Expand and Collapse

Programmatic tree operations live on HierarchicalTreeDataGridSource<TModel>.

Basic Operations

Source.Expand(new IndexPath(0));
Source.Collapse(new IndexPath(0));
Source.ExpandAll();
Source.CollapseAll();

You can also expand or collapse recursively:

Source.ExpandCollapseRecursive(x => x.IsExpandedByDefault);

Row Events

Hierarchical sources raise:

RowExpanding
RowExpanded
RowCollapsing
RowCollapsed

These events now use TreeDataGridRowModelEventArgs:

Source.RowExpanded += (_, e) =>
{
    var model = (Person?)e.Row.Model;
    var path = e.Row.ModelIndexPath;
};

When to Use This API

Use the Source workflow when you need programmatic control over the expansion state. Declarative ItemsSource grids are useful for markup-driven tree layouts, but the explicit source remains the path for advanced runtime tree management.