Vaadin Flow: Returning to a view, the view should not reload data from the backend - vaadin-flow

Question

Split out from Vaadin Dataprovider: how to avoid "auto-fetch"?.
Given a Vaadin Flow 19 app with a MainView extends AppLayout, a GridView and an EmptyView And #PreserveOnRefresh annotation is used on MainView.
When returning to GridView, the GridView should be exactly in the same state as before:
open GridView using button in MainView for the first time -> Grid uses DataProvider to fetch data from backend
enter "Spiderman" in TextField with caption "stateCheck"
switch to EmptyView using button in MainView
in the real app: do something in EmptyView and potentially other views
return to GridView using button in MainView for the 2nd time
Then (1) the TextField with caption "stateCheck" should display the value "Spiderman"
And (2) the grid should still show the same data as before; it should not reload the data from the backend
Observed behaviour:
(1) is ok, but (2) not: the grid always calls fetch method to get data from the backend.
How do I achieve the desired behavior?
Here's the code of my GridView which also fakes the backend DataProvider:
#Route(value = "grid", layout = MainView.class)
public class GridView extends VerticalLayout {
public GridView() {
final Grid<Person> g = new Grid(Person.class);
g.setColumns("name");
g.setDataProvider(DataProvider.fromCallbacks(q -> fetch(q), q -> count(q)));
add(g);
add(new TextField("State check"));
}
// fake DataProvider
private int count(Query<Person, Void> q) { return 3; }
private Stream<Person> fetch(Query<Person, Void> q) {
q.getLimit(); //vaadin checks these have been called
q.getOffset(); //vaadin checks these have been called
System.out.println("fetching again");
return Arrays.asList(new Person("1"), new Person("2"), new Person("3")).stream();
}
}
MainView is used to switch between GridView and EmptyView
#PreserveOnRefresh
public class MainView extends AppLayout {
private Component emptyBView;
private Component gridBView;
public MainView() {
final Button emptyB = new Button("Btn empty");
emptyB.addClickListener(e -> {
if (emptyBView == null) { emptyBView = new EmptyView();}
setContent(emptyBView);
});
addToNavbar(emptyB);
final Button gridB = new Button("Btn grid");
gridB.addClickListener(e -> {
if (gridBView == null) gridBView = new GridView();
setContent(gridBView);
});
addToNavbar(gridB);
}
}

Answer 1

This is actually intentional behavior. The server side dataprovider listener needs to be removed when component is detached and rewired on attaching. The reason is that otherwise there would be listeners accumulating and producing a memory leakage. If you think your users would be using refresh page often, you should consider adding a cache to your application to optimize performance.
Now one could entertain with the idea of having this kind of caching of previous loaded data behavior via API in Grid also in Vaadin framework, as it may or may not be desirable. It is application specific.
If the use case of refreshing is really to get the fresh data of live and active database, it is actually desired that data is loaded when page is refreshed.
If the desire is to avoid extra bombarding of DB as data is known to be static, you want to have caching.