Set items to ListDataView directly (#4973)

* Set items to ListDataView directly

* Update explanation for filtering and selection handling

Clarify the reason for using ListDataView.setItems() over Grid.setItems() to preserve selection.

Author: peholmst

articles/building-apps/forms-data/add-grid/buffered-data.adoc

@@ -46,15 +46,14 @@ Yes, if you're not using <<../../security/protect-services#,method security>> or
 
 == Populating and Filtering the Grid
 
-Since the filtering happens in the service, you need to call the service whenever the filter string changes, and then call `setItems()` on the grid with the returned items:
+Since the filtering happens in the service, you need to call the service whenever the filter string changes, and then call `setItems()` on the grid's `ListDataView` with the returned items:
 
 [source,java]
 ----
 include::{root}/src/main/java/com/vaadin/demo/buildingapps/grid/BufferedGridView.java[tags=filtering,indent=0]
 ----
 
-There is one caveat with this approach: *selection is not preserved* between calls to `setItems()`. If you need to preserve selection, consider using a <<paginated-data#,paginated grid>> instead.
-// TODO Add link to guide about selection handling in grids
+The reason you're calling `ListDataView.setItems()` and not `Grid.setItems()` is that `Grid.setItems()` always creates a new data provider. This in turns clears the selection of the grid. If you want to preserve the selection, you need to update the existing data provider and that is what `ListDataView.setItems()` does.
 
 
 == Sorting

src/main/java/com/vaadin/demo/buildingapps/grid/BufferedGridView.java

@@ -32,8 +32,8 @@ public class BufferedGridView extends VerticalLayout {
 
         // tag::filtering[]
         // Update the grid whenever the text field changes
-        filterField.addValueChangeListener(e -> grid.setItems(
-                service.findItems(e.getValue())));
+        filterField.addValueChangeListener(e -> grid.getListDataView()
+                .setItems(service.findItems(e.getValue())));
         // end::filtering[]
 
         // Layout components