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From "Sean Nikolai Fridman (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CB-1462) False logic for native watchPosition/clearWatch
Date Mon, 17 Sep 2012 21:37:07 GMT

    [ https://issues.apache.org/jira/browse/CB-1462?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13457361#comment-13457361
] 

Sean Nikolai Fridman commented on CB-1462:
------------------------------------------

Alrighty, but that doesn't affect the issue I experienced with the native Android code. 

Android still won't know whether it can disable location update listeners on clearWatch because
it will still have a callback id in its callback list. Eventually the callback will be called,
and yeah, with this fix the success callback JS side won't be run, but GPS/NetworkLocation
will still be running since it wasn't stopped on clearWatch.

I guess native could always check to shut off GPS on the win/fail callbacks? Would be curious
to know how other native implementations do it. I still wonder: can native really handle the
situation properly without knowing the callback is associated with a watch operation?
                
> False logic for native watchPosition/clearWatch
> -----------------------------------------------
>
>                 Key: CB-1462
>                 URL: https://issues.apache.org/jira/browse/CB-1462
>             Project: Apache Cordova
>          Issue Type: Bug
>          Components: Android, CordovaJS
>    Affects Versions: 2.0.0
>            Reporter: Sean Nikolai Fridman
>            Assignee: Filip Maj
>              Labels: clearwatch, geolocation, watchposition
>             Fix For: 2.2.0
>
>
> *Note:* This is a bug in Android's native geolocation implementation. I can't speak to
what happens on other platforms. However, I get the feeling that the bug is symptomatic of
the JS implementation so it might very well exist on more platforms.
> *Description:* When watchPosition is called, it first calls getCurrentLocation (resulting
in a native call to getLocation), then makes a native call to addWatch. In Android, addWatch
callback ids and getLocation callback ids are stored in separate data structures. The bug
I'm seeing is, when I call clearWatch before the watch operation's implicit getCurrentLocation
callback is invoked, the watch operation is removed/stopped in native, but the corresponding
getCurrentLocation operation is not.  This is not compliant with the W3C spec, which states
that that no further callbacks for the watch operation should be invoked. Worse, this causes
a bug on Android where GPS is never shut off! clearWatch stops the location listener *iff*
{{callbacks.size + watches.size == 0}}, and so if the callback hadn't been invoked yet...
> _(Actually, skimming back through the code, I'm not seeing anywhere where the location
listener is stopped after a getCurrentPosition. Which may be another issue... not sure.)_
> *And the potential issue in Javascript is this:* if native has no knowledge of which
getCurrentLocation callbacks are part of a watch operation and which are just normal independent
ones, how can it possibly remove the callback id for the implicit getCurrentLocation operation
on clearWatch? And how can it possibly know if it can really stop listening for location updates?

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