HI Werner,
Thanks. <x:saveState> does not work in this case. Data saved using <saveState> are only available to the immediately following request.(post back in most cases).
When user click Back, the browser says something like "not available since previous Form post, ask to refresh ". When use click Refresh, the data saved using <x:saveState> is not there any more because it is not immediate POST back.
Dave
Werner Punz <[EMAIL PROTECTED]> wrote:
Werner Punz <[EMAIL PROTECTED]> wrote:
Dave wrote:
> When a backing bean is dependent on some data that are initialized
> by previous page, it works fine normally. But if user click Back/Refresh
> on browser, then the data is not available anymore to the backing bean.
> This will result in NullPointerException because the data is null. How
> to catch this issue and display a nice informative message, definitely
> not Exception? Thanks for ideas. Dave
>
Sorry, my first answer was too short, to clarify things a little bit,
the problem you encounter is due to the request scope, a bean declared
in request scope lives only one request, now if you do a refresh you might lose
important data along the way, the same goes for back.
There are various solutions to the problem, the shale token stuff, I yet have to check out,
but one solution is to use constructs w hich enable scopes bigger than request.
One solution definitely would be to dump the backend bean into the session
that way non traversed values would survive a refresh.
Another one would be to use a lot of hidden fields, for the non visible data which has to survive
which is a maintenance nightmare.
Generally the currently possibly best approach would be to use x:saveState which stores
beans for every page where a x:saveState tag is hit with the same declaration,
or to use some kinde of dialog-scoping system:
Following systems currently are available:
Shale Dialog
Seam
Seam at least is rather heavy on the configuration side, but it looks like the most interesting
approach in this area.
Shale Dialog I have not looked into yet,
the possible most lightweight approach however probably is x:saveState...
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