# DiffUtil.Callback

Artifact: [androidx.recyclerview:recyclerview](https://developer.android.com/jetpack/androidx/releases/recyclerview) [View Source](https://cs.android.com/search?q=file:androidx/recyclerview/widget/DiffUtil.java+class:androidx.recyclerview.widget.DiffUtil.Callback) Added in [1.0.0](https://developer.android.com/jetpack/androidx/releases/recyclerview#1.0.0)

*** ** * ** ***


```
public abstract class DiffUtil.Callback
```

<br />

*** ** * ** ***

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

## Summary

| ### Public constructors |
|---|
| `https://developer.android.com/reference/androidx/recyclerview/widget/DiffUtil.Callback#Callback()()` |

| ### Public methods |
|---|---|
| `abstract boolean` | `https://developer.android.com/reference/androidx/recyclerview/widget/DiffUtil.Callback#areContentsTheSame(int,int)(int oldItemPosition, int newItemPosition)` Called by the DiffUtil when it wants to check whether two items have the same data. |
| `abstract boolean` | `https://developer.android.com/reference/androidx/recyclerview/widget/DiffUtil.Callback#areItemsTheSame(int,int)(int oldItemPosition, int newItemPosition)` Called by the DiffUtil to decide whether two object represent the same Item. |
| `@https://developer.android.com/reference/androidx/annotation/Nullable https://developer.android.com/reference/java/lang/Object.html` | `https://developer.android.com/reference/androidx/recyclerview/widget/DiffUtil.Callback#getChangePayload(int,int)(int oldItemPosition, int newItemPosition)` When `https://developer.android.com/reference/androidx/recyclerview/widget/DiffUtil.Callback#areItemsTheSame(int,int)` returns `true` for two items and `https://developer.android.com/reference/androidx/recyclerview/widget/DiffUtil.Callback#areContentsTheSame(int,int)` returns false for them, DiffUtil calls this method to get a payload about the change. |
| `abstract int` | `https://developer.android.com/reference/androidx/recyclerview/widget/DiffUtil.Callback#getNewListSize()()` Returns the size of the new list. |
| `abstract int` | `https://developer.android.com/reference/androidx/recyclerview/widget/DiffUtil.Callback#getOldListSize()()` Returns the size of the old list. |

## Public constructors

### Callback

Added in 1.0.0

```
public Callback()
```

## Public methods

### areContentsTheSame

Added in [1.0.0](https://developer.android.com/jetpack/androidx/releases/recyclerview#1.0.0)

```
public abstract boolean areContentsTheSame(int oldItemPosition, int newItemPosition)
```

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 `https://developer.android.com/reference/java/lang/Object.html#equals(java.lang.Object)` so that you can change its behavior depending on your UI. For example, if you are using DiffUtil with a `https://developer.android.com/reference/androidx/recyclerview/widget/RecyclerView.Adapter`, you should return whether the items' visual representations are the same.

This method is called only if `https://developer.android.com/reference/androidx/recyclerview/widget/DiffUtil.Callback#areItemsTheSame(int,int)` returns `true` for these items.

| Parameters |
|---|---|
| `int oldItemPosition` | The position of the item in the old list |
| `int newItemPosition` | The position of the item in the new list which replaces the oldItem |

| Returns |
|---|---|
| `boolean` | True if the contents of the items are the same or false if they are different. |

### areItemsTheSame

Added in [1.0.0](https://developer.android.com/jetpack/androidx/releases/recyclerview#1.0.0)

```
public abstract boolean areItemsTheSame(int oldItemPosition, int newItemPosition)
```

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 |
|---|---|
| `int oldItemPosition` | The position of the item in the old list |
| `int newItemPosition` | The position of the item in the new list |

| Returns |
|---|---|
| `boolean` | True if the two items represent the same object or false if they are different. |

### getChangePayload

Added in [1.0.0](https://developer.android.com/jetpack/androidx/releases/recyclerview#1.0.0)

```
public @Nullable Object getChangePayload(int oldItemPosition, int newItemPosition)
```

When `https://developer.android.com/reference/androidx/recyclerview/widget/DiffUtil.Callback#areItemsTheSame(int,int)` returns `true` for two items and `https://developer.android.com/reference/androidx/recyclerview/widget/DiffUtil.Callback#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 `https://developer.android.com/reference/androidx/recyclerview/widget/RecyclerView`, you can return the particular field that changed in the item and your `https://developer.android.com/reference/androidx/recyclerview/widget/RecyclerView.ItemAnimator` can use that information to run the correct animation.

Default implementation returns `null`.

| Parameters |
|---|---|
| `int oldItemPosition` | The position of the item in the old list |
| `int newItemPosition` | The position of the item in the new list |

| Returns |
|---|---|
| `@https://developer.android.com/reference/androidx/annotation/Nullable https://developer.android.com/reference/java/lang/Object.html` | A payload object that represents the change between the two items. |

### getNewListSize

Added in [1.0.0](https://developer.android.com/jetpack/androidx/releases/recyclerview#1.0.0)

```
public abstract int getNewListSize()
```

Returns the size of the new list.

| Returns |
|---|---|
| `int` | The size of the new list. |

### getOldListSize

Added in [1.0.0](https://developer.android.com/jetpack/androidx/releases/recyclerview#1.0.0)

```
public abstract int getOldListSize()
```

Returns the size of the old list.

| Returns |
|---|---|
| `int` | The size of the old list. |