| 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 | |||||||||||
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Add a user's movement to the tracker.
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Reset the velocity tracker back to its initial state.
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Equivalent to invoking
computeCurrentVelocity(int, float) with a maximum
velocity of Float.MAX_VALUE. | |||||||||||
Compute the current velocity based on the points that have been
collected.
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Retrieve the last computed X velocity.
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Retrieve the last computed X velocity.
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Retrieve the last computed Y velocity.
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Retrieve the last computed Y velocity.
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Retrieve a new VelocityTracker object to watch the velocity of a
motion.
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Return a VelocityTracker object back to be re-used by others.
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| Protected Methods | |||||||||||
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Invoked when the garbage collector has detected that this instance is no longer reachable.
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[Expand]
Inherited Methods | |||||||||||
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From class
java.lang.Object
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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.
| event | The MotionEvent you received and would like to track. |
|---|
Equivalent to invoking computeCurrentVelocity(int, float) with a maximum
velocity of Float.MAX_VALUE.
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().
| 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. |
Retrieve the last computed X velocity. You must first call
computeCurrentVelocity(int) before calling this function.
Retrieve the last computed X velocity. You must first call
computeCurrentVelocity(int) before calling this function.
| id | Which pointer's velocity to return. |
|---|
Retrieve the last computed Y velocity. You must first call
computeCurrentVelocity(int) before calling this function.
| id | Which pointer's velocity to return. |
|---|
Retrieve the last computed Y velocity. You must first call
computeCurrentVelocity(int) before calling this function.
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 a VelocityTracker object back to be re-used by others. You must not touch the object after calling this function.
Invoked when the garbage collector has detected that this instance is no longer reachable. The default implementation does nothing, but this method can be overridden to free resources.
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.
| Throwable |
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