To properly implement a DiffUtil.ItemCallback<T> passed inside the constructor of ListAdapter, both areItemsTheSame and areContentsTheSame must be implemented.

Now for areItemsTheSame it is advised that a unique identifier of type of . So for my case where is a data class without a deducible unique identifier, how am I supposed to implement it properly? When simply doing oldItem == newItem in both functions, I obviously get a flashing animation on the item since it thinks it's a completely different item since areItemsTheSame returned false.

So how do people fix this properly? Would returning true anyway if the data type is the same which would then trigger the areContentsTheSame be a fix? And if not, why? If I do that currently, the recycler properly understands that just some data has changed, and only the necessary parts of the view "flash" with the new data.

CodePudding user response：

So how do people fix this properly?

The "solution" is to have a unique identifier for each row (which is good advice for most relational data structures).

You can combine fields in either method, the callback offers you both items (old and new) and you get to decide what to do/compare in there.

When the items "are the same" (as determined by your implementation), then this allows the RecyclerView/Adapter combo to make assumptions (and optimizations).

When the items are determined to have changed (meaning they are now two different items), then a different set of things must happen (animations, rebinding, determining the viewType, etc.). More work for the UI.

So don't fight the framework, instead provide a unique identifier, even if it's composed of more than one field. I'm curious to see your data class to understand how comes there's no unique way to identify a single row.