public
final
class
VelocityTracker
extends Object
| java.lang.Object | |
| ↳ | android.view.VelocityTracker |
Helper for tracking the velocity of touch 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(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.
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 |
void
|
computeCurrentVelocity(int units, float maxVelocity)
Compute the current velocity based on the points that have been collected. |
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. |
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
| |
void addMovement (MotionEvent event)
Add a user's movement to the tracker. 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 | |
|---|---|
event |
MotionEvent:
The MotionEvent you received and would like to track.
|
void computeCurrentVelocity (int units)
Equivalent to invoking computeCurrentVelocity(int, float) with a maximum
velocity of Float.MAX_VALUE.
| Parameters | |
|---|---|
units |
int
|
See also:
Developers
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 pixels per millisecond, 1000 provides pixels per second, etc. |
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.
|
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. |
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. |
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. |
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. |
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. |
void recycle ()
Return a VelocityTracker object back to be re-used by others. You must not touch the object after calling this function.
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 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.
| Throws | |
|---|---|
Throwable |
|