DiffUtil is a utility class that calculates the difference between two lists and outputs a list of update operations that converts the first list into the second one.
It can be used to calculate updates for a RecyclerView Adapter. See ListAdapter and AsyncListDiffer which can simplify the use of DiffUtil on a background thread.
DiffUtil uses Eugene W. Myers's difference algorithm to calculate the minimal number of updates to convert one list into another. Myers's algorithm does not handle items that are moved so DiffUtil runs a second pass on the result to detect items that were moved.
Note that DiffUtil, ListAdapter, and AsyncListDiffer require the list to not mutate while in use. This generally means that both the lists themselves and their elements (or at least, the properties of elements used in diffing) should not be modified directly. Instead, new lists should be provided any time content changes. It's common for lists passed to DiffUtil to share elements that have not mutated, so it is not strictly required to reload all data to use DiffUtil.
If the lists are large, this operation may take significant time so you are advised to run this on a background thread, get the DiffUtil.DiffResult then apply it on the RecyclerView on the main thread.
DiffUtil.Callback class used by DiffUtil while calculating the diff between two lists.
Method |
Description |
|---|---|
abstract Boolean areContentsTheSame(oldItemPosition: Int, newItemPosition: Int) |
Called by the DiffUtil when it wants to check whether two items have the same data. |
abstract Boolean areItemsTheSame(oldItemPosition: Int, newItemPosition: Int) |
Called by the DiffUtil to decide whether two object represent the same Item. |
open Any? getChangePayload(oldItemPosition: Int, newItemPosition: Int) |
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. |
abstract Int getNewListSize() |
Returns the size of the new list. |
abstract Int getOldListSize() |
Returns the size of the old list. |
https://developer.android.com/reference/androidx/recyclerview/widget/DiffUtil
https://developer.android.com/reference/kotlin/androidx/recyclerview/widget/DiffUtil.Callback
https://medium.com/@iammert/using-diffutil-in-android-recyclerview-bdca8e4fbb00