public static class RecyclerView.State extends Object
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.
Constructor and Description |
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State() |
Modifier and Type | Method and Description |
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boolean |
didStructureChange() |
<T> T |
get(int resourceId)
Gets the Object mapped from the specified id, or
null
if no such data exists. |
int |
getItemCount()
Returns the total number of items that can be laid out.
|
int |
getTargetScrollPosition()
If scroll is triggered to make a certain item visible, this value will return the
adapter index of that item.
|
boolean |
hasTargetScrollPosition()
Returns if current scroll has a target position.
|
boolean |
isMeasuring()
Returns true if the RecyclerView is currently measuring the layout.
|
boolean |
isPreLayout()
Returns true if
|
void |
put(int resourceId,
Object data)
Adds a mapping from the specified id to the specified value, replacing the previous
mapping from the specified key if there was one.
|
void |
remove(int resourceId)
Removes the mapping from the specified id, if there was any.
|
String |
toString()
Returns a string representation of the object.
|
boolean |
willRunPredictiveAnimations()
Returns whether RecyclerView will run predictive animations in this layout pass
or not.
|
boolean |
willRunSimpleAnimations()
Returns whether RecyclerView will run simple animations in this layout pass
or not.
|
public boolean isMeasuring()
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.
public boolean isPreLayout()
public boolean willRunPredictiveAnimations()
public boolean willRunSimpleAnimations()
public void remove(int resourceId)
resourceId
- Id of the resource you want to remove. It is suggested to use R.id.* to
preserve cross functionality and avoid conflicts.public <T> T get(int resourceId)
null
if no such data exists.resourceId
- Id of the resource you want to remove. It is suggested to use R.id.*
to
preserve cross functionality and avoid conflicts.public void put(int resourceId, Object data)
resourceId
- Id of the resource you want to add. It is suggested to use R.id.* to
preserve cross functionality and avoid conflicts.data
- The data you want to associate with the resourceId.public int getTargetScrollPosition()
RecyclerView.NO_POSITION
if there is no target
position.public boolean hasTargetScrollPosition()
getTargetScrollPosition()
public boolean didStructureChange()
public int getItemCount()
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 RecyclerView.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 RecyclerView.LayoutManager.getItemCount()
method.
RecyclerView.LayoutManager.getItemCount()
public String toString()
Object
toString
method returns a string that
"textually represents" this object. The result should
be a concise but informative representation that is easy for a
person to read.
It is recommended that all subclasses override this method.
The toString
method for class Object
returns a string consisting of the name of the class of which the
object is an instance, the at-sign character `@
', and
the unsigned hexadecimal representation of the hash code of the
object. In other words, this method returns a string equal to the
value of:
getClass().getName() + '@' + Integer.toHexString(hashCode())