SelectionTracker

public abstract class SelectionTracker<K>

SelectionTracker provides support for managing a selection of items in a RecyclerView instance.

This class provides support for managing a "primary" set of selected items, in addition to a "provisional" set of selected items using conventional java.util.Collections-like methods.

Create an instance of SelectionTracker using SelectionTracker.Builder.

Inspecting the current selection

The underlying selection is described by the Selection class.

A live view of the current selection can be obtained using getSelection. Changes made to the selection using SelectionTracker will be immediately reflected in this instance.

To obtain a stable snapshot of the selection use copySelection.

Selection state for an individual item can be obtained using isSelected.

Provisional Selection

Provisional selection exists to address issues where a transitory selection might momentarily intersect with a previously established selection resulting in a some or all of the established selection being erased. Such situations may arise when band selection is being performed in "additive" mode (e.g. SHIFT or CTRL is pressed on the keyboard prior to mouse down), or when there's an active gesture selection (which can be initiated by long pressing an unselected item while there is an existing selection).

A provisional selection can be abandoned, or merged into the primary selection.

Enforcing selection policies

Which items can be selected by the user is a matter of policy in an Application. Developers supply these policies by way of SelectionPredicate.

Parameters
<K>

Selection key type. @see StorageStrategy for supported types.

Summary

Nested types
public final class SelectionTracker.Builder<K>

Builder is the primary mechanism for create a SelectionTracker that can be used with your RecyclerView.
public abstract class SelectionTracker.SelectionObserver<K>

Observer class providing access to information about Selection state changes.
public abstract class SelectionTracker.SelectionPredicate<K>

Implement SelectionPredicate to control when items can be selected or unselected.

Constants
static final String
SELECTION_CHANGED_MARKER = "Selection-Changed"

This value is included in the payload when SelectionTracker notifies RecyclerView of changes to selection.

Public constructors

Public methods
abstract void

Adds observer to be notified when changes to selection occur.
abstract boolean

Clears both primary and provisional selections.
abstract void

Updates dest to reflect the current selection.
abstract boolean
deselect(@NonNull K key)

Attempts to deselect an item.
abstract @NonNull Selection<K>

Returns a Selection object that provides a live view on the current selection.
abstract boolean
abstract boolean
abstract void

Restores selection from previously saved state.
abstract void

Preserves selection, if any.
abstract boolean
select(@NonNull K key)

Attempts to select an item.
abstract boolean
setItemsSelected(@NonNull Iterable<K> keys, boolean selected)

Sets the selected state of the specified items if permitted after consulting SelectionPredicate.

Protected methods
abstract void

Restores the selected state of specified items.

Constants

SELECTION_CHANGED_MARKER

Added in 1.0.0
public static final String SELECTION_CHANGED_MARKER = "Selection-Changed"

This value is included in the payload when SelectionTracker notifies RecyclerView of changes to selection. Look for this value in the payload Object argument supplied to Adapter#onBindViewHolder. If present the call is occurring in response to a selection state change. This would be a good opportunity to animate changes between unselected and selected state. When state is being restored, this argument will not be present.

Public constructors

SelectionTracker

Added in 1.0.0
public SelectionTracker()

Public methods

addObserver

Added in 1.1.0
public abstract void addObserver(@NonNull SelectionTracker.SelectionObserver<K> observer)

Adds observer to be notified when changes to selection occur.

Use an observer to track attributes about the selection and update the UI to reflect the state of the selection. For example, an author may use an observer to control the enabled status of menu items, or to initiate android.view.ActionMode.

clearSelection

Added in 1.0.0
public abstract boolean clearSelection()

Clears both primary and provisional selections.

Returns
boolean

true if primary selection changed.

copySelection

Added in 1.0.0
public abstract void copySelection(@NonNull MutableSelection<K> dest)

Updates dest to reflect the current selection.

deselect

Added in 1.0.0
public abstract boolean deselect(@NonNull K key)

Attempts to deselect an item.

Returns
boolean

true if the item was deselected. False if the item could not be deselected, or was was already un-selected.

getSelection

Added in 1.0.0
public abstract @NonNull Selection<K> getSelection()

Returns a Selection object that provides a live view on the current selection.

Returns
@NonNull Selection<K>

The current selection.
See also
copySelection

on how to get a snapshot of the selection that will not reflect future changes to selection.

hasSelection

Added in 1.0.0
public abstract boolean hasSelection()
Returns
boolean

true if has a selection

isSelected

Added in 1.0.0
public abstract boolean isSelected(@Nullable K key)
Returns
boolean

true if the item specified by its id is selected. Shorthand for getSelection().contains(K).

onRestoreInstanceState

Added in 1.0.0
public abstract void onRestoreInstanceState(@Nullable Bundle state)

Restores selection from previously saved state. Call this method from Activity#onCreate.

Parameters
@Nullable Bundle state

Bundle instance supplied to onCreate.

onSaveInstanceState

Added in 1.0.0
public abstract void onSaveInstanceState(@NonNull Bundle state)

Preserves selection, if any. Call this method from Activity#onSaveInstanceState

Parameters
@NonNull Bundle state

Bundle instance supplied to onSaveInstanceState.

select

Added in 1.0.0
public abstract boolean select(@NonNull K key)

Attempts to select an item.

Returns
boolean

true if the item was selected. False if the item could not be selected, or was was already selected.

setItemsSelected

Added in 1.0.0
public abstract boolean setItemsSelected(@NonNull Iterable<K> keys, boolean selected)

Sets the selected state of the specified items if permitted after consulting SelectionPredicate.

Protected methods

restoreSelection

Added in 1.0.0
protected abstract void restoreSelection(@NonNull Selection<K> selection)

Restores the selected state of specified items. Used in cases such as restore the selection after rotation etc. Provisional selection is not restored.

This affords clients the ability to restore selection from selection saved in Activity state.

Parameters
@NonNull Selection<K> selection

selection being restored.
See also
StorageStrategy

details on selection state support.