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Expansion and Programmatic Navigation

This guide focuses on hierarchical navigation and expansion control APIs.

Expand/Collapse APIs

HierarchicalTreeDataGridSource<TModel> provides:

  • Expand(IndexPath)
  • Collapse(IndexPath)
  • ExpandAll()
  • CollapseAll()
  • ExpandCollapseRecursive(Func<TModel, bool>)
  • ExpandCollapseRecursive(HierarchicalRow<TModel>, Func<TModel, bool>)

Example:

Source.Expand(new IndexPath(0));
Source.Expand(new IndexPath(0, 2));
Source.Collapse(new IndexPath(0, 1));

Predicate Expansion

Source.ExpandCollapseRecursive(model => model.Name.StartsWith("A"));

This is useful for search/filter style expansion.

Expansion Events

Lifecycle events on source:

  • RowExpanding
  • RowExpanded
  • RowCollapsing
  • RowCollapsed

Use them for telemetry, lazy loading markers, or command state updates.

Resolve Model by Path

if (Source.TryGetModelAt(new IndexPath(0, 1, 3), out var model))
{
    // model found
}

Use this for actions driven from saved IndexPath values.

Scroll to a Hierarchical Row

var path = new IndexPath(0, 1, 3);
Source.Expand(path[..^1]);

var rowIndex = Source.Rows.ModelIndexToRowIndex(path);
if (rowIndex >= 0)
    grid.RowsPresenter?.BringIntoView(rowIndex);

Parent/Child Navigation Helpers

IndexPath helpers:

  • parent: path[..^1]
  • child append: path.Append(childIndex)
  • relationships: IsAncestorOf, IsParentOf

Persist Expanded State

With HierarchicalExpanderColumn<TModel> use isExpandedSelector to bind expansion state to model property.

This is recommended when tree state should survive rebind/reload.

Troubleshooting

  • Feature behavior differs from expectations Cause: one or more options in this scenario are configured differently (source type, column options, sort/selection/edit state). Fix: compare your setup with the snippet in this article and verify runtime values on Source, Columns, and Selection.

  • Data changes are not visible in UI Cause: model or collection notifications are missing, or a replaced collection/source is not re-bound. Fix: ensure INotifyPropertyChanged/INotifyCollectionChanged flow is active and reassign Source after replacing underlying collections.

API Coverage Checklist