DiffUtil.ItemCallback

public abstract class DiffUtil.ItemCallback<T>

Callback for calculating the diff between two non-null items in a list.

Callback serves two roles - list indexing, and item diffing. ItemCallback handles just the second of these, which allows separation of code that indexes into an array or List from the presentation-layer and content specific diffing code.

Parameters
<T>

Type of items to compare.

Summary

Public constructors

Public methods
abstract boolean
areContentsTheSame(@NonNull T oldItem, @NonNull T newItem)

Called to check whether two items have the same data.
abstract boolean
areItemsTheSame(@NonNull T oldItem, @NonNull T newItem)

Called to check whether two objects represent the same item.
@Nullable Object
getChangePayload(@NonNull T oldItem, @NonNull T newItem)

When areItemsTheSame returns true for two items and areContentsTheSame returns false for them, this method is called to get a payload about the change.

Public constructors

ItemCallback

Added in 1.0.0
public ItemCallback()

Public methods

areContentsTheSame

Added in 1.0.0
public abstract boolean areContentsTheSame(@NonNull T oldItem, @NonNull T newItem)

Called to check whether two items have the same data.

This information is used to detect if the contents of an item have changed.

This method to check equality instead of equals 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 returns true for these items.

Note: Two null items are assumed to represent the same contents. This callback will not be invoked for this case.

Parameters
@NonNull T oldItem

The item in the old list.
@NonNull T newItem

The item in the new list.
Returns
boolean

True if the contents of the items are the same or false if they are different.
See also
areContentsTheSame

areItemsTheSame

Added in 1.0.0
public abstract boolean areItemsTheSame(@NonNull T oldItem, @NonNull T newItem)

Called to check whether two objects represent the same item.

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

Note: null items in the list are assumed to be the same as another null item and are assumed to not be the same as a non-null item. This callback will not be invoked for either of those cases.

Parameters
@NonNull T oldItem

The item in the old list.
@NonNull T newItem

The item in the new list.
Returns
boolean

True if the two items represent the same object or false if they are different.
See also
areItemsTheSame

getChangePayload

Added in 1.0.0
public @Nullable Object getChangePayload(@NonNull T oldItem, @NonNull T newItem)

When areItemsTheSame returns true for two items and areContentsTheSame returns false for them, this method is called 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.

See also
getChangePayload