LoadStateAdapter

public abstract class LoadStateAdapter<VH extends RecyclerView.ViewHolder> extends RecyclerView.Adapter

java.lang.Object
   ↳ androidx.recyclerview.widget.RecyclerView.Adapter
     ↳ androidx.paging.LoadStateAdapter

Adapter for displaying a RecyclerView item based on LoadState, such as a loading spinner, or a retry error button.

By default will use one shared view type for all items.

By default, both LoadState.Loading and LoadState.Error are presented as adapter items, other states are not. To configure this, override displayLoadStateAsItem.

To present this Adapter as a header and or footer alongside your PagingDataAdapter, see PagingDataAdapter.withLoadStateHeaderAndFooter, or use ConcatAdapter directly to concatenate Adapters.

import androidx.paging.LoadState
import androidx.paging.LoadStateAdapter
import androidx.recyclerview.widget.RecyclerView

class LoadStateViewHolder(
    parent: ViewGroup,
    retry: () -> Unit
) : RecyclerView.ViewHolder(
    LayoutInflater.from(parent.context)
        .inflate(R.layout.load_state_item, parent, false)
) {
    private val progressBar: ProgressBar = itemView.findViewById(R.id.progress_bar)
    private val errorMsg: TextView = itemView.findViewById(R.id.error_msg)
    private val retry: Button = itemView.findViewById<Button>(R.id.retry_button)
        .also { it.setOnClickListener { retry.invoke() } }

    fun bind(loadState: LoadState) {
        if (loadState is LoadState.Error) {
            errorMsg.text = loadState.error.localizedMessage
        }
        progressBar.visibility = toVisibility(loadState is LoadState.Loading)
        retry.visibility = toVisibility(loadState !is LoadState.Loading)
        errorMsg.visibility = toVisibility(loadState !is LoadState.Loading)
    }

    private fun toVisibility(constraint: Boolean): Int = if (constraint) {
        View.VISIBLE
    } else {
        View.GONE
    }
}

/**
 * Adapter which displays a loading spinner when `state = LoadState.Loading`, and an error
 * message and retry button when `state is LoadState.Error`.
 */
class MyLoadStateAdapter(
    private val retry: () -> Unit
) : LoadStateAdapter<LoadStateViewHolder>() {

    override fun onCreateViewHolder(parent: ViewGroup, loadState: LoadState) =
        LoadStateViewHolder(parent, retry)

    override fun onBindViewHolder(holder: LoadStateViewHolder, loadState: LoadState) =
        holder.bind(loadState)
}
See also
withLoadStateHeaderAndFooter
withLoadStateHeader
withLoadStateFooter

Summary

Public constructors

Public methods
boolean

Returns true if the LoadState should be displayed as a list item when active.
final int

Returns the total number of items in the data set held by the adapter.
final int
getItemViewType(int position)

Return the view type of the item at position for the purposes of view recycling.
final @NonNull LoadState

LoadState to present in the adapter.
int

Override this method to use different view types per LoadState.
abstract void
onBindViewHolder(@NonNull VH holder, @NonNull LoadState loadState)

Called to bind the passed LoadState to the ViewHolder.
final void
onBindViewHolder(@NonNull VH holder, int position)

Called by RecyclerView to display the data at the specified position.
abstract @NonNull VH

Called to create a ViewHolder for the given LoadState.
final @NonNull VH
onCreateViewHolder(@NonNull ViewGroup parent, int viewType)

Called when RecyclerView needs a new ViewHolder of the given type to represent an item.
final void

LoadState to present in the adapter.

Inherited methods
From androidx.recyclerview.widget.RecyclerView.Adapter
final void
bindViewHolder(@NonNull VH holder, int position)

This method internally calls onBindViewHolder to update the ViewHolder contents with the item at the given position and also sets up some private fields to be used by RecyclerView.
final @NonNull VH
createViewHolder(@NonNull ViewGroup parent, int viewType)

This method calls onCreateViewHolder to create a new ViewHolder and initializes some private fields to be used by RecyclerView.
int

Returns the position of the given ViewHolder in the given Adapter.
long
getItemId(int position)

Return the stable ID for the item at position.
final @NonNull RecyclerView.Adapter.StateRestorationPolicy

Returns when this Adapter wants to restore the state.
final boolean

Returns true if one or more observers are attached to this adapter.
final boolean

Returns true if this adapter publishes a unique long value that can act as a key for the item at a given position in the data set.
final void

Notify any registered observers that the data set has changed.
final void
notifyItemChanged(int position)

Notify any registered observers that the item at position has changed.
final void
notifyItemChanged(int position, @Nullable Object payload)

Notify any registered observers that the item at position has changed with an optional payload object.
final void
notifyItemInserted(int position)

Notify any registered observers that the item reflected at position has been newly inserted.
final void
notifyItemMoved(int fromPosition, int toPosition)

Notify any registered observers that the item reflected at fromPosition has been moved to toPosition.
final void
notifyItemRangeChanged(int positionStart, int itemCount)

Notify any registered observers that the itemCount items starting at position positionStart have changed.
final void
notifyItemRangeChanged(
    int positionStart,
    int itemCount,
    @Nullable Object payload
)

Notify any registered observers that the itemCount items starting at position positionStart have changed.
final void
notifyItemRangeInserted(int positionStart, int itemCount)

Notify any registered observers that the currently reflected itemCount items starting at positionStart have been newly inserted.
final void
notifyItemRangeRemoved(int positionStart, int itemCount)

Notify any registered observers that the itemCount items previously located at positionStart have been removed from the data set.
final void
notifyItemRemoved(int position)

Notify any registered observers that the item previously located at position has been removed from the data set.
void

Called by RecyclerView when it starts observing this Adapter.
void
onBindViewHolder(
    @NonNull VH holder,
    int position,
    @NonNull List<@NonNull Object> payloads
)

Called by RecyclerView to display the data at the specified position.
void

Called by RecyclerView when it stops observing this Adapter.
boolean

Called by the RecyclerView if a ViewHolder created by this Adapter cannot be recycled due to its transient state.
void

Called when a view created by this adapter has been attached to a window.
void

Called when a view created by this adapter has been detached from its window.
void
onViewRecycled(@NonNull VH holder)

Called when a view created by this adapter has been recycled.
void

Register a new observer to listen for data changes.
void
setHasStableIds(boolean hasStableIds)

Indicates whether each item in the data set can be represented with a unique identifier of type java.lang.Long.
void

Sets the state restoration strategy for the Adapter.
void

Unregister an observer currently listening for data changes.

Public constructors

LoadStateAdapter

public <VH extends RecyclerView.ViewHolder> LoadStateAdapter()

Public methods

displayLoadStateAsItem

Added in 3.0.0
public boolean displayLoadStateAsItem(@NonNull LoadState loadState)

Returns true if the LoadState should be displayed as a list item when active.

By default, LoadState.Loading and LoadState.Error present as list items, others do not.

getItemCount

Added in 3.0.0
public final int getItemCount()

Returns the total number of items in the data set held by the adapter.

Returns
int

The total number of items in this adapter.

getItemViewType

Added in 3.0.0
public final int getItemViewType(int position)

Return the view type of the item at position for the purposes of view recycling.

The default implementation of this method returns 0, making the assumption of a single view type for the adapter. Unlike ListView adapters, types need not be contiguous. Consider using id resources to uniquely identify item view types.

Parameters
int position

position to query
Returns
int

integer value identifying the type of the view needed to represent the item at position. Type codes need not be contiguous.

getLoadState

Added in 3.0.0
public final @NonNull LoadState getLoadState()

LoadState to present in the adapter.

Changing this property will immediately notify the Adapter to change the item it's presenting.

getStateViewType

Added in 3.0.0
public int getStateViewType(@NonNull LoadState loadState)

Override this method to use different view types per LoadState.

By default, this LoadStateAdapter only uses a single view type.

onBindViewHolder

Added in 3.0.0
public abstract void onBindViewHolder(@NonNull VH holder, @NonNull LoadState loadState)

Called to bind the passed LoadState to the ViewHolder.

Parameters
@NonNull LoadState loadState

LoadState to display.
See also
getItemViewType
displayLoadStateAsItem

onBindViewHolder

Added in 3.0.0
public final void onBindViewHolder(@NonNull VH holder, int position)

Called by RecyclerView to display the data at the specified position. This method should update the contents of the itemView to reflect the item at the given position.

Note that unlike android.widget.ListView, RecyclerView will not call this method again if the position of the item changes in the data set unless the item itself is invalidated or the new position cannot be determined. For this reason, you should only use the position parameter while acquiring the related data item inside this method and should not keep a copy of it. If you need the position of an item later on (e.g. in a click listener), use getBindingAdapterPosition which will have the updated adapter position. Override onBindViewHolder instead if Adapter can handle efficient partial bind.

Parameters
@NonNull VH holder

The ViewHolder which should be updated to represent the contents of the item at the given position in the data set.
int position

The position of the item within the adapter's data set.

onCreateViewHolder

Added in 3.0.0
public abstract @NonNull VH onCreateViewHolder(@NonNull ViewGroup parent, @NonNull LoadState loadState)

Called to create a ViewHolder for the given LoadState.

Parameters
@NonNull ViewGroup parent

The ViewGroup into which the new View will be added after it is bound to an adapter position.
@NonNull LoadState loadState

The LoadState to be initially presented by the new ViewHolder.
See also
getItemViewType
displayLoadStateAsItem

onCreateViewHolder

Added in 3.0.0
public final @NonNull VH onCreateViewHolder(@NonNull ViewGroup parent, int viewType)

Called when RecyclerView needs a new ViewHolder of the given type to represent an item.

This new ViewHolder should be constructed with a new View that can represent the items of the given type. You can either create a new View manually or inflate it from an XML layout file.

The new ViewHolder will be used to display items of the adapter using onBindViewHolder. Since it will be re-used to display different items in the data set, it is a good idea to cache references to sub views of the View to avoid unnecessary findViewById calls.

Parameters
@NonNull ViewGroup parent

The ViewGroup into which the new View will be added after it is bound to an adapter position.
int viewType

The view type of the new View.
Returns
@NonNull VH

A new ViewHolder that holds a View of the given view type.
See also
getItemViewType
onBindViewHolder

setLoadState

Added in 3.0.0
public final void setLoadState(@NonNull LoadState loadState)

LoadState to present in the adapter.

Changing this property will immediately notify the Adapter to change the item it's presenting.