public final class VelocityTracker extends Object implements Poolable<VelocityTracker>
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()
Invoked when the garbage collector has detected that this instance is no longer reachable.
|
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.
|
VelocityTracker |
getNextPoolable() |
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.
|
boolean |
isPooled() |
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.
|
void |
setNextPoolable(VelocityTracker element) |
void |
setPooled(boolean isPooled) |
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()
public void setNextPoolable(VelocityTracker element)
setNextPoolable
in interface Poolable<VelocityTracker>
public VelocityTracker getNextPoolable()
getNextPoolable
in interface Poolable<VelocityTracker>
public boolean isPooled()
isPooled
in interface Poolable<VelocityTracker>
public void setPooled(boolean isPooled)
setPooled
in interface Poolable<VelocityTracker>
protected void finalize() throws Throwable
Object
Note that objects that override finalize
are significantly more expensive than
objects that don't. Finalizers may be run a long time after the object is no longer
reachable, depending on memory pressure, so it's a bad idea to rely on them for cleanup.
Note also that finalizers are run on a single VM-wide finalizer thread,
so doing blocking work in a finalizer is a bad idea. A finalizer is usually only necessary
for a class that has a native peer and needs to call a native method to destroy that peer.
Even then, it's better to provide an explicit close
method (and implement
Closeable
), and insist that callers manually dispose of instances. This
works well for something like files, but less well for something like a BigInteger
where typical calling code would have to deal with lots of temporaries. Unfortunately,
code that creates lots of temporaries is the worst kind of code from the point of view of
the single finalizer thread.
If you must use finalizers, consider at least providing your own
ReferenceQueue
and having your own thread process that queue.
Unlike constructors, finalizers are not automatically chained. You are responsible for
calling super.finalize()
yourself.
Uncaught exceptions thrown by finalizers are ignored and do not terminate the finalizer thread. See Effective Java Item 7, "Avoid finalizers" for more.
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.