SelectionTracker
abstract class SelectionTracker<K : Any!>
kotlin.Any | |
↳ | androidx.recyclerview.selection.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
.
Summary
Nested classes | |
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Builder is the primary mechanism for create a |
|
abstract |
Observer class providing access to information about Selection state changes. |
abstract |
Implement SelectionPredicate to control when items can be selected or unselected. |
Constants | |
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static String |
This value is included in the payload when SelectionTracker notifies RecyclerView of changes to selection. |
Public constructors | |
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<init>() SelectionTracker provides support for managing a selection of items in a RecyclerView instance. |
Public methods | |
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abstract Unit |
addObserver(@NonNull observer: SelectionTracker.SelectionObserver<K>) Adds |
abstract Boolean |
Clears both primary and provisional selections. |
abstract Unit |
copySelection(@NonNull dest: MutableSelection<K>) Updates |
abstract Boolean |
deselect(@NonNull 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 | |
abstract Boolean |
isSelected(@Nullable key: K?) |
abstract Unit |
onRestoreInstanceState(@Nullable state: Bundle?) Restores selection from previously saved state. |
abstract Unit |
onSaveInstanceState(@NonNull state: Bundle) Preserves selection, if any. |
abstract Boolean |
select(@NonNull key: K) Attempts to select an item. |
abstract Boolean |
setItemsSelected(@NonNull keys: MutableIterable<K>, selected: Boolean) Sets the selected state of the specified items if permitted after consulting SelectionPredicate. |
Protected methods | |
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abstract Unit |
restoreSelection(@NonNull selection: Selection<K>) Restores the selected state of specified items. |
Constants
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"
Public constructors
<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
.
Public methods
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.
Return | |
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Boolean |
true if primary selection changed. |
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.
Return | |
---|---|
Boolean |
true if the item was deselected. False if the item could not be deselected, or was was already un-selected. |
getSelection
@NonNull abstract fun getSelection(): Selection<K>
Returns a Selection object that provides a live view on the current selection.
Return | |
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Selection<K> |
The current selection. |
See Also
isSelected
abstract fun isSelected(@Nullable key: K?): Boolean
Return | |
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Boolean |
true if the item specified by its id is selected. Shorthand for getSelection().contains(K) . |
onRestoreInstanceState
abstract fun onRestoreInstanceState(@Nullable 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(@NonNull 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. |
select
abstract fun select(@NonNull key: K): Boolean
Attempts to select an item.
Return | |
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Boolean |
true if the item was selected. False if the item could not be selected, or was was already selected. |
setItemsSelected
abstract fun setItemsSelected(
@NonNull keys: MutableIterable<K>,
selected: Boolean
): Boolean
Sets the selected state of the specified items if permitted after consulting SelectionPredicate.
Protected methods
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.
Parameters | |
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selection |
Selection<K>: selection being restored. |
See Also