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 |
addMovement(event: MotionEvent!) Add a user's movement to the tracker. |
Unit |
clear() Reset the velocity tracker back to its initial state. |
Unit |
computeCurrentVelocity(units: Int) Equivalent to invoking |
Unit |
computeCurrentVelocity(units: Int, maxVelocity: Float) Compute the current velocity based on the points that have been collected. |
Float |
getAxisVelocity(axis: Int, id: Int) Retrieve the last computed velocity for a given motion axis. |
Float |
getAxisVelocity(axis: Int) Equivalent to calling |
Float |
Retrieve the last computed X velocity. |
Float |
getXVelocity(id: Int) Retrieve the last computed X velocity. |
Float |
Retrieve the last computed Y velocity. |
Float |
getYVelocity(id: Int) Retrieve the last computed Y velocity. |
Boolean |
isAxisSupported(axis: Int) Checks whether a given velocity-trackable |
static VelocityTracker! |
obtain() Retrieve a new VelocityTracker object to watch the velocity of a motion. |
Unit |
recycle() Return a VelocityTracker object back to be re-used by others. |
Protected methods | |
---|---|
Unit |
finalize() |
Public methods
addMovement
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. |
computeCurrentVelocity
fun computeCurrentVelocity(units: Int): Unit
Equivalent to invoking computeCurrentVelocity(int,float)
with a maximum velocity of Float.MAX_VALUE.
See Also
computeCurrentVelocity
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
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:
-
MotionEvent#AXIS_SCROLL
: supported startingandroid.os.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 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. |
See Also
getAxisVelocity
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. |
getXVelocity
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
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
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
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
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
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
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
protected fun finalize(): Unit
Exceptions | |
---|---|
java.lang.Throwable |
the Exception raised by this method |