Primitives Overview

This article covers the low-level visual primitives used by TreeDataGrid templates.

Primitive Roles

TreeDataGridRow: row container and row-level interaction surface.
TreeDataGridCell: base for all cell visuals and edit lifecycle.
TreeDataGridTextCell: text rendering and text edit presentation.
TreeDataGridCheckBoxCell: bool/tri-state cell UI.
TreeDataGridTemplateCell: template-driven cell with editing template support.
TreeDataGridExpanderCell: indentation and expand/collapse affordance.
TreeDataGridColumnHeader: header visual with sorting/resizing behavior.

Important State and Pseudoclasses

TreeDataGridRow: :selected
TreeDataGridCell: :selected, :editing
TreeDataGridColumnHeader: :resizable

These are the key hooks for high-performance styling.

Editing Lifecycle at Cell Level

TreeDataGridCell manages:

begin edit (gesture-dependent)
commit (EndEdit) and cancel (CancelEdit)
value synchronization to cell model
CellValueChanged signal through owner grid

Begin-edit behavior is controlled by BeginEditGestures.

Styling Example

<Style Selector="TreeDataGridRow:selected">
  <Setter Property="Background" Value="#1F3A5F"/>
</Style>

<Style Selector="TreeDataGridCell:editing">
  <Setter Property="Background" Value="#FFF6D5"/>
</Style>

<Style Selector="TreeDataGridColumnHeader:resizable">
  <Setter Property="Cursor" Value="SizeWestEast"/>
</Style>

Interaction Notes

TreeDataGridRow detects pointer movement threshold and can start row drag.
TreeDataGridExpanderCell mirrors expansion state from IExpanderCell.
TreeDataGridTemplateCell manages focus transitions for editing content.

Troubleshooting

Editing template loses focus too early Cause: editing content is hosted in popup or descendant focus chain not tracked by custom template.
Checkbox cell value appears stale Cause: model does not implement expected property change notifications.
Row drag starts unexpectedly Cause: pointer movement exceeds drag threshold while selection gestures are active.