Introduce support for diffing subsets of data in generic RecyclerView adapter

[BenHenning]

The initial implementation of the generic RecyclerView BindableAdapter notifies that the whole data set is changed for each re-bind, which is sometimes wrong (the data may be the same) and highly inefficient (1 element might have changed out of hundreds). Diffing logic should be introduced to only notify that a subset of the data has changed, which also enables support for RecyclerView animations.

[anandwana001]

@BenHenning Tried this issue using AsyncListDiffer and setting the new data inside our setData(newDataList: List<T>) with differ.submitList(buildNewList(newDataList))

Video link - https://drive.google.com/drive/folders/1HAfzcLl2BkSddAjuUuCBJAmf5RwP9Atn?usp=sharing

Before

After

[BenHenning]

Reopened due to revert: https://github.com/oppia/oppia-android/pull/1627.

[khushal1707]

@anandwana001 I like to take this issue, could you give me few pointers on what was the problem with implementation of DiffUtil? Were test cases complete and passing?

[anandwana001]

@khushal1707 Things which are failing:

1. RecyclerView loading is smooth but slow
2. Drag and Drop doesn't work correctly

These are the 2 issues we face after merging my earlier pr

1. https://github.com/oppia/oppia-android/issues/1625
2. https://github.com/oppia/oppia-android/issues/1626

[aggarwalpulkit596]

@anandwana001 didn't we solved this earlier ?

[anandwana001]

No, the linking thing in drag and drop doesn't work with the diffing.

[aggarwalpulkit596]

I'll take a look at it today i believe i have a solution for this

[anandwana001]

Thanks, this will be helpful.

[khushal1707]

@anandwana001 So the problem which I understood is that grouping items doesn't invoke DiffUtil, whereas on dragging and dropping it refreshes and shows the the grouped item. I haven't found any function in DiffUtil to solve this issue but there is a workaround which invoke DiffUtil to refresh list i.e. to call function onItemMoved() in DragAndDropSortInteractionViewModel twice such that its effect on the list got nullify( this is just the workaround and doesn't completely solves the problem ). So should I implements these workarounds or try something else?

[anandwana001]

let's have. a draft pr, which solves this issue and will discuss more on this. Also, keeping @aggarwalpulkit596 in loop for drag and drop feature.

[khushal1707]

Sure!

[aggarwalpulkit596]

OnItemMoved won't work correctly if i remember what i did while trying to fix this.

[khushal1707]

OnItemMoved won't work correctly if i remember what i did while trying to fix this.

Yes, it didn't refresh when there is only one item on list and also cashes app sometimes. Is there any other way to invoke DiffUtil when grouping occurs @aggarwalpulkit596 ?

[aggarwalpulkit596]

I'd have to try it out myself first it's been quite some time 😅

[khushal1707]

I'd have to try it out myself first it's been quite some time 😅

Okay, till then I also try to figure out something and if something works I'll make a draft PR and notify.

[khushal1707]

Hi @anandwana001 @aggarwalpulkit596, can we use notifyDataSetChanged() for nested recyclerview of DragAndDropSortInteraction only after merging in DragAndDropSortInteractionViewModel and use Diffing in main and other recyclerviews. Merging works fine with this approach.

[khushal1707]

@anandwana001 @aggarwalpulkit596 PTAL: https://github.com/oppia/oppia-android/pull/2666 Haven't added tests yet, will be adding as soon as issue with diffing resolves. Thanks!