I think I've got this figured out. Almost. With multi-touch support,
getAction() can return a compound value representing the pointerID in
the second byte and the action value in the first byte. For example,
if two fingers are down, and pointerID 1 is lifted (i.e., finger 2),
getAction() returns a value of 262 (0x100 or 256 to represent
pointerID 1, and 6 to represent up for a compound value of 0x106 or
262). I'm curious why it was done this way instead of using 0 for down
and 1 for up, even when pointers are involved. Things get a little
weird because of the differences. Here's an example (note I'm using a
Motorola Droid phone here so this may behave differently on other
devices):
Press finger 1 to the screen (action value of 0)
finger 1 gets pointerID 0, no problem, pointerID is 0, down is 0
Press finger 2 to the screen (action value of 261)
finger 2 gets pointerID 1, a little weird, could have been 256
instead?
Lift finger 1 from the screen (action value of 6)
finger 2 is still pointerID 1, action could still have been 1?
Lift finger 2 from the screen (action value of 1)
finger 2 is still pointerID 1, but the action value is not 262 or
257 it's 1
It would seem I can't use the bitmasks reliably in all cases. If I
always inspect the action value for the pointerID and the action
value, I get messed up at the end because pointerID has vanished. And
0 seems to be equivalent to 5, and 1 to 6.
Is this something you'd consider a bug or is this how it's supposed to
work? Should we expect it to continue to work this way?
Thanks for your help.
- dave
On Oct 27, 4:28 pm, Dianne Hackborn <[email protected]> wrote:
> On Tue, Oct 27, 2009 at 2:02 PM, MrChaz <[email protected]> wrote:
>
> > Thanks for the info,
>
> > Wouldn't this
> > Finger 1 up: MotionEvent ACTION_POINTER_1_UP with one pointer, whose
> > ID is
> > 1.
> > need to be ID of 0? Or am I mis-understanding the purpose of the UP
> > action?
>
> Good point. Actually my example was not very good because at the places
> where there is an up transition, the last position of the pointer going up
> is included in the event stream -- so in all of these, you would receive
> both 0 and 1. It is in the following move event that you will only get the
> information for the pointers that are currently down.
>
> --
> Dianne Hackborn
> Android framework engineer
> [email protected]
>
> Note: please don't send private questions to me, as I don't have time to
> provide private support, and so won't reply to such e-mails. All such
> questions should be posted on public forums, where I and others can see and
> answer them.
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