Callback

Kotlin |Java

abstract class Callback

kotlin.Any
↳	androidx.recyclerview.widget.DiffUtil.Callback

A Callback class used by DiffUtil while calculating the diff between two lists.

Summary

Public constructors
`<init>()` A Callback class used by DiffUtil while calculating the diff between two lists.

Public methods
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.

Public constructors

<init>

Callback()

A Callback class used by DiffUtil while calculating the diff between two lists.

Public methods

areContentsTheSame

abstract fun areContentsTheSame(
    oldItemPosition: Int, 
    newItemPosition: Int
): Boolean

Called by the DiffUtil when it wants to check whether two items have the same data. DiffUtil uses this information to detect if the contents of an item has changed.

DiffUtil uses this method to check equality instead of Object#equals(Object) so that you can change its behavior depending on your UI. For example, if you are using DiffUtil with a RecyclerView.Adapter, you should return whether the items' visual representations are the same.

This method is called only if areItemsTheSame(int, int) returns true for these items.

Parameters
`oldItemPosition`	Int: The position of the item in the old list
`newItemPosition`	Int: The position of the item in the new list which replaces the oldItem

Return
`Boolean`	True if the contents of the items are the same or false if they are different.

areItemsTheSame

abstract fun areItemsTheSame(
    oldItemPosition: Int, 
    newItemPosition: Int
): Boolean

Called by the DiffUtil to decide whether two object represent the same Item.

For example, if your items have unique ids, this method should check their id equality.

Parameters
`oldItemPosition`	Int: The position of the item in the old list
`newItemPosition`	Int: The position of the item in the new list

Return
`Boolean`	True if the two items represent the same object or false if they are different.

getChangePayload

@Nullable open fun getChangePayload(
    oldItemPosition: Int, 
    newItemPosition: Int
): Any?

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.

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.

Default implementation returns null.

Parameters
`oldItemPosition`	Int: The position of the item in the old list
`newItemPosition`	Int: The position of the item in the new list

Return
`Any?`	A payload object that represents the change between the two items.

getNewListSize

abstract fun getNewListSize(): Int

Returns the size of the new list.

Return
`Int`	The size of the new list.

getOldListSize

abstract fun getOldListSize(): Int

Returns the size of the old list.

Return
`Int`	The size of the old list.