# PagingDataPresenter

Artifact: [androidx.paging:paging-common](https://developer.android.com/jetpack/androidx/releases/paging) [View Source](https://cs.android.com/search?q=file:androidx/paging/PagingDataPresenter.kt+class:androidx.paging.PagingDataPresenter) Added in [3.3.0](https://developer.android.com/jetpack/androidx/releases/paging#3.3.0)

*** ** * ** ***


```
public abstract class PagingDataPresenter<T extends Object>
```

<br />

*** ** * ** ***

The class that connects the UI layer to the underlying Paging operations. Takes input from UI presenters and outputs Paging events (Loads, LoadStateUpdate) in response.

Paging front ends that implement this class will be able to access loaded data, LoadStates, and callbacks from LoadState or Page updates. This class also exposes the `https://developer.android.com/reference/androidx/paging/PagingDataEvent` from a `https://developer.android.com/reference/androidx/paging/PagingData` for custom logic on how to present Loads, Drops, and other Paging events.

For implementation examples, refer to AsyncPagingDataDiffer for RecyclerView, or `https://developer.android.com/reference/kotlin/androidx/paging/compose/LazyPagingItems.html` for Compose.

## Summary

| ### Public constructors |
|---|
| `<T extends https://developer.android.com/reference/java/lang/Object.html> https://developer.android.com/reference/androidx/paging/PagingDataPresenter#PagingDataPresenter(kotlin.coroutines.CoroutineContext,androidx.paging.PagingData)( @https://developer.android.com/reference/androidx/annotation/NonNull https://kotlinlang.org/api/core/kotlin-stdlib/kotlin.coroutines/-coroutine-context/index.html mainContext, https://developer.android.com/reference/androidx/paging/PagingData<@https://developer.android.com/reference/androidx/annotation/NonNull T> cachedPagingData )` |

| ### Public methods |
|---|---|
| `final void` | `https://developer.android.com/reference/androidx/paging/PagingDataPresenter#addLoadStateListener(kotlin.Function1)( @https://developer.android.com/reference/androidx/annotation/NonNull Function1<@https://developer.android.com/reference/androidx/annotation/NonNull https://developer.android.com/reference/androidx/paging/CombinedLoadStates, https://kotlinlang.org/api/core/kotlin-stdlib/kotlin/-unit/index.html> listener )` Add a `https://developer.android.com/reference/androidx/paging/CombinedLoadStates` listener to observe the loading state of the current `https://developer.android.com/reference/androidx/paging/PagingData`. |
| `final void` | `https://developer.android.com/reference/androidx/paging/PagingDataPresenter#addOnPagesUpdatedListener(kotlin.Function0)(@https://developer.android.com/reference/androidx/annotation/NonNull Function0<https://kotlinlang.org/api/core/kotlin-stdlib/kotlin/-unit/index.html> listener)` Add a listener which triggers after the pages presented to the UI are updated, even if the actual items presented don't change. |
| `final void` | `https://developer.android.com/reference/androidx/paging/PagingDataPresenter#collectFrom(androidx.paging.PagingData)(@https://developer.android.com/reference/androidx/annotation/NonNull https://developer.android.com/reference/androidx/paging/PagingData<@https://developer.android.com/reference/androidx/annotation/NonNull T> pagingData)` |
| `final T` | `@https://developer.android.com/reference/androidx/annotation/MainThread https://developer.android.com/reference/androidx/paging/PagingDataPresenter#get(kotlin.Int)(@https://developer.android.com/reference/androidx/annotation/IntRange(from = 0) int index)` Returns the presented item at the specified position, notifying Paging of the item access to trigger any loads necessary to fulfill `https://developer.android.com/reference/androidx/paging/PagingConfig#prefetchDistance()`. |
| `final @https://developer.android.com/reference/androidx/annotation/NonNull https://kotlinlang.org/api/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines.flow/-state-flow/index.html<https://developer.android.com/reference/androidx/paging/CombinedLoadStates>` | `https://developer.android.com/reference/androidx/paging/PagingDataPresenter#getLoadStateFlow()()` A hot `https://kotlinlang.org/api/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines.flow/-flow/index.html` of `https://developer.android.com/reference/androidx/paging/CombinedLoadStates` that emits a snapshot whenever the loading state of the current `https://developer.android.com/reference/androidx/paging/PagingData` changes. |
| `final @https://developer.android.com/reference/androidx/annotation/NonNull https://kotlinlang.org/api/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines.flow/-flow/index.html<https://kotlinlang.org/api/core/kotlin-stdlib/kotlin/-unit/index.html>` | `https://developer.android.com/reference/androidx/paging/PagingDataPresenter#getOnPagesUpdatedFlow()()` A hot `https://kotlinlang.org/api/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines.flow/-flow/index.html` that emits after the pages presented to the UI are updated, even if the actual items presented don't change. |
| `final int` | `https://developer.android.com/reference/androidx/paging/PagingDataPresenter#getSize()()` |
| `final T` | `@https://developer.android.com/reference/androidx/annotation/MainThread https://developer.android.com/reference/androidx/paging/PagingDataPresenter#peek(kotlin.Int)(@https://developer.android.com/reference/androidx/annotation/IntRange(from = 0) int index)` Returns the presented item at the specified position, without notifying Paging of the item access that would normally trigger page loads. |
| `abstract void` | `https://developer.android.com/reference/androidx/paging/PagingDataPresenter#presentPagingDataEvent(androidx.paging.PagingDataEvent)(@https://developer.android.com/reference/androidx/annotation/NonNull https://developer.android.com/reference/androidx/paging/PagingDataEvent<@https://developer.android.com/reference/androidx/annotation/NonNull T> event)` Handler for `https://developer.android.com/reference/androidx/paging/PagingDataEvent` emitted by `https://developer.android.com/reference/androidx/paging/PagingData`. |
| `final void` | `https://developer.android.com/reference/androidx/paging/PagingDataPresenter#refresh()()` Refresh the data presented by this `https://developer.android.com/reference/androidx/paging/PagingDataPresenter`. |
| `final void` | `https://developer.android.com/reference/androidx/paging/PagingDataPresenter#removeLoadStateListener(kotlin.Function1)( @https://developer.android.com/reference/androidx/annotation/NonNull Function1<@https://developer.android.com/reference/androidx/annotation/NonNull https://developer.android.com/reference/androidx/paging/CombinedLoadStates, https://kotlinlang.org/api/core/kotlin-stdlib/kotlin/-unit/index.html> listener )` Remove a previously registered `https://developer.android.com/reference/androidx/paging/CombinedLoadStates` listener. |
| `final void` | `https://developer.android.com/reference/androidx/paging/PagingDataPresenter#removeOnPagesUpdatedListener(kotlin.Function0)(@https://developer.android.com/reference/androidx/annotation/NonNull Function0<https://kotlinlang.org/api/core/kotlin-stdlib/kotlin/-unit/index.html> listener)` Remove a previously registered listener for updates to presented pages. |
| `final void` | `https://developer.android.com/reference/androidx/paging/PagingDataPresenter#retry()()` Retry any failed load requests that would result in a `https://developer.android.com/reference/androidx/paging/LoadState.Error` update to this `https://developer.android.com/reference/androidx/paging/PagingDataPresenter`. |
| `final @https://developer.android.com/reference/androidx/annotation/NonNull https://developer.android.com/reference/androidx/paging/ItemSnapshotList<@https://developer.android.com/reference/androidx/annotation/NonNull T>` | `https://developer.android.com/reference/androidx/paging/PagingDataPresenter#snapshot()()` Returns a new `https://developer.android.com/reference/androidx/paging/ItemSnapshotList` representing the currently presented items, including any placeholders if they are enabled. |

## Public constructors

### PagingDataPresenter

```
public <T extends Object> PagingDataPresenter(
    @NonNull CoroutineContext mainContext,
    PagingData<@NonNull T> cachedPagingData
)
```

| Parameters |
|---|---|
| `@https://developer.android.com/reference/androidx/annotation/NonNull https://kotlinlang.org/api/core/kotlin-stdlib/kotlin.coroutines/-coroutine-context/index.html mainContext` | The coroutine context that core Paging operations will run on. Defaults to `https://kotlinlang.org/api/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines/-dispatchers/-main.html`. Main operations executed within this context include but are not limited to: 1. flow collection on a `https://developer.android.com/reference/androidx/paging/PagingData` for Loads, LoadStateUpdate etc. 2. emitting `https://developer.android.com/reference/androidx/paging/CombinedLoadStates` to the `https://developer.android.com/reference/androidx/paging/PagingDataPresenter#loadStateFlow()` 3. invoking LoadState and PageUpdate listeners 4. invoking `https://developer.android.com/reference/androidx/paging/PagingDataPresenter#presentPagingDataEvent(androidx.paging.PagingDataEvent)` |
| `https://developer.android.com/reference/androidx/paging/PagingData<@https://developer.android.com/reference/androidx/annotation/NonNull T> cachedPagingData` | a `https://developer.android.com/reference/androidx/paging/PagingData` that will initialize this PagingDataPresenter with any LoadStates or loaded data contained within it. |

## Public methods

### addLoadStateListener

```
public final void addLoadStateListener(
    @NonNull Function1<@NonNull CombinedLoadStates, Unit> listener
)
```

Add a `https://developer.android.com/reference/androidx/paging/CombinedLoadStates` listener to observe the loading state of the current `https://developer.android.com/reference/androidx/paging/PagingData`.

As new `https://developer.android.com/reference/androidx/paging/PagingData` generations are submitted and displayed, the listener will be notified to reflect the current `https://developer.android.com/reference/androidx/paging/CombinedLoadStates`.

When a new listener is added, it will be immediately called with the current `https://developer.android.com/reference/androidx/paging/CombinedLoadStates`, unless this `https://developer.android.com/reference/androidx/paging/PagingDataPresenter` has not been hooked up to a `https://developer.android.com/reference/androidx/paging/PagingData` yet, and thus has no state to emit.

```kotlin
import androidx.paging.LoadState

val adapter = UserPagingAdapter()
adapter.addLoadStateListener {
    // show a retry button outside the list when refresh hits an error
    retryButton.isVisible = it.refresh is LoadState.Error

    // swipeRefreshLayout displays whether refresh is occurring
    swipeRefreshLayout.isRefreshing = it.refresh is LoadState.Loading

    // show an empty state over the list when loading initially, before items are loaded
    emptyState.isVisible = it.refresh is LoadState.Loading && adapter.itemCount == 0
}
```

| Parameters |
|---|---|
| `@https://developer.android.com/reference/androidx/annotation/NonNull Function1<@https://developer.android.com/reference/androidx/annotation/NonNull https://developer.android.com/reference/androidx/paging/CombinedLoadStates, https://kotlinlang.org/api/core/kotlin-stdlib/kotlin/-unit/index.html> listener` | `https://developer.android.com/reference/androidx/paging/LoadStates` listener to receive updates. |

| See also |
|---|---|
| `https://developer.android.com/reference/androidx/paging/PagingDataPresenter#removeLoadStateListener(kotlin.Function1)` |   |

### addOnPagesUpdatedListener

Added in [3.3.0](https://developer.android.com/jetpack/androidx/releases/paging#3.3.0)

```
public final void addOnPagesUpdatedListener(@NonNull Function0<Unit> listener)
```

Add a listener which triggers after the pages presented to the UI are updated, even if the actual items presented don't change.

An update is triggered from one of the following:

- `https://developer.android.com/reference/androidx/paging/PagingDataPresenter#collectFrom(androidx.paging.PagingData)` is called and initial load completes, regardless of any differences in the loaded data

- A `https://developer.android.com/reference/androidx/paging/PagingSource.LoadResult.Page` is inserted

- A `https://developer.android.com/reference/androidx/paging/PagingSource.LoadResult.Page` is dropped

| Parameters |
|---|---|
| `@https://developer.android.com/reference/androidx/annotation/NonNull Function0<https://kotlinlang.org/api/core/kotlin-stdlib/kotlin/-unit/index.html> listener` | called after pages presented are updated. |

| See also |
|---|---|
| `https://developer.android.com/reference/androidx/paging/PagingDataPresenter#removeOnPagesUpdatedListener(kotlin.Function0)` |   |

### collectFrom

```
public final void collectFrom(@NonNull PagingData<@NonNull T> pagingData)
```

### get

Added in [3.3.0](https://developer.android.com/jetpack/androidx/releases/paging#3.3.0)

```
@MainThread
public final T get(@IntRange(from = 0) int index)
```

Returns the presented item at the specified position, notifying Paging of the item access to trigger any loads necessary to fulfill `https://developer.android.com/reference/androidx/paging/PagingConfig#prefetchDistance()`.

| Parameters |
|---|---|
| `@https://developer.android.com/reference/androidx/annotation/IntRange(from = 0) int index` | Index of the presented item to return, including placeholders. |

| Returns |
|---|---|
| `T` | The presented item at position `https://developer.android.com/reference/androidx/paging/PagingDataPresenter#get(kotlin.Int)`, `null` if it is a placeholder. |

### getLoadStateFlow

Added in [3.3.0](https://developer.android.com/jetpack/androidx/releases/paging#3.3.0)

```
public final @NonNull StateFlow<CombinedLoadStates> getLoadStateFlow()
```

A hot `https://kotlinlang.org/api/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines.flow/-flow/index.html` of `https://developer.android.com/reference/androidx/paging/CombinedLoadStates` that emits a snapshot whenever the loading state of the current `https://developer.android.com/reference/androidx/paging/PagingData` changes.

This flow is conflated. It buffers the last update to `https://developer.android.com/reference/androidx/paging/CombinedLoadStates` and immediately delivers the current load states on collection, unless this `https://developer.android.com/reference/androidx/paging/PagingDataPresenter` has not been hooked up to a `https://developer.android.com/reference/androidx/paging/PagingData` yet, and thus has no state to emit.

```kotlin
import androidx.lifecycle.lifecycleScope
import androidx.paging.LoadState

val adapter = UserPagingAdapter()
lifecycleScope.launch {
    adapter.loadStateFlow
        .map { it.refresh }
        .distinctUntilChanged()
        .collectLatest {
            // show a retry button outside the list when refresh hits an error
            retryButton.isVisible = it is LoadState.Error

            // swipeRefreshLayout displays whether refresh is occurring
            swipeRefreshLayout.isRefreshing = it is LoadState.Loading

            // show an empty state over the list when loading initially, before items are loaded
            emptyState.isVisible = it is LoadState.Loading && adapter.itemCount == 0
        }
}
```

### getOnPagesUpdatedFlow

Added in [3.3.0](https://developer.android.com/jetpack/androidx/releases/paging#3.3.0)

```
public final @NonNull Flow<Unit> getOnPagesUpdatedFlow()
```

A hot `https://kotlinlang.org/api/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines.flow/-flow/index.html` that emits after the pages presented to the UI are updated, even if the actual items presented don't change.

An update is triggered from one of the following:

- `https://developer.android.com/reference/androidx/paging/PagingDataPresenter#collectFrom(androidx.paging.PagingData)` is called and initial load completes, regardless of any differences in the loaded data

- A `https://developer.android.com/reference/androidx/paging/PagingSource.LoadResult.Page` is inserted

- A `https://developer.android.com/reference/androidx/paging/PagingSource.LoadResult.Page` is dropped

Note: This is a `https://kotlinlang.org/api/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines.flow/-shared-flow/index.html` configured to replay 0 items with a buffer of size 64. If a collector lags behind page updates, it may trigger multiple times for each intermediate update that was presented while your collector was still working. To avoid this behavior, you can `https://kotlinlang.org/api/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines.flow/index.html` this `https://kotlinlang.org/api/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines.flow/-flow/index.html` so that you only receive the latest update, which is useful in cases where you are simply updating UI and don't care about tracking the exact number of page updates.

### getSize

Added in [3.3.0](https://developer.android.com/jetpack/androidx/releases/paging#3.3.0)

```
public final int getSize()
```

| Returns |
|---|---|
| `int` | Total number of presented items, including placeholders. |

### peek

Added in [3.3.0](https://developer.android.com/jetpack/androidx/releases/paging#3.3.0)

```
@MainThread
public final T peek(@IntRange(from = 0) int index)
```

Returns the presented item at the specified position, without notifying Paging of the item access that would normally trigger page loads.

| Parameters |
|---|---|
| `@https://developer.android.com/reference/androidx/annotation/IntRange(from = 0) int index` | Index of the presented item to return, including placeholders. |

| Returns |
|---|---|
| `T` | The presented item at position `https://developer.android.com/reference/androidx/paging/PagingDataPresenter#peek(kotlin.Int)`, `null` if it is a placeholder |

### presentPagingDataEvent

```
public abstract void presentPagingDataEvent(@NonNull PagingDataEvent<@NonNull T> event)
```

Handler for `https://developer.android.com/reference/androidx/paging/PagingDataEvent` emitted by `https://developer.android.com/reference/androidx/paging/PagingData`.

When a `https://developer.android.com/reference/androidx/paging/PagingData` is submitted to this PagingDataPresenter through `https://developer.android.com/reference/androidx/paging/PagingDataPresenter#collectFrom(androidx.paging.PagingData)`, page loads, drops, or LoadStateUpdates will be emitted to presenters as `https://developer.android.com/reference/androidx/paging/PagingDataEvent` through this method.

Presenter layers that communicate directly with `https://developer.android.com/reference/androidx/paging/PagingDataPresenter` should override this method to handle the `https://developer.android.com/reference/androidx/paging/PagingDataEvent` accordingly. For example by diffing two `https://developer.android.com/reference/androidx/paging/PagingDataEvent.Refresh` lists, or appending the inserted list of data from `https://developer.android.com/reference/androidx/paging/PagingDataEvent.Prepend` or `https://developer.android.com/reference/androidx/paging/PagingDataEvent.Append`.

### refresh

Added in [3.3.0](https://developer.android.com/jetpack/androidx/releases/paging#3.3.0)

```
public final void refresh()
```

Refresh the data presented by this `https://developer.android.com/reference/androidx/paging/PagingDataPresenter`.

`https://developer.android.com/reference/androidx/paging/PagingDataPresenter#refresh()` triggers the creation of a new `https://developer.android.com/reference/androidx/paging/PagingData` with a new instance of `https://developer.android.com/reference/androidx/paging/PagingSource` to represent an updated snapshot of the backing dataset. If a `https://developer.android.com/reference/androidx/paging/RemoteMediator` is set, calling `https://developer.android.com/reference/androidx/paging/PagingDataPresenter#refresh()` will also trigger a call to `https://developer.android.com/reference/androidx/paging/RemoteMediator#load(androidx.paging.LoadType,androidx.paging.PagingState)` with `https://developer.android.com/reference/androidx/paging/LoadType#REFRESH` to allow `https://developer.android.com/reference/androidx/paging/RemoteMediator` to check for updates to the dataset backing `https://developer.android.com/reference/androidx/paging/PagingSource`.

Note: This API is intended for UI-driven refresh signals, such as swipe-to-refresh. Invalidation due repository-layer signals, such as DB-updates, should instead use `https://developer.android.com/reference/androidx/paging/PagingSource#invalidate()`.

```kotlin
import androidx.appcompat.app.AppCompatActivity
import androidx.paging.LoadState

class MyActivity : AppCompatActivity() {
    private lateinit var binding: MyActivityBinding
    private val pagingAdapter = UserPagingAdapter()

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        binding = MyActivityBinding.inflate(layoutInflater)
        setContentView(binding.root)

        binding.recyclerView.adapter = pagingAdapter
        pagingAdapter.addLoadStateListener { loadStates ->
            binding.swipeRefreshLayout.isRefreshing = loadStates.refresh is LoadState.Loading
        }

        binding.swipeRefreshLayout.setOnRefreshListener { pagingAdapter.refresh() }
    }
}
```

| See also |
|---|---|
| `https://developer.android.com/reference/androidx/paging/PagingSource#invalidate()` |   |

### removeLoadStateListener

```
public final void removeLoadStateListener(
    @NonNull Function1<@NonNull CombinedLoadStates, Unit> listener
)
```

Remove a previously registered `https://developer.android.com/reference/androidx/paging/CombinedLoadStates` listener.

| Parameters |
|---|---|
| `@https://developer.android.com/reference/androidx/annotation/NonNull Function1<@https://developer.android.com/reference/androidx/annotation/NonNull https://developer.android.com/reference/androidx/paging/CombinedLoadStates, https://kotlinlang.org/api/core/kotlin-stdlib/kotlin/-unit/index.html> listener` | Previously registered listener. |

| See also |
|---|---|
| `https://developer.android.com/reference/androidx/paging/PagingDataPresenter#addLoadStateListener(kotlin.Function1)` |   |

### removeOnPagesUpdatedListener

Added in [3.3.0](https://developer.android.com/jetpack/androidx/releases/paging#3.3.0)

```
public final void removeOnPagesUpdatedListener(@NonNull Function0<Unit> listener)
```

Remove a previously registered listener for updates to presented pages.

| Parameters |
|---|---|
| `@https://developer.android.com/reference/androidx/annotation/NonNull Function0<https://kotlinlang.org/api/core/kotlin-stdlib/kotlin/-unit/index.html> listener` | Previously registered listener. |

| See also |
|---|---|
| `https://developer.android.com/reference/androidx/paging/PagingDataPresenter#addOnPagesUpdatedListener(kotlin.Function0)` |   |

### retry

Added in [3.3.0](https://developer.android.com/jetpack/androidx/releases/paging#3.3.0)

```
public final void retry()
```

Retry any failed load requests that would result in a `https://developer.android.com/reference/androidx/paging/LoadState.Error` update to this `https://developer.android.com/reference/androidx/paging/PagingDataPresenter`.

Unlike `https://developer.android.com/reference/androidx/paging/PagingDataPresenter#refresh()`, this does not invalidate `https://developer.android.com/reference/androidx/paging/PagingSource`, it only retries failed loads within the same generation of `https://developer.android.com/reference/androidx/paging/PagingData`.

`https://developer.android.com/reference/androidx/paging/LoadState.Error` can be generated from two types of load requests:

- `https://developer.android.com/reference/androidx/paging/PagingSource#load(androidx.paging.PagingSource.LoadParams)` returning `https://developer.android.com/reference/androidx/paging/PagingSource.LoadResult.Error`

- `https://developer.android.com/reference/androidx/paging/RemoteMediator#load(androidx.paging.LoadType,androidx.paging.PagingState)` returning `https://developer.android.com/reference/androidx/paging/RemoteMediator.MediatorResult.Error`

### snapshot

Added in [3.3.0](https://developer.android.com/jetpack/androidx/releases/paging#3.3.0)

```
public final @NonNull ItemSnapshotList<@NonNull T> snapshot()
```

Returns a new `https://developer.android.com/reference/androidx/paging/ItemSnapshotList` representing the currently presented items, including any placeholders if they are enabled.