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From Braden Shepherdson <bra...@chromium.org>
Subject Wiping plugins on navigation
Date Wed, 05 Sep 2012 20:15:11 GMT
This is intended as a continuation of the discussion started in
https://issues.apache.org/jira/browse/CB-1318 .

The bug in question is one where one page starts a long native side action
such as a network call. Then the user navigates the app to another page.
When the long action completes, the call returns and the appropriate
Javascript callback is looked up and called.

However when the page is navigated, the counter that provides supposedly
unique names for callbacks is reset, allowing a callback on the new page to
have the same name as the callback from the old page. It then gets called
incorrectly, potentially introducing weird and transient bugs.

The proposed solution is to do the following on navigation:
- Call a destroy() call on all plugins, which by default does nothing. This
allows the plugins a chance to cancel any outstanding network requests or
do any other cleanup work.
- Delete the plugin instance and recreate it.

In the bug I also said one step would be to wipe the callback table in the
Javascript, but that isn't necessary since it would have been wiped by the
navigation anyway.

This issue is cross-platform-ish. It (probably) doesn't apply to web-based
platforms like WebOS or Bada, because the plugins are Javascript shims
rather than native code, and are wiped on navigation like any other
Javascript. However this issue does exist on at least Android and iOS, and
probably a few others as well.

I'm proposing to implement the solution outlined above on Android and iOS.
I don't have the devices or environment to do any other platforms, nor am I
sure which are necessary. The maintainers of other platforms will have to
consider this problem for their platform. I would also update the core
plugins to define a destroy() method if they have relevant cleanups to make.

Thoughts on the approach, things I'm missing?

Braden

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