public final class VelocityTracker extends Object
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(MotionEvent)
. When you want to determine the velocity call
computeCurrentVelocity(int)
and then call getXVelocity(int)
and getYVelocity(int)
to retrieve the velocity for each pointer id.Modifier and Type | Class and Description |
---|---|
static class |
VelocityTracker.Estimator
An estimator for the movements of a pointer based on a polynomial model.
|
Modifier and Type | Method and Description |
---|---|
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.
|
protected void |
finalize()
Called by the garbage collector on an object when garbage collection
determines that there are no more references to the object.
|
boolean |
getEstimator(int id,
VelocityTracker.Estimator outEstimator)
Get an estimator for the movements of a pointer using past movements of the
pointer to predict future movements.
|
float |
getXVelocity()
Retrieve the last computed X velocity.
|
float |
getXVelocity(int id)
Retrieve the last computed X velocity.
|
float |
getYVelocity()
Retrieve the last computed Y velocity.
|
float |
getYVelocity(int id)
Retrieve the last computed Y velocity.
|
static VelocityTracker |
obtain()
Retrieve a new VelocityTracker object to watch the velocity of a
motion.
|
static VelocityTracker |
obtain(String strategy)
Obtains a velocity tracker with the specified strategy.
|
void |
recycle()
Return a VelocityTracker object back to be re-used by others.
|
public static VelocityTracker obtain()
recycle()
when done. You should
generally only maintain an active object while tracking a movement,
so that the VelocityTracker can be re-used elsewhere.public static VelocityTracker obtain(String strategy)
strategy
- The strategy, or null to use the default.public void recycle()
protected void finalize() throws Throwable
Object
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 JavaTM 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.
public void clear()
public void addMovement(MotionEvent event)
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.event
- The MotionEvent you received and would like to track.public void computeCurrentVelocity(int units)
computeCurrentVelocity(int, float)
with a maximum
velocity of Float.MAX_VALUE.computeCurrentVelocity(int, float)
public void computeCurrentVelocity(int units, float maxVelocity)
getXVelocity()
and
getYVelocity()
.units
- The units you would like the velocity in. A value of 1
provides pixels per millisecond, 1000 provides pixels per second, etc.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.public float getXVelocity()
computeCurrentVelocity(int)
before calling this function.public float getYVelocity()
computeCurrentVelocity(int)
before calling this function.public float getXVelocity(int id)
computeCurrentVelocity(int)
before calling this function.id
- Which pointer's velocity to return.public float getYVelocity(int id)
computeCurrentVelocity(int)
before calling this function.id
- Which pointer's velocity to return.public boolean getEstimator(int id, VelocityTracker.Estimator outEstimator)
computeCurrentVelocity(int)
before calling
this method.id
- Which pointer's velocity to return.outEstimator
- The estimator to populate.