Added in API level 1

Summary: Methods | Protected Methods | Inherited Methods

VelocityTracker

Kotlin |Java

public final class VelocityTracker
extends Object

java.lang.Object
↳	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
`void`	`addMovement(MotionEvent event)` Add a user's movement to the tracker.
`void`	`clear()` Reset the velocity tracker back to its initial state.
`void`	`computeCurrentVelocity(int units)` Equivalent to invoking `computeCurrentVelocity(int, float)` with a maximum velocity of Float.MAX_VALUE.
`void`	`computeCurrentVelocity(int units, float maxVelocity)` Compute the current velocity based on the points that have been collected.
`float`	`getAxisVelocity(int axis, int id)` Retrieve the last computed velocity for a given motion axis.
`float`	`getAxisVelocity(int axis)` Equivalent to calling `getAxisVelocity(int, int)` for `axis` and the active pointer.
`float`	`getXVelocity(int id)` Retrieve the last computed X velocity.
`float`	`getXVelocity()` Retrieve the last computed X velocity.
`float`	`getYVelocity()` Retrieve the last computed Y velocity.
`float`	`getYVelocity(int id)` Retrieve the last computed Y velocity.
`boolean`	`isAxisSupported(int axis)` 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`	`obtain()` Retrieve a new VelocityTracker object to watch the velocity of a motion.
`void`	`recycle()` Return a VelocityTracker object back to be re-used by others.

Protected methods
`void`	`finalize()` Called by the garbage collector on an object when garbage collection determines that there are no more references to the object.

Inherited methods

From class


        
          java.lang.Object

`Object`	`clone()` Creates and returns a copy of this object.
`boolean`	`equals(Object obj)` Indicates whether some other object is "equal to" this one.
`void`	`finalize()` Called by the garbage collector on an object when garbage collection determines that there are no more references to the object.
`final Class<?>`	`getClass()` Returns the runtime class of this `Object`.
`int`	`hashCode()` Returns a hash code value for the object.
`final void`	`notify()` Wakes up a single thread that is waiting on this object's monitor.
`final void`	`notifyAll()` Wakes up all threads that are waiting on this object's monitor.
`String`	`toString()` Returns a string representation of the object.
`final void`	`wait(long timeoutMillis, int nanos)` Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.
`final void`	`wait(long timeoutMillis)` Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.
`final void`	`wait()` Causes the current thread to wait until it is awakened, typically by being notified or interrupted.

Public methods

addMovement

Added in API level 1

public void addMovement (MotionEvent event)

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

public void clear ()

Reset the velocity tracker back to its initial state.

computeCurrentVelocity

Added in API level 1

public void computeCurrentVelocity (int units)

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

Parameters
`units`	`int`

See also:

computeCurrentVelocity(int, float)

computeCurrentVelocity

Added in API level 4

public void computeCurrentVelocity (int units, 
                float maxVelocity)

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

public float getAxisVelocity (int axis, 
                int id)

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:

MotionEvent#AXIS_SCROLL: supported starting Build.VERSION_CODES.UPSIDE_DOWN_CAKE

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 `MotionEvent.AXIS_X`, `MotionEvent.AXIS_Y`, or `MotionEvent.AXIS_SCROLL`
`id`	`int`: Which pointer's velocity to return.

Returns
`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.

See also:

isAxisSupported(int)

getAxisVelocity

Added in API level 34

public float getAxisVelocity (int axis)

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

Parameters
`axis`	`int`: Which axis' velocity to return. Value is `MotionEvent.AXIS_X`, `MotionEvent.AXIS_Y`, or `MotionEvent.AXIS_SCROLL`

Returns
`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.

See also:

getXVelocity

Added in API level 8

public float getXVelocity (int id)

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.

Returns
`float`	The previously computed X velocity.

getXVelocity

Added in API level 1

public float getXVelocity ()

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

Returns
`float`	The previously computed X velocity.

getYVelocity

Added in API level 1

public float getYVelocity ()

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

Returns
`float`	The previously computed Y velocity.

getYVelocity

Added in API level 8

public float getYVelocity (int id)

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.

Returns
`float`	The previously computed Y velocity.

isAxisSupported

Added in API level 34

public boolean isAxisSupported (int axis)

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 `MotionEvent.AXIS_X`, `MotionEvent.AXIS_Y`, or `MotionEvent.AXIS_SCROLL`

Returns
`boolean`	`true` if `axis` is supported for velocity tracking, or `false` otherwise.

See also:

obtain

Added in API level 1

public static VelocityTracker obtain ()

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.

Returns
`VelocityTracker`	Returns a new VelocityTracker.

recycle

Added in API level 1

public void recycle ()

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 void finalize ()

Called by the garbage collector on an object when garbage collection determines that there are no more references to the object. A subclass overrides the finalize method to dispose of system resources or to perform other cleanup.

The general contract of finalize is that it is invoked if and when the Java virtual machine has determined that there is no longer any means by which this object can be accessed by any thread that has not yet died, except as a result of an action taken by the finalization of some other object or class which is ready to be finalized. The finalize method may take any action, including making this object available again to other threads; the usual purpose of finalize, however, is to perform cleanup actions before the object is irrevocably discarded. For example, the finalize method for an object that represents an input/output connection might perform explicit I/O transactions to break the connection before the object is permanently discarded.

The finalize method of class Object performs no special action; it simply returns normally. Subclasses of Object may override this definition.

The Java programming language does not guarantee which thread will invoke the finalize method for any given object. It is guaranteed, however, that the thread that invokes finalize will not be holding any user-visible synchronization locks when finalize is invoked. If an uncaught exception is thrown by the finalize method, the exception is ignored and finalization of that object terminates.

After the finalize method has been invoked for an object, no further action is taken until the Java virtual machine has again determined that there is no longer any means by which this object can be accessed by any thread that has not yet died, including possible actions by other objects or classes which are ready to be finalized, at which point the object may be discarded.

The finalize method is never invoked more than once by a Java virtual machine for any given object.

Any exception thrown by the finalize method causes the finalization of this object to be halted, but is otherwise ignored.

Throws
`Throwable`