Table of Contents

Capability Policies and Overrides

Dock supports layered capability resolution for all core interaction flags:

  • CanClose
  • CanPin
  • CanFloat
  • CanDrag
  • CanDrop
  • CanDockAsDocument

This enables global policy defaults, per-dock policy tuning, and per-window exceptions.

Policy layers and precedence

Effective capability values are resolved in this order:

  1. Base dockable flag (IDockable.Can*)
  2. Root policy (IRootDock.RootDockCapabilityPolicy)
  3. Dock policy (IDock.DockCapabilityPolicy)
  4. Dockable override (IDockable.DockCapabilityOverrides)

Later layers override earlier layers when a value is set (bool? value is not null).

null means "inherit".

API surface

  • DockCapabilityPolicy (Dock.Model.Core)
  • DockCapabilityOverrides (Dock.Model.Core)
  • IRootDock.RootDockCapabilityPolicy
  • IDock.DockCapabilityPolicy
  • IDockable.DockCapabilityOverrides
  • DockCapabilityResolver for explicit evaluation
  • IDockManager.LastCapabilityEvaluation for diagnostics when validation is blocked by capability policy

Example

var root = factory.CreateRootDock();
root.RootDockCapabilityPolicy = new DockCapabilityPolicy
{
    CanFloat = false
};

var tools = factory.CreateToolDock();
tools.DockCapabilityPolicy = new DockCapabilityPolicy
{
    CanFloat = true
};

var explorer = factory.CreateTool();
explorer.DockCapabilityOverrides = new DockCapabilityOverrides
{
    CanFloat = false
};

In this example, floating is:

  • globally disabled at root,
  • re-enabled for the tool dock,
  • disabled again for one specific tool.

Validation and diagnostics

Dock validation (IDockManager) and core factory operations now use effective capability values.

When an operation is rejected by capability policy, IDockManager.LastCapabilityEvaluation provides:

  • evaluated capability,
  • source layer (Dockable, RootPolicy, DockPolicy, DockableOverride),
  • effective value and a diagnostic message.

UI behavior

Default Fluent menus and drag entry points use effective capability resolution, so blocked actions are hidden/disabled consistently with runtime validation.

Policies and overrides may remain null, including on docks created when floating a document. The built-in themes observe these optional values without logging null-path binding warnings. Replacing or clearing a policy updates the bindings; custom policies implementing INotifyPropertyChanged can also notify changes to individual capability properties.

Custom templates can use Avalonia's compiled bindings with the null-conditional ?. operator alongside the capability converters:

<MultiBinding xmlns="https://github.com/avaloniaui"
              xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
              xmlns:core="using:Dock.Model.Core"
              xmlns:converters="using:Dock.Avalonia.Converters"
              x:DataType="core:IDockable"
              x:CompileBindings="True"
              Converter="{x:Static converters:DockCapabilityConverters.CanDragMultiConverter}">
  <Binding />
  <Binding Path="CanDrag" />
  <Binding Path="DockCapabilityOverrides?.CanDrag" Mode="OneWay" />
  <Binding Path="((core:IDock)Owner)?.DockCapabilityPolicy?.CanDrag" Mode="OneWay" />
</MultiBinding>

For a dock data context, bind DockCapabilityPolicy?.CanDrag to observe its policy or ActiveDockable?.DockCapabilityOverrides?.CanDrag to observe its active dockable's overrides. The compiler validates these paths against the declared x:DataType; Avalonia owns their subscriptions and lifetime.

Avalonia 11.3.22 still logs a Value is null diagnostic when Owner itself is null in the interface-cast path above. Null policies and overrides on an existing owner are handled without warnings. Avalonia 12.1.3 includes the upstream null-conditional cast fix (#22174), so a null owner is also warning-free there. Dock leaves genuine binding errors visible rather than suppressing diagnostics.

Sample

DockXamlReactiveUISample includes:

  • root, tool-dock, and document-dock capability policy controls,
  • first generated item capability override controls,
  • live testing against items-source generated windows.
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