SelectionTracker

SELECTION_CHANGED_MARKER

static val SELECTION_CHANGED_MARKER: String

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 RecyclerView.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.

Value: "Selection-Changed"

<init>

SelectionTracker()

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(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 SelectionPredicate.

addObserver

abstract fun addObserver(@NonNull observer: SelectionTracker.SelectionObserver<K>): Unit

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

abstract fun clearSelection(): Boolean

Clears both primary and provisional selections.

copySelection

abstract fun copySelection(@NonNull dest: MutableSelection<K>): Unit

Updates dest to reflect the current selection.

deselect

abstract fun deselect(@NonNull key: K): Boolean

Attempts to deselect an item.

getSelection

@NonNull abstract fun getSelection(): Selection<K>

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

hasSelection

abstract fun hasSelection(): Boolean

isSelected

abstract fun isSelected(@Nullable key: K?): Boolean

onRestoreInstanceState

abstract fun onRestoreInstanceState(@Nullable state: Bundle?): Unit

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

onSaveInstanceState

abstract fun onSaveInstanceState(@NonNull state: Bundle): Unit

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

select

abstract fun select(@NonNull key: K): Boolean

Attempts to select an item.

setItemsSelected

abstract fun setItemsSelected(
    @NonNull keys: MutableIterable<K>, 
    selected: Boolean
): Boolean

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

restoreSelection

protected abstract fun restoreSelection(@NonNull selection: Selection<K>): Unit

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.