Handling next and prev buttons of SimplePager ??

[Santosh kumar]

Hi,

I am using GWT 2.3 cellTable to display the data using SimplePager.

And i am following the example AsyncDataProvider as it is...

http://code.google.com/webtoolkit/doc/latest/DevGuideUiCellWidgets.html


AsyncDataProvider provider = new AsyncDataProvider() {
      @Override
      protected void onRangeChanged(HasData display) {

        // Here i am doing rpc call to get the data using cursors... and its working fine.

        updateRowData(start, data);
      }
};

But each time when i click next button i am getting next 20 values from the data store using cursor. And it is displaying the data fine. No issues with next button.

But when i click prev button, i am assuming that cellTable had stored the previously displayed data, and just want to display that existing data, and
handle this case without making RPC ?? but here when i click on prev button, progress bar is being displayed... what is that wrong here ??

(DOUBT: on click of prev button: what is the need of call to the server to get the duplicate data again ??)

is their any other way to handle this case ?? Please any suggestions ??


Thanks in advance

--
Santosh Kumar K

www.AccountingGuru.in

[Miroslav Genov]

If you are using GAE cursors, then I'm mostly sure that they are forward only cursors. So if you want to make your pager working, you had to keep all received cursors in a list, to move back. 

So

[page-1] - > cursor null 

hit next

[page-2] -> cursor 1 

hit previous

[page-1] -> cursor null 

[page-1] - > cursor null 

hit next

[page-2] -> cursor 1 

hit next

[page-3] -> cursor 2 

hit previous

[page-2] -> cursor 1 (so when cursor2 is returned, you know how to move to page - 4, but don't know how to move to page 2.

[Santosh kumar]

Hi All,,

Because of some reason, Discussion subject changed to "Отг: Handling next and prev buttons of SimplePager ??" for a reply.
And here in gmail i got that reply as a new thread. So only i am replying from that new thread...

But my thread was:

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[Santosh kumar]

Hi Miroslav,

I have two questions:

1. If i am keeping track of cursors, and what if i click last page arrow button, then how do i get the last 20(assume) values ??
2. if i click prev arrow button then how do i display the last page(here i am understanding that pager holds the previous data so no need of call to the server).

[Miroslav Genov]

If i am keeping track of cursors, and what if i click last page arrow button, then how do i get the last 20(assume) values ??

• If we are talking in GAE context, in order to do that, you have to have a reference to the last cursor. I don't think that there is a way on GAE to retrieve the last cursor, so you can create a work-around over this by using a background task which iterates over list of entities and store the first and the last cursor values when new entity is added or existing is updated. I don't think that this is a good idea, because if you have a millions of rows then you have to use tons of CPU time to end this job, and the data that user sees will be in inconsistent state.

Why the people that are using your app are going to use that functionality ? I think that simple text search could help them to lookup for the thing that they are looking or maybe some kind of filter to filter data rows. 

• If are talking about SQL database, then I'm not sure why you ever have to use cursors at all. 

if i click prev arrow button then how do i display the last page(here i am understanding that pager holds the previous data so no need of call to the server).

• You can keep a reference to the last cursor position. 

To be honest, I'm not sure that GWT page functionality is made for GAE or any other datastore that is using cursors. Just pagination and cursors don't fit well together. 

[Santu]

My direct question is, when i click on the prev arrow button previous page is not displayed, instead progress bar is being
displayed ?? (here i am assume that pager holds the previous data so no need of call to the server, and itself displays the data).

is my assumption is correct ?? or is their any other way ??