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Indexing and Addressing

TreeDataGrid distinguishes between model indexes and visible row indexes.

Understanding this difference is critical for selection, expansion, sorting, and drag/drop.

IndexPath: Hierarchical Model Address

IndexPath identifies a model row in the source hierarchy.

Examples:

  • first root item: new IndexPath(0)
  • second child of first root: new IndexPath(0, 1)
  • first grandchild under that child: new IndexPath(0, 1, 0)

Conveniences:

  • implicit conversion from int for flat roots (IndexPath p = 3;)
  • IndexPath.Unselected for empty/no selection
  • Append(int) to build deeper paths

CellIndex: Cell Address

CellIndex combines:

  • ColumnIndex (int)
  • RowIndex (IndexPath)

It is used by cell selection APIs.

Example:

var cell = new CellIndex(columnIndex: 2, rowIndex: new IndexPath(0, 1));

Model Index vs Visible Row Index

IndexPath addresses model position. Visible row index addresses current on-screen order.

They can differ when:

  • hierarchical rows are collapsed/expanded
  • sorting is active
  • virtualization and realization are in effect

Row collections expose conversion APIs:

  • IRows.ModelIndexToRowIndex(IndexPath)
  • IRows.RowIndexToModelIndex(int)

Practical Rules

  • Persist selections using IndexPath (model index), not visible row index.
  • Convert to visible row index only when targeting UI operations (BringIntoView, TryGetRow).
  • After sorting or hierarchy changes, recalculate visible row indexes.

Working with Hierarchy Paths

Use IndexPath helpers when traversing:

  • parent path: path[..^1]
  • direct child path: path.Append(childIndex)
  • relationship checks:
    • parent.IsAncestorOf(child)
    • parent.IsParentOf(child)

Example: Select and Scroll a Hierarchical Row

var modelIndex = new IndexPath(0, 1, 0);
Source.RowSelection!.SelectedIndex = modelIndex;

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

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.

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