
@a_tolstykh
RecyclerView!

6. Optimize Cells hierarchies
Avoid deep hierarchy
Save level with <merge> when <include>
Layout matters!
@a_tolstykhhttps://developer.android.com/topic/performance/rendering/optimizing-view-hierarchies.html
android.support.constraint.ConstraintLayout
com.google.android.flexbox.FlexboxLayout

7. Minimize onBindViewHolder()
Make onBindViewHolder() as cheap as possible
Avoid item instantiations (memory allocations)
Do as much as you can in onCreateViewHolder()
@a_tolstykh

8. Correct images scale
Make sure their size and compression are optimal.
Scaling images may also affect the performance.
Do not reinvent the wheel.
@a_tolstykh
Picasso, ImageLoader, Fresco, Glide.
Picasso v/s Imageloader v/s Fresco vs Glide [closed]
http://stackoverflow.com/q/29363321/2308720

9. Nested RecyclerView
Override the LinearLayoutManager#getInitialPrefetchItemCount()
@a_tolstykh
public int getInitialPrefetchItemCount ()
Defines how many inner items should be prefetched when this LayoutManager's
RecyclerView is nested inside another RecyclerView
Binding the inner RecyclerView doesn’t allocate any children.
The prefetching system has to know how many.

10. Update only the affected items
adapter.notifyItemRemoved(position);
adapter.notifyItemChanged(position);
adapter.notifyItemInserted(position);
* only if you know position of updated item
@a_tolstykh

11. Profit!
Animations for free!
Optimizations for free!
@a_tolstykh

12. Remove an item with swipe:
SimpleCallback touchCallback
= new SimpleCallback(0, ItemTouchHelper.LEFT | ItemTouchHelper.RIGHT) {
// ...
@Override
public void onSwiped(ViewHolder viewHolder, int swipeDir) {
adapter.remove(viewHolder.getAdapterPosition());
adapter.notifyItemRemoved(viewHolder.getAdapterPosition());
}
};
@a_tolstykh

13. Items cache
recyclerView.setItemViewCacheSize (int size);
Documentation:
“Set the number of offscreen views
to retain before adding them
to the potentially shared recycled view pool.”
@a_tolstykh
static final int DEFAULT_CACHE_SIZE = 2; // supportVersion = 25.3.0

14. Stable ids - adapter.setHasStableIds()
adapter.setHasStableIds(true);
// YourAdapter.java
@Override
public long getItemId(int position) {
return items.get(position).hashcode(); //id()
}
@a_tolstykh
Only if item in the data set can be represented with a unique identifier
Avoid unnecessary bindViewHolder() calls if view exists in RecyclerView’s cache

15. Prefetch
Use latest version of support library to use native prefetch optimizations
supportVersion >= 25.1.0
// (enabled by default)
RecyclerView Prefetch by Chet Haase
https://medium.com/google-developers/c2f269075710
*Lollipop and newer
@a_tolstykh

16. Advanced prefetch
Override the LinearLayoutManager#getExtraLayoutSpace(RecyclerView.State s)
@a_tolstykh
protected int getExtraLayoutSpace (RecyclerView.State state)
Returns the amount of extra space that should be laid out by LayoutManager.
By default, LinearLayoutManager lays out 1 extra page of items while smooth
scrolling and 0 otherwise. You can override this method to implement your custom
layout pre-cache logic.

17. Advanced prefetch
@a_tolstykh
public class PreCachingLayoutManager extends LinearLayoutManager {
// ....
public void setExtraLayoutSpace(int extraLayoutSpace) {
this.extraLayoutSpace = extraLayoutSpace;
}
@Override
protected int getExtraLayoutSpace(RecyclerView.State state) {
return extraLayoutSpace > 0 ? extraLayoutSpace : DEFAULT_EXTRA_SPACE;
}
}

18. BUT...
Expensive if done while the user may change scrolling direction.
Laying out invisible elements generally comes with significant performance cost.
Useless without increasing cache size (setItemViewCacheSize).
@a_tolstykh
BUT it improves USER EXPERIENCE!
Need to find balance.
Maybe 1 extra screen is The Balance?

19. Even more advanced prefetch...
Prefetch images! (on wi-fi only)
@a_tolstykh
Picasso.with(context).load(url).fetch();
Glide.with(context).load(url).downloadOnly(width, height);

20. @a_tolstykh
Without
images
prefetch
With
images
prefetch
Images
prefetch

21. @a_tolstykh
public class CitiesAdapter extends RecyclerView.Adapter<CityViewHolder> {
public void updateData(List<City> cities) {
if (onWifi()) prefetch(cities);
// TODO update adapter data
}
private void prefetch(List<City> cities) {
for (City city : cities) {
PreFetcher prefetcher = city.getPrefetcher();
if (prefetcher != null) {
prefetcher.prefetch(mContext);
}
}
}
}

22. @a_tolstykh
public class ImagePrefetcher implements PreFetcher {
private final Image[] mImages;
public ImagePrefetcher(Image... images) {
this.mImages = images;
}
@Override
public void prefetch(Context context) {
for (Image image : mImages) {
Picasso.with(context).load(image.url()).fetch();
}
}
}

23. @a_tolstykh
public class TweetPrefetcher implements PreFetcher {
private final List<String> mIds;
@Override
public void prefetch(Context context) {
TwitterHelper.loadTweets(mIds, new Callback<List<Tweet>>() {
@Override
public void success(Result<List<Tweet>> result) {
for (Tweet tweet : result.data) {
TwitterHelper.preFetchTweetImage(tweet);
}
}
});
}
}

24. Displayed data pre-calculations
Displayed items are POJOs.
Pre-format date, time, other strings during data parsing.
Pre-calculate immutable values during data parsing.
@a_tolstykh
Profit:
+ Minor performance optimisations.
+ Formatting is done in BG thread.
+ Formatting is done in single place.

25. Displayed data pre-calculations (formatting)
@WorkerThread
private static Rating createRating(float value, int count) {
String ratingFormatted = String.format(Locale.US, "%.1f", value);
String countFormatted = formatWithMetricPrefix(count);
return Rating.create(value, ratingFormatted, count, countFormatted);
}
@UiThread
public void setRating(Rating rating) {
ratingText.setText(rating.ratingFormatted());
reviewsCount.setText(rating.numberOfReviewsFormatted());
}
@a_tolstykh

26. DiffUtil
@a_tolstykh
*since support library version 24.2.0
https://developer.android.com/reference/android/support/v7/util/DiffUtil.html

27. android.support.v7.util.DiffUtil
Documentation:
“DiffUtil is a utility class that can calculate the difference between two
lists and output a list of update operations that converts the first list
into the second one.
@a_tolstykh
It can be used to calculate updates for a RecyclerView Adapter.”
DiffUtil.Callback cb = new YourDiffCallback(oldList, newList);
DiffUtil.DiffResult diffResult = DiffUtil.calculateDiff(cb);
diffResult.dispatchUpdatesTo(adapter);

28. DiffUtil.Callback
public class DiffCallback extends DiffUtil.Callback {
public DiffCallback(@NonNull List<City> newList, @NonNull List<City> oldList) {...}
public int getOldListSize() {...}
public int getNewListSize() {...}
public boolean areItemsTheSame(int oldItemPosition, int newItemPosition) {...}
public boolean areContentsTheSame(int oldItemPosition, int newItemPosition) {...}
@Nullable
public Object getChangePayload(int oldItemPosition, int newItemPosition) {...}
}
@a_tolstykh

29. DiffUtil.Callback
public boolean areItemsTheSame(int oldItemPosition, int newItemPosition)
When areItemsTheSame(int, int) returns true for two items and areContentsTheSame(int,
int) returns false for them, DiffUtil calls this method to get a payload about the change.
public boolean areContentsTheSame(int oldItemPosition, int newItemPosition)
Checks whether two items have the same data.You can change its behavior depending on
your UI. This method is called by DiffUtil only if areItemsTheSame returns true.
@a_tolstykh

30. DiffUtil.Callback
@Override public int getOldListSize() {
return oldCities.size();
}
@Override public int getNewListSize() {
return newCities.size();
}
@Override public boolean areItemsTheSame(int oldPosition, int newPosition) {
return oldCities.get(oldPosition).id() == newCities.get(newPosition).id();
}
@Override public boolean areContentsTheSame(int oldPosition, int newPosition) {
return oldCities.get(oldPosition).equals(newCities.get(newPosition));
}
@a_tolstykh

31. @a_tolstykh
Without
DiffUtil
With
DiffUtil
Lenovo Vibe X
Android OS, v4.2
1080 x 1920 pixels
Quad-core 1.5 GHz

32. DiffUtil.Callback
public Object getChangePayload(int oldItemPosition, int newItemPosition)
When areItemsTheSame(int, int) returns true for two items and areContentsTheSame(int,
int) returns false for them, DiffUtil calls this method to get a payload about the change.
@a_tolstykh
For example, if you are using DiffUtil with RecyclerView, you can return
the particular field that changed in the item and your ItemAnimator can
use that information to run the correct animation.

33. DiffUtil animated values change
public Object getChangePayload(int oldItemPosition, int newItemPosition) {
Bundle diff = new Bundle();
Rating newRating = newCities.get(newItemPosition).rating();
Rating oldRating = oldCities.get(oldItemPosition).rating();
if (newRating.numberOfReviews() != oldRating.numberOfReviews()) {
diff.putString(KEY_NUMBER_OF_REVIEWS, newRating.numberOfReviewsFormatted());
}
if (Float.compare(newRating.rating(), oldRating.rating()) != 0) {
diff.putString(KEY_RATING_FORMATTED, newRating.ratingFormatted());
}
return diff.size() == 0 ? null : diff;
}
@a_tolstykh

34. public void onBindViewHolder(CityViewHolder holder, int index, List<Object> p) {
if (p.isEmpty()) {
onBindViewHolder(holder, index);
return;
}
Bundle payload = (Bundle) p.get(0);
for (String key : payload.keySet()) {
if (key.equals(CitiesDiffCallback.KEY_NUMBER_OF_REVIEWS)) {
holder.animateReviews(payload.getString(key));
} else if (key.equals(CitiesDiffCallback.KEY_RATING_FORMATTED)) {
holder.animateRating(payload.getString(key));
}
}
}
@a_tolstykh

35. Use any animation you want!
● android.widget.TextSwitcher
● com.hanks.htextview.HTextView
● custom...
@a_tolstykh
DiffUtil animated values change

36. DiffUtil - average runtimes
● 100 items and 10 modifications: avg: 0.39 ms, median: 0.35 ms
● 100 items and 100 modifications: 3.82 ms, median: 3.75 ms
● 100 items and 100 modifications without moves: 2.09 ms, median: 2.06 ms
● 1000 items and 50 modifications: avg: 4.67 ms, median: 4.59 ms
● 1000 items and 50 modifications without moves: avg: 3.59 ms, median: 3.50 ms
● 1000 items and 200 modifications: 27.07 ms, median: 26.92 ms
● 1000 items and 200 modifications without moves: 13.54 ms, median: 13.36 ms
tests are run on Nexus 5X with M
@a_tolstykh

37. DiffUtil
May take significant time for large dataset...
@a_tolstykh
Use it on a background thread!

38. DiffUtil. Summary
Avoid unnecessary UI updates!
@a_tolstykh
Animated values change!

39. Android TextView with rich support
of compound drawables.
This is a tiny library which empowers
TextView's compound drawables with:
● size specifying
● vector support
● tinting
@a_tolstykhhttps://github.com/a-tolstykh/textview-rich-drawable
TextViewRichDrawable

40. <TextView android:id="@+id/reviews_count"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
<ImageView android:layout_width="@dimen/icon_small_size"
android:layout_height="@dimen/icon_small_size"
android:layout_marginEnd="@dimen/space_medium"
android:src="@drawable/ic_person" />
<TextView android:id="@+id/rating_value"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
<ImageView android:layout_width="@dimen/icon_small_size"
android:layout_height="@dimen/icon_small_size"
android:src="@drawable/ic_star" />
@a_tolstykh
<com.tolstykh.textviewrichdrawable.TextViewRichDrawable
android:id="@+id/reviews_count"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginEnd="@dimen/space_medium"
android:drawableRight="@drawable/ic_person"
app:compoundDrawableHeight="@dimen/icon_small_size"
app:compoundDrawableWidth="@dimen/icon_small_size" />
<com.tolstykh.textviewrichdrawable.TextViewRichDrawable
android:id="@+id/rating_value"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:drawableRight="@drawable/ic_star"
app:compoundDrawableHeight="@dimen/icon_small_size"
app:compoundDrawableWidth="@dimen/icon_small_size" />
Before After
https://github.com/a-tolstykh/textview-rich-drawable

41. Simplify your layout
@a_tolstykh
Before After
https://github.com/a-tolstykh/textview-rich-drawable
4 Views 2 Views

42. RecyclerView Performance Tuning
Prefetch. Cache. Reuse!
@a_tolstykh

43. RecyclerView Performance Tuning
Do not over engineer. Keep it simple!
@a_tolstykh

44. RecyclerView Performance Tuning
Avoid premature optimizations. Think about
optimizations when you need them.
@a_tolstykh

45. Thanks
@a_tolstykh
@a_tolstykh
@a_tolstykh
+OleksandrTolstykh