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Selection Models

TreeDataGrid supports two primary selection modes:

  • row selection
  • cell selection

The active behavior comes from ITreeDataGridSource.Selection.

Default Behavior

If you do not assign Selection explicitly:

  • sources create a row selection model by default
  • selection is single-select by default

This makes basic keyboard/mouse selection work immediately.

Row Selection Model

Main API:

  • TreeDataGridRowSelectionModel<TModel>
  • ITreeDataGridRowSelectionModel<TModel>

Common operations:

  • set SelectedIndex (IndexPath)
  • inspect SelectedIndexes, SelectedItem, SelectedItems
  • enable multi-select via SingleSelect = false

Example:

Source.RowSelection!.SingleSelect = false;
Source.RowSelection.SelectedIndex = new IndexPath(0, 1);

Cell Selection Model

Main API:

  • TreeDataGridCellSelectionModel<TModel>
  • ITreeDataGridCellSelectionModel<TModel>

Common operations:

  • set SelectedIndex (CellIndex)
  • inspect SelectedIndexes
  • select ranges via SetSelectedRange(...)

Example:

Source.Selection = new TreeDataGridCellSelectionModel<Person>(Source)
{
    SingleSelect = false,
};

Switching Modes at Runtime

Switch by replacing Source.Selection:

if (useCellSelection)
    Source.Selection = new TreeDataGridCellSelectionModel<Person>(Source);
else
    Source.Selection = new TreeDataGridRowSelectionModel<Person>(Source);

Requirement: assigned selection model must point to the same Items source.

Base Contracts and Advanced Behavior

Core contracts:

  • ITreeSelectionModel
  • ITreeDataGridSelection
  • ITreeDataGridSelectionInteraction

Advanced events from selection base model:

  • SelectionChanged
  • IndexesChanged
  • SourceReset

SourceReset is important when source collections raise reset notifications.

Anchors and Ranges

For keyboard/range logic, selection models track:

  • AnchorIndex
  • RangeAnchorIndex

This supports shift-range operations and consistent keyboard navigation behavior.

Practical Recommendations

  • Prefer row selection for list-style workflows and commands on full records.
  • Prefer cell selection for spreadsheet-like editing.
  • Persist model addresses (IndexPath, CellIndex) rather than visible row numbers.

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