Join us on the livestream at Android Dev Summit on 7-8 November 2018, starting at 10AM PDT!

SelectionTracker

public abstract class SelectionTracker
extends Object

java.lang.Object
   ↳ androidx.recyclerview.selection.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 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(MutableSelection).

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

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 SelectionTracker.SelectionPredicate.

Summary

Nested classes

class SelectionTracker.Builder<K>

Builder is the primary mechanism for create a SelectionTracker that can be used with your RecyclerView. 

class SelectionTracker.SelectionObserver<K>

Observer class providing access to information about Selection state changes. 

class SelectionTracker.SelectionPredicate<K>

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

Constants

String SELECTION_CHANGED_MARKER

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

Public constructors

SelectionTracker()

Public methods

abstract void addObserver(SelectionObserver observer)

Adds observer to be notified when changes to selection occur.

abstract boolean clearSelection()

Clears both primary and provisional selections.

abstract void copySelection(MutableSelection<K> dest)

Updates dest to reflect the current selection.

abstract boolean deselect(K key)

Attempts to deselect an item.

abstract Selection<K> getSelection()

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

abstract boolean hasSelection()
abstract boolean isSelected(K key)
abstract void onRestoreInstanceState(Bundle state)

Restores selection from previously saved state.

abstract void onSaveInstanceState(Bundle state)

Preserves selection, if any.

abstract boolean select(K key)

Attempts to select an item.

abstract boolean setItemsSelected(Iterable<K> keys, boolean selected)

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

Protected methods

abstract void restoreSelection(Selection<K> selection)

Restores the selected state of specified items.

Inherited methods

Constants

SELECTION_CHANGED_MARKER

public static final String SELECTION_CHANGED_MARKER

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.

Constant Value: "Selection-Changed"

Public constructors

SelectionTracker

public SelectionTracker ()

Public methods

addObserver

public abstract void addObserver (SelectionObserver 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 ActionMode.

Parameters
observer SelectionObserver

clearSelection

public abstract boolean clearSelection ()

Clears both primary and provisional selections.

Returns
boolean true if primary selection changed.

copySelection

public abstract void copySelection (MutableSelection<K> dest)

Updates dest to reflect the current selection.

Parameters
dest MutableSelection

deselect

public abstract boolean deselect (K key)

Attempts to deselect an item.

Parameters
key K

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

getSelection

public abstract Selection<K> getSelection ()

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

Returns
Selection<K> The current selection.

hasSelection

public abstract boolean hasSelection ()

Returns
boolean true if has a selection

isSelected

public abstract boolean isSelected (K key)

Parameters
key K

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

onRestoreInstanceState

public abstract void onRestoreInstanceState (Bundle state)

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

Parameters
state Bundle: Bundle instance supplied to onCreate.

onSaveInstanceState

public abstract void onSaveInstanceState (Bundle state)

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

Parameters
state Bundle: Bundle instance supplied to onSaveInstanceState.

select

public abstract boolean select (K key)

Attempts to select an item.

Parameters
key K

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

setItemsSelected

public abstract boolean setItemsSelected (Iterable<K> keys, 
                boolean selected)

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

Parameters
keys Iterable

selected boolean

Returns
boolean

Protected methods

restoreSelection

protected abstract void restoreSelection (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
selection Selection: selection being restored.