java.lang.Object | ||
↳ | android.support.v7.widget.RecyclerView.LayoutManager | |
↳ | android.support.v7.widget.LinearLayoutManager |
A RecyclerView.LayoutManager
implementation which provides
similar functionality to ListView
.
Constants | |||||||||||
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int | HORIZONTAL | ||||||||||
int | INVALID_OFFSET | ||||||||||
int | VERTICAL |
Public Constructors | |||||||||||
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Creates a vertical LinearLayoutManager
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Public Methods | |||||||||||
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Query if horizontal scrolling is currently supported.
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Query if vertical scrolling is currently supported.
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Override this method if you want to support scroll bars. | |||||||||||
Override this method if you want to support scroll bars. | |||||||||||
Override this method if you want to support scroll bars. | |||||||||||
Override this method if you want to support scroll bars. | |||||||||||
Override this method if you want to support scroll bars. | |||||||||||
Override this method if you want to support scroll bars. | |||||||||||
Returns the adapter position of the first fully visible view.
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Returns the adapter position of the first visible view.
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Returns the adapter position of the last fully visible view.
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Returns the adapter position of the last visible view.
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Finds the view which represents the given adapter position. | |||||||||||
Create a default
LayoutParams object for a child of the RecyclerView.
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Returns the current orientaion of the layout.
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Returns if views are laid out from the opposite direction of the layout.
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Called when searching for a focusable view in the given direction has failed
for the current content of the RecyclerView.
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Lay out all relevant child views from the given adapter.
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Called when the LayoutManager should save its state. | |||||||||||
Scroll horizontally by dx pixels in screen coordinates and return the distance traveled.
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Scroll the RecyclerView to make the position visible. | |||||||||||
Scroll to the specified adapter position with the given offset from layout start. | |||||||||||
Scroll vertically by dy pixels in screen coordinates and return the distance traveled.
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Sets the orientation of the layout.
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Used to reverse item traversal and layout order.
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Compatibility support for
setStackFromBottom(boolean)
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Smooth scroll to the specified adapter position. | |||||||||||
Returns whether this LayoutManager supports automatic item animations.
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Protected Methods | |||||||||||
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Returns the amount of extra space that should be rendered by LinearLayoutManager. |
[Expand]
Inherited Methods | |||||||||||
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From class
android.support.v7.widget.RecyclerView.LayoutManager
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From class
java.lang.Object
|
Creates a vertical LinearLayoutManager
context | Current context, will be used to access resources. |
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context | Current context, will be used to access resources. |
---|---|
orientation | Layout orientation. Should be HORIZONTAL or VERTICAL . |
reverseLayout | When set to true, renders the layout from end to start. |
Query if horizontal scrolling is currently supported. The default implementation returns false.
getOrientation()
is HORIZONTAL
Query if vertical scrolling is currently supported. The default implementation returns false.
getOrientation()
is VERTICAL
Override this method if you want to support scroll bars.
Read computeHorizontalScrollExtent()
for details.
Default implementation returns 0.
state | Current state of RecyclerView |
---|
Override this method if you want to support scroll bars.
Read computeHorizontalScrollOffset()
for details.
Default implementation returns 0.
state | Current State of RecyclerView where you can find total item count |
---|
Override this method if you want to support scroll bars.
Read computeHorizontalScrollRange()
for details.
Default implementation returns 0.
state | Current State of RecyclerView where you can find total item count |
---|
Override this method if you want to support scroll bars.
Read computeVerticalScrollExtent()
for details.
Default implementation returns 0.
state | Current state of RecyclerView |
---|
Override this method if you want to support scroll bars.
Read computeVerticalScrollOffset()
for details.
Default implementation returns 0.
state | Current State of RecyclerView where you can find total item count |
---|
Override this method if you want to support scroll bars.
Read computeVerticalScrollRange()
for details.
Default implementation returns 0.
state | Current State of RecyclerView where you can find total item count |
---|
Returns the adapter position of the first fully visible view.
Note that bounds check is only performed in the current orientation. That means, if LinearLayoutManager is horizontal, it will only check the view's left and right edges.
NO_POSITION
if there aren't any visible items.Returns the adapter position of the first visible view.
Note that, this value is not affected by layout orientation or item order traversal.
(setReverseLayout(boolean)
). Views are sorted by their positions in the adapter,
not in the layout.
If RecyclerView has item decorators, they will be considered in calculations as well.
LinearLayoutManager may pre-cache some views that are not necessarily visible. Those views are ignored in this method.
NO_POSITION
if
there aren't any visible items.Returns the adapter position of the last fully visible view.
Note that bounds check is only performed in the current orientation. That means, if LinearLayoutManager is horizontal, it will only check the view's left and right edges.
NO_POSITION
if there aren't any visible items.Returns the adapter position of the last visible view.
Note that, this value is not affected by layout orientation or item order traversal.
(setReverseLayout(boolean)
). Views are sorted by their positions in the adapter,
not in the layout.
If RecyclerView has item decorators, they will be considered in calculations as well.
LinearLayoutManager may pre-cache some views that are not necessarily visible. Those views are ignored in this method.
NO_POSITION
if
there aren't any visible items.Finds the view which represents the given adapter position.
This method traverses each child since it has no information about child order. Override this method to improve performance if your LayoutManager keeps data about child views.
position | Position of the item in adapter |
---|
Create a default LayoutParams
object for a child of the RecyclerView.
LayoutManagers will often want to use a custom LayoutParams
type
to store extra information specific to the layout. Client code should subclass
RecyclerView.LayoutParams
for this purpose.
Important: if you use your own custom LayoutParams
type
you must also override
checkLayoutParams(LayoutParams)
,
generateLayoutParams(android.view.ViewGroup.LayoutParams)
and
generateLayoutParams(android.content.Context, android.util.AttributeSet)
.
Returns the current orientaion of the layout.
Returns if views are laid out from the opposite direction of the layout.
Called when searching for a focusable view in the given direction has failed for the current content of the RecyclerView.
This is the LayoutManager's opportunity to populate views in the given direction to fulfill the request if it can. The LayoutManager should attach and return the view to be focused. The default implementation returns null.
focused | The currently focused view |
---|---|
focusDirection | One of FOCUS_UP , FOCUS_DOWN ,
FOCUS_LEFT , FOCUS_RIGHT ,
FOCUS_BACKWARD , FOCUS_FORWARD
or 0 for not applicable |
recycler | The recycler to use for obtaining views for currently offscreen items |
state | Transient state of RecyclerView |
Lay out all relevant child views from the given adapter.
The LayoutManager is in charge of the behavior of item animations. By default,
RecyclerView has a non-null ItemAnimator
, and simple
item animations are enabled. This means that add/remove operations on the
adapter will result in animations to add new or appearing items, removed or
disappearing items, and moved items. If a LayoutManager returns false from
supportsPredictiveItemAnimations()
, which is the default, and runs a
normal layout operation during onLayoutChildren(Recycler, State)
, the
RecyclerView will have enough information to run those animations in a simple
way. For example, the default ItemAnimator, DefaultItemAnimator
, will
simple fade views in and out, whether they are actuall added/removed or whether
they are moved on or off the screen due to other add/remove operations.
A LayoutManager wanting a better item animation experience, where items can be
animated onto and off of the screen according to where the items exist when they
are not on screen, then the LayoutManager should return true from
supportsPredictiveItemAnimations()
and add additional logic to
onLayoutChildren(Recycler, State)
. Supporting predictive animations
means that onLayoutChildren(Recycler, State)
will be called twice;
once as a "pre" layout step to determine where items would have been prior to
a real layout, and again to do the "real" layout. In the pre-layout phase,
items will remember their pre-layout positions to allow them to be laid out
appropriately. Also, removed
items will
be returned from the scrap to help determine correct placement of other items.
These removed items should not be added to the child list, but should be used
to help calculate correct positioning of other views, including views that
were not previously onscreen (referred to as APPEARING views), but whose
pre-layout offscreen position can be determined given the extra
information about the pre-layout removed views.
The second layout pass is the real layout in which only non-removed views
will be used. The only additional requirement during this pass is, if
supportsPredictiveItemAnimations()
returns true, to note which
views exist in the child list prior to layout and which are not there after
layout (referred to as DISAPPEARING views), and to position/layout those views
appropriately, without regard to the actual bounds of the RecyclerView. This allows
the animation system to know the location to which to animate these disappearing
views.
The default LayoutManager implementations for RecyclerView handle all of these requirements for animations already. Clients of RecyclerView can either use one of these layout managers directly or look at their implementations of onLayoutChildren() to see how they account for the APPEARING and DISAPPEARING views.
recycler | Recycler to use for fetching potentially cached views for a position |
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state | Transient state of RecyclerView |
Called when the LayoutManager should save its state. This is a good time to save your scroll position, configuration and anything else that may be required to restore the same layout state if the LayoutManager is recreated.
RecyclerView does NOT verify if the LayoutManager has changed between state save and restore. This will let you share information between your LayoutManagers but it is also your responsibility to make sure they use the same parcelable class.
Scroll horizontally by dx pixels in screen coordinates and return the distance traveled. The default implementation does nothing and returns 0.
dx | distance to scroll by in pixels. X increases as scroll position approaches the right. |
---|---|
recycler | Recycler to use for fetching potentially cached views for a position |
state | Transient state of RecyclerView |
Math.abs(result)
may be less than dx if a boundary was reached.
Scroll the RecyclerView to make the position visible.
RecyclerView will scroll the minimum amount that is necessary to make the
target position visible. If you are looking for a similar behavior to
setSelection(int)
or
setSelectionFromTop(int, int)
, use
scrollToPositionWithOffset(int, int)
.
Note that scroll position change will not be reflected until the next layout call.
position | Scroll to this adapter position |
---|
Scroll to the specified adapter position with the given offset from layout start.
Note that scroll position change will not be reflected until the next layout call.
If you are just trying to make a position visible, use scrollToPosition(int)
.
position | Index (starting at 0) of the reference item. |
---|---|
offset | The distance (in pixels) between the start edge of the item view and start edge of the RecyclerView. |
Scroll vertically by dy pixels in screen coordinates and return the distance traveled. The default implementation does nothing and returns 0.
dy | distance to scroll in pixels. Y increases as scroll position approaches the bottom. |
---|---|
recycler | Recycler to use for fetching potentially cached views for a position |
state | Transient state of RecyclerView |
Math.abs(result)
may be less than dy if a boundary was reached.
Sets the orientation of the layout. LinearLayoutManager
will do its best to keep scroll position.
orientation | HORIZONTAL or VERTICAL
|
---|
Used to reverse item traversal and layout order.
This behaves similar to the layout change for RTL views. When set to true, first item is
rendered at the end of the UI, second item is render before it etc.
For horizontal layouts, it depends on the layout direction.
When set to true, If RecyclerView
is LTR, than it will
render from RTL, if RecyclerView
} is RTL, it will render
from LTR.
If you are looking for the exact same behavior of
setStackFromBottom(boolean)
, use
setStackFromEnd(boolean)
Compatibility support for setStackFromBottom(boolean)
Smooth scroll to the specified adapter position.
To support smooth scrolling, override this method, create your RecyclerView.SmoothScroller
instance and call startSmoothScroll(SmoothScroller)
.
recyclerView | The RecyclerView to which this layout manager is attached |
---|---|
state | Current State of RecyclerView |
position | Scroll to this adapter position. |
Returns whether this LayoutManager supports automatic item animations.
A LayoutManager wishing to support item animations should obey certain
rules as outlined in onLayoutChildren(Recycler, State)
.
The default return value is false
, so subclasses of LayoutManager
will not get predictive item animations by default.
Whether item animations are enabled in a RecyclerView is determined both
by the return value from this method and the
ItemAnimator
set on the
RecyclerView itself. If the RecyclerView has a non-null ItemAnimator but this
method returns false, then simple item animations will be enabled, in which
views that are moving onto or off of the screen are simply faded in/out. If
the RecyclerView has a non-null ItemAnimator and this method returns true,
then there will be two calls to onLayoutChildren(Recycler, State)
to
setup up the information needed to more intelligently predict where appearing
and disappearing views should be animated from/to.
Returns the amount of extra space that should be rendered by LinearLayoutManager.
By default, LinearLayoutManager
lays out 1 extra page of
items while smooth scrolling and 0 otherwise. You can override this method to implement your
custom layout pre-cache logic.
Laying out invisible elements will eventually come with performance cost. On the other hand, in places like smooth scrolling to an unknown location, this extra content helps LayoutManager to calculate a much smoother scrolling; which improves user experience.
You can also use this if you are trying to pre-render your upcoming views.