问题
While using a ListAdapter I noticed that after updating an item the DiffUtil.ItemCallback areContentsTheSame() method was always returning true. Debugging the code I realized that the old and the new item were exactly the same (the old state disappeared). Therefore the ListAdapter onBindViewHolder() method wasn't being called to update the respective row on the list (only the order of the items changed with a nice animation).
Checking other questions on Stackoverflow looks like it's a common issue that many developers have faced:
ListAdapter not updating item in reyclerview
ListAdapter not updating when editing content
DiffUtil.Callback not working as expected
Items in Recyclerview + Listadapter won't redraw on update
ListAdapter with DiffUtil.ItemCallback always considers objects the same
When submitting a new list to RecyclerView ListAdapter the diff check always returns true for areContentsTheSame()
However none of the above answers (if any) have provided a correct solution.
The only way it worked for me was by calling notifyDataSetChanged() on the ListAdapter everytime the observer emitted a new result.
But what's the whole point of using a ListAdapter and submitList() to notify changes if all the great performance you could get is thrown away by forcing the RecyclerView to redraw its content (all the items it has showed so far)?
notifyDataSetChanged():
Even though it works, certainly is not the proper approach to go with if you decided to use a ListAdapter in first place.
viewModel.getObjects().observe(this, listOfObjects -> listAdapter.submitList(new ArrayList<>(listOfObjects)));:
Didn't work.
After updating a item in the list I would like to see the respective changes taking place on the UI (not only the sorting order) for the corresponding row as expected.
回答1:
I spent a lot of time until I found out that I was having the same issue as described on this post. I tried many solutions, but in the end I realised that I was messing it up without knowing. If you're having this same issue, check if you aren't updating the UI first and calling a write command to update the value on your repository. In my case, I was updating the LiveData object and then updating that value on Firebase Database. The issue was being caused because my UI was listening to changes on that LiveData object, so my Firebase Database observer detected changes, the ListAdapter was called and it looked like nothing has been changed.
To solve the problem, I dropped the lines that were updating the LiveData object and I only called Firebase Database sending the changes.
来源：https://stackoverflow.com/questions/57876118/diffutil-itemcallback-arecontentsthesame-always-returns-true-after-updating-an