Android APIs
public abstract class

LinearSmoothScroller

extends RecyclerView.SmoothScroller
java.lang.Object
   ↳ android.support.v7.widget.RecyclerView.SmoothScroller
     ↳ android.support.v7.widget.LinearSmoothScroller

Class Overview

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

Summary

Constants
int SNAP_TO_ANY

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

int SNAP_TO_END Align child view's right or bottom with parent view's right or bottom
int SNAP_TO_START Align child view's left or top with parent view's left or top
Fields
protected final DecelerateInterpolator mDecelerateInterpolator
protected int mInterimTargetDx
protected int mInterimTargetDy
protected final LinearInterpolator mLinearInterpolator
protected PointF mTargetVector
Public Constructors
LinearSmoothScroller(Context context)
Public Methods
int calculateDtToFit(int viewStart, int viewEnd, int boxStart, int boxEnd, int snapPreference)
Helper method for calculateDxToMakeVisible(android.view.View, int) and calculateDyToMakeVisible(android.view.View, int)
int calculateDxToMakeVisible(View view, int snapPreference)
Calculates the horizontal scroll amount necessary to make the given view fully visible inside the RecyclerView.
int calculateDyToMakeVisible(View view, int snapPreference)
Calculates the vertical scroll amount necessary to make the given view fully visible inside the RecyclerView.
abstract PointF computeScrollVectorForPosition(int targetPosition)
Protected Methods
float calculateSpeedPerPixel(DisplayMetrics displayMetrics)
Calculates the scroll speed.
int calculateTimeForDeceleration(int dx)

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

int calculateTimeForScrolling(int dx)
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.
void onSeekTargetStep(int dx, int dy, RecyclerView.State state, RecyclerView.SmoothScroller.Action action)

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

void onStart()
Called when smooth scroll is started.
void onStop()
Called when smooth scroller is stopped.
void onTargetFound(View targetView, RecyclerView.State state, RecyclerView.SmoothScroller.Action action)
Called when the target position is laid out.
void updateActionForInterimTarget(RecyclerView.SmoothScroller.Action 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.
[Expand]
Inherited Methods
From class android.support.v7.widget.RecyclerView.SmoothScroller
From class java.lang.Object

Constants

public static final int SNAP_TO_ANY

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
Constant Value: 0 (0x00000000)

public static final int SNAP_TO_END

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

See Also
Constant Value: 1 (0x00000001)

public static final int SNAP_TO_START

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

See Also
Constant Value: -1 (0xffffffff)

Fields

protected final DecelerateInterpolator mDecelerateInterpolator

protected int mInterimTargetDx

protected int mInterimTargetDy

protected final LinearInterpolator mLinearInterpolator

protected PointF mTargetVector

Public Constructors

public LinearSmoothScroller (Context context)

Public Methods

public int calculateDtToFit (int viewStart, int viewEnd, int boxStart, int boxEnd, int snapPreference)

Helper method for calculateDxToMakeVisible(android.view.View, int) and calculateDyToMakeVisible(android.view.View, int)

public int calculateDxToMakeVisible (View view, int snapPreference)

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

Parameters
view The view which we want to make fully visible
snapPreference 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
  • The vertical scroll amount necessary to make the view visible with the given snap preference.

public int calculateDyToMakeVisible (View view, int snapPreference)

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

Parameters
view The view which we want to make fully visible
snapPreference 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
  • The vertical scroll amount necessary to make the view visible with the given snap preference.

public abstract PointF computeScrollVectorForPosition (int targetPosition)

Protected Methods

protected float calculateSpeedPerPixel (DisplayMetrics displayMetrics)

Calculates the scroll speed.

Parameters
displayMetrics DisplayMetrics to be used for real dimension calculations
Returns
  • 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.

protected int calculateTimeForDeceleration (int dx)

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

Parameters
dx Distance to scroll
Returns
  • Time for DecelerateInterpolator to smoothly traverse the distance when transitioning from LinearInterpolation

protected int calculateTimeForScrolling (int dx)

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

Parameters
dx Distance in pixels that we want to scroll
Returns
  • Time in milliseconds
See Also

protected 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.

Returns
  • SNAP_TO_START, SNAP_TO_END or SNAP_TO_ANY; depending on the current target vector
See Also

protected 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.

Returns
  • SNAP_TO_START, SNAP_TO_END or SNAP_TO_ANY; depending on the current target vector
See Also

protected void onSeekTargetStep (int dx, int dy, RecyclerView.State state, RecyclerView.SmoothScroller.Action action)

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 RecyclerView.SmoothScroller.Action to define the next scroll.

Parameters
dx Last scroll amount horizontally
dy Last scroll amount verticaully
state Transient state of RecyclerView
action If you want to trigger a new smooth scroll and cancel the previous one, update this object.

protected void onStart ()

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

protected void onStop ()

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

protected void onTargetFound (View targetView, RecyclerView.State state, RecyclerView.SmoothScroller.Action action)

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

Parameters
targetView The view element which render the target position.
state Transient state of RecyclerView
action Action instance that you should update to define final scroll action towards the targetView

protected void updateActionForInterimTarget (RecyclerView.SmoothScroller.Action 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.

See Also