Re: Strategy for saving data project

On Monday, July 2, 2012 9:31:56 AM UTC+2, Thomas Lefort wrote:

Hi,

I was relying on mayStop to save my user's project when they leave the activity but it seems to work in some cases only, ie when navigating from one activity to another but not when leaving the application or closing the browser... I don't know if it is normal? may be there is "not enough time" to send the last message with all the project's data?

That's basically what happens yes.

See http://code.google.com/p/google-web-toolkit/issues/detail?id=4898 and http://www.whatwg.org/specs/web-apps/current-work/multipage/history.html#navigating-across-documents among others.

 

If it is then I need a whole new strategy to make sure data is saved when the user leaves. I would be interested in knowing of any suggestion to solve the issue.

I have planned to save on every change made, but it is quite heavy as there are many frequent updates possible (just moving the map would trigger a save). An optimisation to this would be a combination of a flag for tracking changes and a timer to make periodic saves, eg every minute or so, when the project has changed.

Anyway if anyone has recommendations on how to do this I would be very happy hearing them.

See http://code.google.com/p/google-web-toolkit/issues/detail?id=6726#c5 

Basically: onbeforeunload (which calls mayStop of the activities) exists so that you can tell the user there are unsaved changes and he can cancel the navigation to save them before navigating away again.

With a PlaceChangeRequestEvent you could easily tell an onbeforeunload from an internal navigation (the target place is 'null'), but that isn't exposed to activities (mayStop). I suppose you could workaround this using a PlaceChangeRequestEvent.Handler (or Window.ClosingHandler) and shared state (considering mayStop methods are called first, they would store a flag in the shared state, and the PlaceChangeRequestEvent.Handler would setWarning if the target –place is 'null' –resp. the Window.ClosingHandler would setMessage– when the shared state indicates unsaved changes; but of course, you should also handle the case where the mayStop methods are called *last*); and you'd save data in your activities' onStop(), which are not called onbeforeunload.

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