State
open class State
| kotlin.Any | |
| ↳ | androidx.recyclerview.widget.RecyclerView.State |
Contains useful information about the current RecyclerView state like target scroll position or view focus. State object can also keep arbitrary data, identified by resource ids.
Often times, RecyclerView components will need to pass information between each other. To provide a well defined data bus between components, RecyclerView passes the same State object to component callbacks and these components can use it to exchange data.
If you implement custom components, you can use State's put/get/remove methods to pass data between your components without needing to manage their lifecycles.
Summary
| Public constructors | |
|---|---|
<init>()Contains useful information about the current RecyclerView state like target scroll position or view focus. |
|
| Public methods | |
|---|---|
| open Boolean | |
| open T |
Gets the Object mapped from the specified id, or |
| open Int |
Returns the total number of items that can be laid out. |
| open Int |
Returns remaining horizontal scroll distance of an ongoing scroll animation(fling/ smoothScrollTo/SmoothScroller) in pixels. |
| open Int |
Returns remaining vertical scroll distance of an ongoing scroll animation(fling/ smoothScrollTo/SmoothScroller) in pixels. |
| open Int |
If scroll is triggered to make a certain item visible, this value will return the adapter index of that item. |
| open Boolean |
Returns if current scroll has a target position. |
| open Boolean |
Returns true if the RecyclerView is currently measuring the layout. |
| open Boolean |
Returns true if the |
| open Unit |
Adds a mapping from the specified id to the specified value, replacing the previous mapping from the specified key if there was one. |
| open Unit |
Removes the mapping from the specified id, if there was any. |
| open String |
toString() |
| open Boolean |
Returns whether RecyclerView will run predictive animations in this layout pass or not. |
| open Boolean |
Returns whether RecyclerView will run simple animations in this layout pass or not. |
Public constructors
<init>
State()
Contains useful information about the current RecyclerView state like target scroll position or view focus. State object can also keep arbitrary data, identified by resource ids.
Often times, RecyclerView components will need to pass information between each other. To provide a well defined data bus between components, RecyclerView passes the same State object to component callbacks and these components can use it to exchange data.
If you implement custom components, you can use State's put/get/remove methods to pass data between your components without needing to manage their lifecycles.
Public methods
didStructureChange
open fun didStructureChange(): Boolean
| Return | |
|---|---|
Boolean |
true if the structure of the data set has changed since the last call to onLayoutChildren, false otherwise |
get
open fun <T : Any!> get(resourceId: Int): T
Gets the Object mapped from the specified id, or null if no such data exists.
| Parameters | |
|---|---|
resourceId |
Int: Id of the resource you want to remove. It is suggested to use R.id.* to preserve cross functionality and avoid conflicts. |
getItemCount
open fun getItemCount(): Int
Returns the total number of items that can be laid out. Note that this number is not necessarily equal to the number of items in the adapter, so you should always use this number for your position calculations and never access the adapter directly.
RecyclerView listens for Adapter's notify events and calculates the effects of adapter data changes on existing Views. These calculations are used to decide which animations should be run.
To support predictive animations, RecyclerView may rewrite or reorder Adapter changes to present the correct state to LayoutManager in pre-layout pass.
For example, a newly added item is not included in pre-layout item count because pre-layout reflects the contents of the adapter before the item is added. Behind the scenes, RecyclerView offsets Recycler#getViewForPosition(int) calls such that LayoutManager does not know about the new item's existence in pre-layout. The item will be available in second layout pass and will be included in the item count. Similar adjustments are made for moved and removed items as well.
You can get the adapter's item count via LayoutManager#getItemCount() method.
| Return | |
|---|---|
Int |
The number of items currently available |
See Also
getRemainingScrollHorizontal
open fun getRemainingScrollHorizontal(): Int
Returns remaining horizontal scroll distance of an ongoing scroll animation(fling/ smoothScrollTo/SmoothScroller) in pixels. Returns zero if getScrollState() is other than SCROLL_STATE_SETTLING.
| Return | |
|---|---|
Int |
Remaining horizontal scroll distance |
getRemainingScrollVertical
open fun getRemainingScrollVertical(): Int
Returns remaining vertical scroll distance of an ongoing scroll animation(fling/ smoothScrollTo/SmoothScroller) in pixels. Returns zero if getScrollState() is other than SCROLL_STATE_SETTLING.
| Return | |
|---|---|
Int |
Remaining vertical scroll distance |
getTargetScrollPosition
open fun getTargetScrollPosition(): Int
If scroll is triggered to make a certain item visible, this value will return the adapter index of that item.
| Return | |
|---|---|
Int |
Adapter index of the target item or RecyclerView#NO_POSITION if there is no target position. |
hasTargetScrollPosition
open fun hasTargetScrollPosition(): Boolean
Returns if current scroll has a target position.
| Return | |
|---|---|
Boolean |
true if scroll is being triggered to make a certain position visible |
See Also
isMeasuring
open fun isMeasuring(): Boolean
Returns true if the RecyclerView is currently measuring the layout. This value is true only if the LayoutManager opted into the auto measure API and RecyclerView has non-exact measurement specs.
Note that if the LayoutManager supports predictive animations and it is calculating the pre-layout step, this value will be false even if the RecyclerView is in onMeasure call. This is because pre-layout means the previous state of the RecyclerView and measurements made for that state cannot change the RecyclerView's size. LayoutManager is always guaranteed to receive another call to LayoutManager#onLayoutChildren(Recycler, State) when this happens.
| Return | |
|---|---|
Boolean |
True if the RecyclerView is currently calculating its bounds, false otherwise. |
isPreLayout
open fun isPreLayout(): Boolean
Returns true if the RecyclerView is in the pre-layout step where it is having its LayoutManager layout items where they will be at the beginning of a set of predictive item animations.
put
open fun put(
resourceId: Int,
data: Any!
): Unit
Adds a mapping from the specified id to the specified value, replacing the previous mapping from the specified key if there was one.
| Parameters | |
|---|---|
resourceId |
Int: Id of the resource you want to add. It is suggested to use R.id.* to preserve cross functionality and avoid conflicts. |
data |
Any!: The data you want to associate with the resourceId. |
remove
open fun remove(resourceId: Int): Unit
Removes the mapping from the specified id, if there was any.
| Parameters | |
|---|---|
resourceId |
Int: Id of the resource you want to remove. It is suggested to use R.id.* to preserve cross functionality and avoid conflicts. |
toString
open fun toString(): String
willRunPredictiveAnimations
open fun willRunPredictiveAnimations(): Boolean
Returns whether RecyclerView will run predictive animations in this layout pass or not.
| Return | |
|---|---|
Boolean |
true if RecyclerView is calculating predictive animations to be run at the end of the layout pass. |