Theme Usage

TreeDataGrid ships with two theme entry files:

Themes/Generic.axaml
Themes/Fluent.axaml

Include Pattern

For Fluent applications, include Fluent theme and TreeDataGrid Fluent styles:

<Application.Styles>
  <FluentTheme/>
  <StyleInclude Source="avares://Avalonia.Controls.TreeDataGrid/Themes/Fluent.axaml"/>
</Application.Styles>

Fluent vs Generic

Fluent.axaml includes Generic.axaml, then overrides selected resource keys with Fluent system colors.

In source, this is implemented via StyleInclude Source="/Themes/Generic.axaml" inside Fluent.axaml.

This means:

Generic defines control templates and baseline resources.
Fluent keeps templates and replaces values for key brushes.

Theme Dictionaries

Both files define Default and Dark dictionaries for TreeDataGrid keys.

Key groups include:

grid/header/selection brushes
sort icon geometries
expander chevron geometries
control themes for grid primitives and cells

Control Themes Defined in Generic

Generic.axaml defines ControlTheme entries for:

TreeDataGrid
TreeDataGridColumnHeader
TreeDataGridRow
TreeDataGridCheckBoxCell
TreeDataGridExpanderCell
TreeDataGridTextCell
TreeDataGridTemplateCell

It also defines a keyed ToggleButton theme for the expander chevron.

Dynamic vs Static Resources

The templates use DynamicResource for most override points (TreeDataGrid...Brush keys), so app-level overrides propagate without replacing full control themes.

Troubleshooting

Header/cell colors do not change after overriding key Cause: wrong key name or override is defined in an unreachable resource scope. Fix: verify exact key spelling and move override to Application.Resources to confirm reachability.
Theme looks incomplete Cause: Grid is loaded without TreeDataGrid style include. Fix: include TreeDataGrid Fluent.axaml or Generic.axaml explicitly.