WpfTreeGrid

A tree grid for WPF: hierarchical rows with expand/collapse, sorting, Excel-style column filters and cell editing, built on the standard DataGrid. Column resizing and reordering, virtualization and selection come from WPF itself.

Children sort under their parent	Excel-style column filter

Usage

<tg:TreeDataGrid xmlns:tg="clr-namespace:WpfTreeGrid;assembly=WpfTreeGrid"
                 ItemsSource="{Binding Roots}"
                 ChildPropertyName="Children"
                 ExpandStateMappingName="IsExpanded"
                 AutoExpandMode="RootNodesExpanded"
                 AllowFiltering="True" AllowEditing="True" SelectionMode="Extended">
    <tg:TreeDataGrid.Columns>
        <tg:TreeGridTextColumn MappingName="Name" ColumnSizer="Star" />
        <tg:TreeGridCheckBoxColumn MappingName="IsSelected" HeaderText="Use" AllowFiltering="False" />
        <tg:TreeGridNumericColumn MappingName="Mass" HeaderText="Mass (kg)" NumberDecimalDigits="3" />
    </tg:TreeDataGrid.Columns>
</tg:TreeDataGrid>

The expander goes in the first column, or in the column named by ExpanderColumn. Rows are the bound items themselves, so columns and styles bind as in any DataGrid.

API at a glance

Area	Members
Grid	ChildPropertyName, ParentPropertyName + SelfRelationRootValue (flat lists), ExpandStateMappingName, AutoExpandMode, ExpanderColumn, FilterLevel, AllowFiltering, AllowEditing, AllowSorting, AllowResizingColumns, AllowDraggingColumns, ShowRowHeader, HeaderRowHeight, ColumnSizer, RecordContextMenu, BindableSelectedItems
Columns	TreeGridTextColumn, TreeGridNumericColumn, TreeGridDateTimeColumn, TreeGridCheckBoxColumn, TreeGridTemplateColumn, all with MappingName, HeaderText, AllowEditing, AllowSorting, AllowFiltering, AllowResizing, IsHidden, MinimumWidth, MaximumWidth, ColumnSizer; ITreeGridColumn to treat them alike
Tree	View (Nodes, Filter, RefreshFilter()), GetNode, ExpandNode, CollapseNode, ExpandAllNodes, CollapseAllNodes, ExpandToLevel, TreeNode (Item, ChildNodes, ParentNode, Level, IsExpanded), NodeExpanding/NodeExpanded/NodeCollapsing/NodeCollapsed
Sorting and filters	SortColumnDescriptions, SortBy, ClearSort; per column FilterPredicates (FilterPredicate with FilterType, FilterValue, PredicateType, FilterBehavior), ClearFilter, ClearFilters, FilterChanged
Cell selection and editing	With SelectionUnit="Cell": SelectCell(s), UnselectCell(s), ClearSelections, MoveCurrentCell, GetSelectedCells, CurrentCellInfo, CurrentCellBeginEdit (cancelable), CurrentCellEndEdit, EditTrigger, SelectionController.CurrentCellManager (BeginEdit, EndEdit, CurrentCell.IsEditing), TreeGridIndexResolver + RowColumnIndex (header row 0, visible rows from 1)

Column properties are dependency properties, so they can be bound, and columns see the grid's DataContext, so IsHidden="{Binding ShowSomething}" works. A column's Width reads as pixels (double, NaN when sized by ColumnSizer), and ItemsSource reads back as the bound collection. The grid-level Allow* properties are plain CLR properties over the DataGrid ones. Set them as attributes; to bind, use the underlying property (IsReadOnly, CanUserSortColumns and so on).

Behaviour notes

• Sorting: strings sort naturally ("Part2" before "Part10"), children stay under their parent, and a child added under a sorted column lands in sorted position.
• Filter levels: FilterLevel.Extended also sees descendants that were never expanded.
• Auto-generated columns: AutoGenerateColumns defaults to false, because generated DataGrid columns can't host the expander.
• Filter events: column filters apply immediately when predicates are added; FilterChanged is raised only for changes made in the filter popup.
• Editing: the value is written when the cell commits (Enter, Tab, another cell), and each committed cell is written straight away, with no row-level edit. Escape or EndEdit(false) puts the old value back. CurrentCellEndEdit comes after the value is in the row. A grid with AllowEditing="False" locks every column, and a cell bound to a property without a setter doesn't open an editor.
• Selection: the selected cells and the current cell stay put when rows expand or sort.

Styling

The default look is a plain, light grid. Each part is a resource under a key on TreeDataGrid:

Key	What
ColumnHeaderStyleKey	Header with sort chevron and filter button
CellStyleKey	Cell with grey selection and current-cell border
ExpanderStyleKey	The ⊞/⊟ toggle
LineBrushKey, SelectionBrushKey, FilteredBrushKey	Colours

To replace a part, define a resource under the same key in app resources. To adjust one instead, base a style on it:

<Style TargetType="DataGridColumnHeader" BasedOn="{StaticResource {x:Static tg:TreeDataGrid.ColumnHeaderStyleKey}}">
    <Setter Property="FontWeight" Value="SemiBold" />
</Style>

The filter button lives in the header style. A header style that is not based on ColumnHeaderStyleKey loses it.

How it works

TreeModel (in WpfTreeGrid.Core, no WPF dependency) walks the items through a TreeSchema and exposes the visible rows as TreeRows. Every change recomputes the visible rows in one pass and diffs them against the current list. Expand/collapse, observable child collections, sorting and filtering all go through that path. Small changes raise single-item Add/Remove; large ones raise a single Reset (TreeRows.MaxIncrementalChanges). Items are tracked by reference, so the same instance must not appear twice in a tree.

Layout

Project	Target	Contents
src/WpfTreeGrid.Core	net8.0	Tree model, sorting and filter predicates; no WPF dependency
src/WpfTreeGrid	net8.0-windows	TreeDataGrid, the columns, the filter popup and the theme
tests/*		xUnit tests: pure logic, plus STA tests of the control
samples/WpfTreeGrid.Demo		A 10,000-row demo
docs/capture		Renders the demo offscreen into the README images

Licence

MIT, see LICENSE.