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Hierarchical Expander Column Guide

HierarchicalExpanderColumn<TModel> wraps another column and adds tree expansion affordances.

Use it only with HierarchicalTreeDataGridSource<TModel>.

Basic Constructor

new HierarchicalExpanderColumn<Person>(
    inner: new TextColumn<Person, string>("Name", x => x.Name),
    childSelector: x => x.Children)

Parameters:

  • inner: how the column content is rendered
  • childSelector: returns children for each model

Advanced Constructor Selectors

You can provide optional selectors to optimize behavior and persist expansion state.

new HierarchicalExpanderColumn<FileNode>(
    inner: new TemplateColumn<FileNode>("Name", "FileNameCell", "FileNameEditCell"),
    childSelector: x => x.Children,
    hasChildrenSelector: x => x.HasChildren,
    isExpandedSelector: x => x.IsExpanded)

hasChildrenSelector avoids expensive child materialization for expander visibility checks.

isExpandedSelector syncs UI expanded state with model property.

Sorting and Width

The expander column delegates width and sorting behavior to its inner column.

That means:

  • sorting capability is inherited from inner.GetComparison(...)
  • width changes operate on inner column layout

Common Pitfalls

  • Creating hierarchical source without an expander column causes runtime errors.
  • Adding more than one expander column is not allowed by source.
  • Removing/replacing/moving expander column after add is not allowed.

Best Practices

  • Use TemplateColumn as inner column for rich file/tree visuals.
  • Provide hasChildrenSelector when child loading is lazy or expensive.
  • Bind isExpandedSelector if expanded state should persist across refresh/rebind.

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