LinearSmoothScroller

Artifact: androidx.recyclerview:recyclerview

Added in 1.0.0

Kotlin |Java

class LinearSmoothScroller : RecyclerView.SmoothScroller

kotlin.Any
↳	androidx.recyclerview.widget.RecyclerView.SmoothScroller
	↳	androidx.recyclerview.widget.LinearSmoothScroller

RecyclerView.SmoothScroller implementation which uses a LinearInterpolator until the target position becomes a child of the RecyclerView and then uses a DecelerateInterpolator to slowly approach to target position.

If the RecyclerView.LayoutManager you are using does not implement the RecyclerView.SmoothScroller.ScrollVectorProvider interface, then you must override the computeScrollVectorForPosition method. All the LayoutManagers bundled with the support library implement this interface.

Summary

Constants
`const Int`	`SNAP_TO_ANY = 0` Decides if the child should be snapped from start or end, depending on where it currently is in relation to its parent.
`const Int`	`SNAP_TO_END = 1` Align child view's right or bottom with parent view's right or bottom
`const Int`	`SNAP_TO_START = -1` Align child view's left or top with parent view's left or top

Public constructors
`LinearSmoothScroller(context: Context!)`

Public functions
`Int`	`calculateDtToFit( viewStart: Int, viewEnd: Int, boxStart: Int, boxEnd: Int, snapPreference: Int )` Helper method for `calculateDxToMakeVisible` and `calculateDyToMakeVisible`
`Int`	`calculateDxToMakeVisible(view: View!, snapPreference: Int)` Calculates the horizontal scroll amount necessary to make the given view fully visible inside the RecyclerView.
`Int`	`calculateDyToMakeVisible(view: View!, snapPreference: Int)` Calculates the vertical scroll amount necessary to make the given view fully visible inside the RecyclerView.

Protected functions
`Float`	`calculateSpeedPerPixel(displayMetrics: DisplayMetrics!)` Calculates the scroll speed.
`Int`	`calculateTimeForDeceleration(dx: Int)` Calculates the time for deceleration so that transition from LinearInterpolator to DecelerateInterpolator looks smooth.
`Int`	`calculateTimeForScrolling(dx: Int)` Calculates the time it should take to scroll the given distance (in pixels)
`Int`	`getHorizontalSnapPreference()` When scrolling towards a child view, this method defines whether we should align the left or the right edge of the child with the parent RecyclerView.
`Int`	`getVerticalSnapPreference()` When scrolling towards a child view, this method defines whether we should align the top or the bottom edge of the child with the parent RecyclerView.
`Unit`	`onSeekTargetStep( dx: Int, dy: Int, state: RecyclerView.State!, action: RecyclerView.SmoothScroller.Action! )` RecyclerView will call this method each time it scrolls until it can find the target position in the layout.
`Unit`	`onStart()` Called when smooth scroll is started.
`Unit`	`onStop()` Called when smooth scroller is stopped.
`Unit`	`onTargetFound( targetView: View!, state: RecyclerView.State!, action: RecyclerView.SmoothScroller.Action! )` Called when the target position is laid out.
`Unit`	`updateActionForInterimTarget( action: RecyclerView.SmoothScroller.Action! )` When the target scroll position is not a child of the RecyclerView, this method calculates a direction vector towards that child and triggers a smooth scroll.

Protected properties
`DecelerateInterpolator!`	`mDecelerateInterpolator`
`Int`	`mInterimTargetDx`
`Int`	`mInterimTargetDy`
`LinearInterpolator!`	`mLinearInterpolator`
`PointF!`	`mTargetVector`

Inherited functions

From androidx.recyclerview.widget.RecyclerView.SmoothScroller

`PointF?`	`computeScrollVectorForPosition(targetPosition: Int)` Compute the scroll vector for a given target position.
`View!`	`findViewByPosition(position: Int)`
`Int`	`getChildCount()`
`Int`	`getChildPosition(view: View!)`
`RecyclerView.LayoutManager?`	`getLayoutManager()`
`Int`	`getTargetPosition()` Returns the adapter position of the target item
`Unit`	`instantScrollToPosition(position: Int)` This function is deprecated. Use `jumpTo`.
`Boolean`	`isPendingInitialRun()` Returns true if SmoothScroller has been started but has not received the first animation callback yet.
`Boolean`	`isRunning()`
`Unit`	`normalize(scrollVector: PointF)` Normalizes the vector.
`Unit`	`onChildAttachedToWindow(child: View!)`
`Unit`	`setTargetPosition(targetPosition: Int)`
`Unit`	`stop()` Stops running the SmoothScroller in each animation callback.

Constants

SNAP_TO_ANY

Added in 1.0.0

const val SNAP_TO_ANY = 0: Int

Decides if the child should be snapped from start or end, depending on where it currently is in relation to its parent.

For instance, if the view is virtually on the left of RecyclerView, using SNAP_TO_ANY is the same as using SNAP_TO_START

See also
`calculateDtToFit`
`calculateDxToMakeVisible`
`calculateDyToMakeVisible`

SNAP_TO_END

Added in 1.0.0

const val SNAP_TO_END = 1: Int

Align child view's right or bottom with parent view's right or bottom

See also
`calculateDtToFit`
`calculateDxToMakeVisible`
`calculateDyToMakeVisible`

SNAP_TO_START

Added in 1.0.0

const val SNAP_TO_START = -1: Int

Align child view's left or top with parent view's left or top

See also
`calculateDtToFit`
`calculateDxToMakeVisible`
`calculateDyToMakeVisible`

Public constructors

LinearSmoothScroller

Added in 1.0.0

LinearSmoothScroller(context: Context!)

Public functions

calculateDtToFit

Added in 1.0.0

fun calculateDtToFit(
    viewStart: Int,
    viewEnd: Int,
    boxStart: Int,
    boxEnd: Int,
    snapPreference: Int
): Int

Helper method for calculateDxToMakeVisible and calculateDyToMakeVisible

calculateDxToMakeVisible

Added in 1.0.0

fun calculateDxToMakeVisible(view: View!, snapPreference: Int): Int

Calculates the horizontal scroll amount necessary to make the given view fully visible inside the RecyclerView.

Parameters
`view: View!`	The view which we want to make fully visible
`snapPreference: Int`	The edge which the view should snap to when entering the visible area. One of `SNAP_TO_START`, `SNAP_TO_END` or `SNAP_TO_END`

Returns
`Int`	The vertical scroll amount necessary to make the view visible with the given snap preference.

calculateDyToMakeVisible

Added in 1.0.0

fun calculateDyToMakeVisible(view: View!, snapPreference: Int): Int

Calculates the vertical scroll amount necessary to make the given view fully visible inside the RecyclerView.

Parameters
`view: View!`	The view which we want to make fully visible
`snapPreference: Int`	The edge which the view should snap to when entering the visible area. One of `SNAP_TO_START`, `SNAP_TO_END` or `SNAP_TO_ANY`.

Returns
`Int`	The vertical scroll amount necessary to make the view visible with the given snap preference.

Protected functions

calculateSpeedPerPixel

Added in 1.0.0

protected fun calculateSpeedPerPixel(displayMetrics: DisplayMetrics!): Float

Calculates the scroll speed.

By default, LinearSmoothScroller assumes this method always returns the same value and caches the result of calling it.

Parameters
`displayMetrics: DisplayMetrics!`	DisplayMetrics to be used for real dimension calculations

Returns
`Float`	The time (in ms) it should take for each pixel. For instance, if returned value is 2 ms, it means scrolling 1000 pixels with LinearInterpolation should take 2 seconds.

calculateTimeForDeceleration

Added in 1.0.0

protected fun calculateTimeForDeceleration(dx: Int): Int

Calculates the time for deceleration so that transition from LinearInterpolator to DecelerateInterpolator looks smooth.

Parameters
`dx: Int`	Distance to scroll

Returns
`Int`	Time for DecelerateInterpolator to smoothly traverse the distance when transitioning from LinearInterpolation

calculateTimeForScrolling

Added in 1.0.0

protected fun calculateTimeForScrolling(dx: Int): Int

Calculates the time it should take to scroll the given distance (in pixels)

Parameters
`dx: Int`	Distance in pixels that we want to scroll

Returns
`Int`	Time in milliseconds

See also
`calculateSpeedPerPixel`

getHorizontalSnapPreference

Added in 1.0.0

protected fun getHorizontalSnapPreference(): Int

When scrolling towards a child view, this method defines whether we should align the left or the right edge of the child with the parent RecyclerView.

Returns
`Int`	SNAP_TO_START, SNAP_TO_END or SNAP_TO_ANY; depending on the current target vector

See also
`SNAP_TO_START`
`SNAP_TO_END`
`SNAP_TO_ANY`

getVerticalSnapPreference

Added in 1.0.0

protected fun getVerticalSnapPreference(): Int

When scrolling towards a child view, this method defines whether we should align the top or the bottom edge of the child with the parent RecyclerView.

Returns
`Int`	SNAP_TO_START, SNAP_TO_END or SNAP_TO_ANY; depending on the current target vector

See also
`SNAP_TO_START`
`SNAP_TO_END`
`SNAP_TO_ANY`

Added in 1.4.0

protected fun onSeekTargetStep(
    dx: Int,
    dy: Int,
    state: RecyclerView.State!,
    action: RecyclerView.SmoothScroller.Action!
): Unit

RecyclerView will call this method each time it scrolls until it can find the target position in the layout.

SmoothScroller should check dx, dy and if scroll should be changed, update the provided to define the next scroll.

onStart

Added in 1.4.0

protected fun onStart(): Unit

Called when smooth scroll is started. This might be a good time to do setup.

onStop

Added in 1.4.0

protected fun onStop(): Unit

Called when smooth scroller is stopped. This is a good place to cleanup your state etc.

Added in 1.4.0

protected fun onTargetFound(
    targetView: View!,
    state: RecyclerView.State!,
    action: RecyclerView.SmoothScroller.Action!
): Unit

Called when the target position is laid out. This is the last callback SmoothScroller will receive and it should update the provided to define the scroll details towards the target view.

Added in 1.0.0

protected fun updateActionForInterimTarget(
    action: RecyclerView.SmoothScroller.Action!
): Unit

When the target scroll position is not a child of the RecyclerView, this method calculates a direction vector towards that child and triggers a smooth scroll.

See also
`computeScrollVectorForPosition`

Protected properties

mDecelerateInterpolator

Added in 1.0.0

protected val mDecelerateInterpolator: DecelerateInterpolator!

mInterimTargetDx

Added in 1.0.0

protected val mInterimTargetDx: Int

mInterimTargetDy

Added in 1.0.0

protected val mInterimTargetDy: Int

mLinearInterpolator

Added in 1.0.0

protected val mLinearInterpolator: LinearInterpolator!

mTargetVector

Added in 1.0.0

protected val mTargetVector: PointF!