[TreeGrid] Should refresh only visible items instead of triggering full data reset where possible

[vursen]

Description

setDropMode, setDragFilter, setPartNameGenerator, and many other TreeGrid methods call dataCommunicator.reset to re-render items, typically to update certain attributes. This operation is effectively equivalent to refreshAll and triggers a full reset of the hierarchy, which causes an annoying scroll position reset on the client-side.

In cases where the grid's hierarchy isn't expected to change – which is true for all the mentioned methods – it should be enough to simply call refreshItem for items that are currently visible.

Expected outcome

The Flow framework should provide an API to retrieve items that are currently in the viewport. With this API, the Flow component could call refreshItem for visible items instead of doing a full reset.

Minimal reproducible example

This issue has become especially problematic after #6339 added a data communicator reset to setDropMode. When setting the drop mode dynamically on drag start, the scroll can now jump to a quite random position, significantly disrupting the dragging process.

@Route("tree-grid-bug")
public class TreeGridBugPage extends Div {
    public TreeGridBugPage() {
        TreeGrid<String> treeGrid = new TreeGrid<>();
        treeGrid.addHierarchyColumn(item -> item);
        treeGrid.setRowsDraggable(true);

        treeGrid.setDragFilter(item -> item.startsWith("Child-"));
        treeGrid.setDropFilter(item -> item.startsWith("Child-"));

        TreeData<String> treeData = new TreeData<>();
        for (int i = 0; i < 100; i++) {
            String item = "Root-" + i;
            treeData.addItem(null, item);
            for (int j = 0; j < 10; j++) {
                treeData.addItem(item, "Child-" + i + "-" + j);
            }
        }
        treeGrid.setTreeData(treeData);

        treeGrid.addDragStartListener(e -> {
            treeGrid.setDropMode(GridDropMode.ON_TOP_OR_BETWEEN);
        });
        treeGrid.addDropListener(e -> {
            treeGrid.setDropMode(null);
        });

        add(treeGrid);
    }
}

Steps to reproduce

Screen.Recording.2024-10-11.at.15.45.42.mov

Environment

Vaadin version(s): 24.5 and earlier
OS: Mac OS

Browsers

No response

[vursen]

• fix: do not trigger data communicator reset when no filters #6712
• fix: revert static drop mode for tree grid docs#3786

We can consider reverting these PRs when the issue is fixed.

[vursen]

I'm attaching the branch with my experiment to implement such an API in Flow:

https://github.com/vaadin/flow/compare/get-requested-range-items-method

The solution isn't complete. The API can currently return more items than necessary because DataCommunicator keeps expanded items in the key mapper after they have been visited once. Some additional logic is needed to filter out such items when they are out of the requested range.