Added in API level 1

VelocityTracker

class VelocityTracker
kotlin.Any
   ↳ android.view.VelocityTracker

Helper for tracking the velocity of motion events, for implementing flinging and other such gestures. Use obtain to retrieve a new instance of the class when you are going to begin tracking. Put the motion events you receive into it with addMovement(android.view.MotionEvent). When you want to determine the velocity, call computeCurrentVelocity(int) and then call the velocity-getter methods like getXVelocity(int), getYVelocity(int), or getAxisVelocity(int,int) to retrieve velocity for different axes and/or pointer IDs.

Summary

Public methods
Unit

Add a user's movement to the tracker.
Unit

Reset the velocity tracker back to its initial state.
Unit

Equivalent to invoking computeCurrentVelocity(int,float) with a maximum velocity of Float.
Unit
computeCurrentVelocity(units: Int, maxVelocity: Float)

Compute the current velocity based on the points that have been collected.
Float

Equivalent to calling getAxisVelocity(int,int) for axis and the active pointer.
Float
getAxisVelocity(axis: Int, id: Int)

Retrieve the last computed velocity for a given motion axis.
Float

Retrieve the last computed X velocity.
Float

Retrieve the last computed X velocity.
Float

Retrieve the last computed Y velocity.
Float

Retrieve the last computed Y velocity.
Boolean

Checks whether a given velocity-trackable MotionEvent axis is supported for velocity tracking by this VelocityTracker instance (refer to getAxisVelocity(int,int) for a list of potentially velocity-trackable axes).
static VelocityTracker!

Retrieve a new VelocityTracker object to watch the velocity of a motion.
Unit

Return a VelocityTracker object back to be re-used by others.
Protected methods
Unit

Public methods

addMovement

Added in API level 1
fun addMovement(event: MotionEvent!): Unit

Add a user's movement to the tracker. You should call this for the initial MotionEvent.ACTION_DOWN, the following MotionEvent.ACTION_MOVE events that you receive, and the final MotionEvent.ACTION_UP. You can, however, call this for whichever events you desire.

Parameters
event MotionEvent!: The MotionEvent you received and would like to track.

clear

Added in API level 1
fun clear(): Unit

Reset the velocity tracker back to its initial state.

computeCurrentVelocity

Added in API level 1
fun computeCurrentVelocity(units: Int): Unit

Equivalent to invoking computeCurrentVelocity(int,float) with a maximum velocity of Float.MAX_VALUE.

computeCurrentVelocity

Added in API level 4
fun computeCurrentVelocity(
    units: Int, 
    maxVelocity: Float
): Unit

Compute the current velocity based on the points that have been collected. Only call this when you actually want to retrieve velocity information, as it is relatively expensive. You can then retrieve the velocity with getXVelocity() and getYVelocity().

Parameters
units Int: The units you would like the velocity in. A value of 1 provides units per millisecond, 1000 provides units per second, etc. Note that the units referred to here are the same units with which motion is reported. For axes X and Y, the units are pixels.
maxVelocity Float: The maximum velocity that can be computed by this method. This value must be declared in the same unit as the units parameter. This value must be positive.

getAxisVelocity

Added in API level 34
fun getAxisVelocity(axis: Int): Float

Equivalent to calling getAxisVelocity(int,int) for axis and the active pointer.

Parameters
axis Int: Which axis' velocity to return. Value is android.view.MotionEvent#AXIS_X, android.view.MotionEvent#AXIS_Y, or android.view.MotionEvent#AXIS_SCROLL
Return
Float The previously computed velocity for axis for the active pointer if axis is supported for velocity tracking, or 0 if velocity tracking is not supported for the axis.

getAxisVelocity

Added in API level 34
fun getAxisVelocity(
    axis: Int, 
    id: Int
): Float

Retrieve the last computed velocity for a given motion axis. You must first call computeCurrentVelocity(int) or computeCurrentVelocity(int,float) before calling this function.

In addition to MotionEvent.AXIS_X and MotionEvent.AXIS_Y which have been supported since the introduction of this class, the following axes can be candidates for this method:

Before accessing velocities of an axis using this method, check that your VelocityTracker instance supports the axis by using isAxisSupported(int).

Parameters
axis Int: Which axis' velocity to return. Value is android.view.MotionEvent#AXIS_X, android.view.MotionEvent#AXIS_Y, or android.view.MotionEvent#AXIS_SCROLL
id Int: Which pointer's velocity to return.
Return
Float The previously computed velocity for axis for pointer ID of id if axis is supported for velocity tracking, or 0 if velocity tracking is not supported for the axis.

getXVelocity

Added in API level 1
fun getXVelocity(): Float

Retrieve the last computed X velocity. You must first call computeCurrentVelocity(int) before calling this function.

Return
Float The previously computed X velocity.

getXVelocity

Added in API level 8
fun getXVelocity(id: Int): Float

Retrieve the last computed X velocity. You must first call computeCurrentVelocity(int) before calling this function.

Parameters
id Int: Which pointer's velocity to return.
Return
Float The previously computed X velocity.

getYVelocity

Added in API level 1
fun getYVelocity(): Float

Retrieve the last computed Y velocity. You must first call computeCurrentVelocity(int) before calling this function.

Return
Float The previously computed Y velocity.

getYVelocity

Added in API level 8
fun getYVelocity(id: Int): Float

Retrieve the last computed Y velocity. You must first call computeCurrentVelocity(int) before calling this function.

Parameters
id Int: Which pointer's velocity to return.
Return
Float The previously computed Y velocity.

isAxisSupported

Added in API level 34
fun isAxisSupported(axis: Int): Boolean

Checks whether a given velocity-trackable MotionEvent axis is supported for velocity tracking by this VelocityTracker instance (refer to getAxisVelocity(int,int) for a list of potentially velocity-trackable axes).

Note that the value returned from this method will stay the same for a given instance, so a single check for axis support is enough per a VelocityTracker instance.

Parameters
axis Int: The axis to check for velocity support. Value is android.view.MotionEvent#AXIS_X, android.view.MotionEvent#AXIS_Y, or android.view.MotionEvent#AXIS_SCROLL
Return
Boolean true if axis is supported for velocity tracking, or false otherwise.

obtain

Added in API level 1
static fun obtain(): VelocityTracker!

Retrieve a new VelocityTracker object to watch the velocity of a motion. Be sure to call recycle when done. You should generally only maintain an active object while tracking a movement, so that the VelocityTracker can be re-used elsewhere.

Return
VelocityTracker! Returns a new VelocityTracker.

recycle

Added in API level 1
fun recycle(): Unit

Return a VelocityTracker object back to be re-used by others. You must not touch the object after calling this function.

Protected methods

finalize

Added in API level 1
protected fun finalize(): Unit
Exceptions
java.lang.Throwable the Exception raised by this method