SelectionTracker
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 | |
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<K> |
Selection key type. @see |
Summary
Nested types |
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class SelectionTracker.Builder<K>Builder is the primary mechanism for create a |
abstract class SelectionTracker.SelectionObserver<K>Observer class providing access to information about Selection state changes. |
abstract class SelectionTracker.SelectionPredicate<K>Implement SelectionPredicate to control when items can be selected or unselected. |
Constants |
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const String! |
SELECTION_CHANGED_MARKER = "Selection-Changed"This value is included in the payload when SelectionTracker notifies RecyclerView of changes to selection. |
Public constructors |
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Public functions |
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abstract Unit |
addObserver(observer: SelectionTracker.SelectionObserver<K!>)Adds |
abstract Boolean |
Clears both primary and provisional selections. |
abstract Unit |
copySelection(dest: MutableSelection<K!>)Updates |
abstract Boolean |
deselect(key: K)Attempts to deselect an item. |
abstract Selection<K!> |
Returns a Selection object that provides a live view on the current selection. |
abstract Boolean |
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abstract Boolean |
isSelected(key: K?) |
abstract Unit |
onRestoreInstanceState(state: Bundle?)Restores selection from previously saved state. |
abstract Unit |
onSaveInstanceState(state: Bundle)Preserves selection, if any. |
abstract Boolean |
select(key: K)Attempts to select an item. |
abstract Boolean |
setItemsSelected(keys: (Mutable)Iterable<K!>, selected: Boolean)Sets the selected state of the specified items if permitted after consulting SelectionPredicate. |
Protected functions |
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abstract Unit |
restoreSelection(selection: Selection<K!>)Restores the selected state of specified items. |
Constants
SELECTION_CHANGED_MARKER
const val SELECTION_CHANGED_MARKER = "Selection-Changed": 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 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
Public functions
addObserver
abstract fun addObserver(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.
| Returns | |
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Boolean |
true if primary selection changed. |
copySelection
abstract fun copySelection(dest: MutableSelection<K!>): Unit
Updates dest to reflect the current selection.
deselect
abstract fun deselect(key: K): Boolean
Attempts to deselect an item.
| Returns | |
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Boolean |
true if the item was deselected. False if the item could not be deselected, or was was already un-selected. |
getSelection
abstract fun getSelection(): Selection<K!>
Returns a Selection object that provides a live view on the current selection.
| Returns | |
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Selection<K!> |
The current selection. |
| See also | |
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copySelection |
on how to get a snapshot of the selection that will not reflect future changes to selection. |
hasSelection
abstract fun hasSelection(): Boolean
| Returns | |
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Boolean |
true if has a selection |
isSelected
abstract fun isSelected(key: K?): Boolean
| Returns | |
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Boolean |
true if the item specified by its id is selected. Shorthand for |
onRestoreInstanceState
abstract fun onRestoreInstanceState(state: Bundle?): Unit
Restores selection from previously saved state. Call this method from Activity#onCreate.
| Parameters | |
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state: Bundle? |
Bundle instance supplied to onCreate. |
onSaveInstanceState
abstract fun onSaveInstanceState(state: Bundle): Unit
Preserves selection, if any. Call this method from Activity#onSaveInstanceState
| Parameters | |
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state: Bundle |
Bundle instance supplied to onSaveInstanceState. |
Protected functions
restoreSelection
protected abstract fun restoreSelection(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.
| Parameters | |
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selection: Selection<K!> |
selection being restored. |
| See also | |
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StorageStrategy |
details on selection state support. |