Support Async Loading of Items

[roomtek]

I am using setDataProvider().

but in my AbstractBackEndDataProvider, sizeInBackEnd() is never called, and so all items are loaded from the backend instead of "as needed" as defined in the javadoc

[heruan]

I see this more a bug than an enhancement: it hangs the UI if the data source has many (e.g. thousands) of items, since it fetches all of them at once.

Calls to data provider should be filtered and limited, as in Vaadin's ComboBox.

[gatanaso]

Thank you for the feedback.

The reason why I have seen this as an enhancement is that providing this feature requires a bit more work in order to properly handle "lazy loading" as it's done in the Vaadin ComboBox. I agree that loading thousands of items will definitely block the UI and that does not provide a good user experience.

When I have more time I will try to investigate this further and see if it's possible to add this functionality.