VelocityTrackerCompat

Added in 1.1.0

Kotlin |Java

public final class VelocityTrackerCompat

Helper for accessing features in VelocityTracker.

Summary

Public methods
`static void`	`addMovement(@NonNull VelocityTracker tracker, @NonNull MotionEvent event)` Add a user's movement to the tracker.
`static void`	`clear(@NonNull VelocityTracker tracker)` Reset the velocity tracker back to its initial state.
`static void`	`computeCurrentVelocity(@NonNull VelocityTracker tracker, int units)` Equivalent to invoking `computeCurrentVelocity` with a maximum velocity of Float.MAX_VALUE.
`static void`	`computeCurrentVelocity( @NonNull VelocityTracker tracker, int units, float maxVelocity )` Compute the current velocity based on the points that have been collected.
`static float`	`getAxisVelocity(@NonNull VelocityTracker tracker, int axis)` Equivalent to calling `getAxisVelocity` for `axis` and the active pointer.
`static float`	`getAxisVelocity(@NonNull VelocityTracker tracker, int axis, int pointerId)` Retrieve the last computed velocity for a given motion axis.
`static float`	`@ReplaceWith(expression = "tracker.getXVelocity(pointerId)") getXVelocity(VelocityTracker tracker, int pointerId)` This method is deprecated. Use `getXVelocity` directly.
`static float`	`@ReplaceWith(expression = "tracker.getYVelocity(pointerId)") getYVelocity(VelocityTracker tracker, int pointerId)` This method is deprecated. Use `getYVelocity` directly.
`static boolean`	`isAxisSupported(@NonNull VelocityTracker tracker, int axis)` Checks whether a given velocity-trackable `MotionEvent` axis is supported for velocity tracking by this `VelocityTracker` instance (refer to `getAxisVelocity` for a list of potentially velocity-trackable axes).
`static void`	`recycle(@NonNull VelocityTracker tracker)` Return a `VelocityTracker` object back to be re-used by others.

Public methods

addMovement

Added in 1.13.0

public static void addMovement(@NonNull VelocityTracker tracker, @NonNull MotionEvent event)

Add a user's movement to the tracker.

For pointer events, you should call this for the initial ACTION_DOWN, the following ACTION_MOVE events that you receive, and the final ACTION_UP. You can, however, call this for whichever events you desire.

Parameters
`@NonNull VelocityTracker tracker`	The `VelocityTracker` to add the movement to.
`@NonNull MotionEvent event`	The MotionEvent you received and would like to track.

clear

Added in 1.13.0

public static void clear(@NonNull VelocityTracker tracker)

Reset the velocity tracker back to its initial state.

computeCurrentVelocity

Added in 1.13.0

public static void computeCurrentVelocity(@NonNull VelocityTracker tracker, int units)

Equivalent to invoking computeCurrentVelocity with a maximum velocity of Float.MAX_VALUE.

computeCurrentVelocity

Added in 1.13.0

public static void computeCurrentVelocity(
    @NonNull VelocityTracker tracker,
    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 getAxisVelocity ()}.

Parameters
`@NonNull VelocityTracker tracker`	The `VelocityTracker` for which to compute velocity.
`int units`	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.
`float maxVelocity`	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 1.12.0

public static float getAxisVelocity(@NonNull VelocityTracker tracker, int axis)

Equivalent to calling getAxisVelocity for axis and the active pointer.

Parameters
`@NonNull VelocityTracker tracker`	The `VelocityTracker` from which to get axis velocity.
`int axis`	Which axis' velocity to return.

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
`isAxisSupported`
`getAxisVelocity`

getAxisVelocity

Added in 1.12.0

public static float getAxisVelocity(@NonNull VelocityTracker tracker, int axis, int pointerId)

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

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

AXIS_SCROLL: supported via the platform starting UPSIDE_DOWN_CAKE. Supported via a fallback logic at all platform levels for the active pointer only.

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

Parameters
`@NonNull VelocityTracker tracker`	The `VelocityTracker` from which to get axis velocity.
`int axis`	Which axis' velocity to return.
`int pointerId`	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`

getXVelocity

Added in 1.1.0

Deprecated in 1.1.0

@ReplaceWith(expression = "tracker.getXVelocity(pointerId)")
public static float getXVelocity(VelocityTracker tracker, int pointerId)

Call getXVelocity. If running on a pre-HONEYCOMB device, returns getXVelocity.

getYVelocity

Added in 1.1.0

Deprecated in 1.1.0

@ReplaceWith(expression = "tracker.getYVelocity(pointerId)")
public static float getYVelocity(VelocityTracker tracker, int pointerId)

Call getYVelocity. If running on a pre-HONEYCOMB device, returns getYVelocity.

isAxisSupported

Added in 1.12.0

public static boolean isAxisSupported(@NonNull VelocityTracker tracker, int axis)

Checks whether a given velocity-trackable MotionEvent axis is supported for velocity tracking by this VelocityTracker instance (refer to getAxisVelocity 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
`@NonNull VelocityTracker tracker`	The `VelocityTracker` for which to check axis support.
`int axis`	The axis to check for velocity support.

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

See also
`getAxisVelocity`
`getAxisVelocity`

recycle

Added in 1.13.0

public static void recycle(@NonNull VelocityTracker tracker)

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

Call this method for your VelocityTracker when you have finished tracking velocity for the use-case you created this tracker for and decided that you no longer need it. This allows it to be returned back to the pool of trackers to be re-used by others.

You must not touch the object after calling this function. That is, don't call any methods on it, or pass it as an input to any of this class' compat APIs, as the instance is no longer valid for velocity tracking.

See also
`recycle`