atomui-resource-lifecycle

name	atomui-resource-lifecycle
description	Use when changing AtomUI or Avalonia resource bindings, DynamicResource, TokenResourceBinder, non-Visual AvaloniaObject lifecycle, IResourceHost/IThemeVariantHost, owner/container attach cleanup, or investigating memory leaks and retained controls.

AtomUI Resource Lifecycle

Overview

Resource lifecycle correctness is a hard boundary, not a performance optimization. Any object that subscribes, binds, attaches, caches, or enters an owner/container lifecycle must define the release event before the acquire call is accepted.

The Gallery rule is strict: after navigation settles, old ShowCases must not remain alive unless a feature explicitly owns a cache and documents its eviction policy.

DynamicResource Scoped Host Rule

A non-Visual AvaloniaObject must not carry DynamicResource or token-resource bindings unless it owns or is attached to a scoped IResourceHost with a verified release path.

Violations block merge because they can root an entire Gallery ShowCase through Application.ResourcesChanged.

Why This Leaks

DynamicResourceExpression chooses its resource host in this order:

1. If the binding target implements IResourceHost, use the target.
2. Otherwise use the XAML anchor / provider owner.
3. Subscribe to the selected host's ResourcesChanged, and to ActualThemeVariantChanged when the host is an IThemeVariantHost.

This behavior has been verified against the currently resolved framework dependency and AtomUI leak regressions. Revalidate it after dependency upgrades; do not copy an external version, local source path, or line number into AtomUI's long-term lifecycle contract.

If the target is a non-Visual AvaloniaObject and does not implement IResourceHost, the host can fall back to Application. The leak chain then becomes:

Application.ResourcesChanged
  DynamicResourceExpression
    ValueStore
      non-Visual AvaloniaObject
        owner/header/container
          Gallery ShowCase visual tree

This exact pattern leaked DataGridColumn, DataGridColumnGroupItem, and NavMenuNode. Full case study: docs/engineering/avalonia-dynamic-resource-memory-leak-case-study.md.

Required Patterns

Owner-based objects, such as DataGridColumn:

• Implement IResourceHost and IThemeVariantHost on the non-Visual object.
• TryGetResource(...) queries the scoped owner first, then falls back to Application.Current.
• Owner changes unsubscribe the old owner before assigning/subscribing the new owner.
• Owner ResourcesChanged and ActualThemeVariantChanged are forwarded through the object.
• Owner attach/detach raises ResourcesChanged so dynamic resources republish.

Container-driven data nodes, such as NavMenuNode:

• Do not store a permanent last-container reference.
• Attach through an API that returns IDisposable.
• Store the disposable in the same owner/container CompositeDisposable as the node bindings.
• Release through ClearContainerForItemOverride, detach, re-template, unregister, or owner disposal.
• If multiple temporary attachments are possible, use attachment counting or an equivalent scoped token.

Global token bindings:

• Do not create TokenResourceBinder.CreateGlobalTokenBinding(...) in constructors by default.
• Create global bindings on first real use, such as first open/show.
• Dispose the returned binding on close, unregister, detach, owner disposal, or the matching clear path.

Forbidden Patterns

• target[!SomeProperty] = new DynamicResource... on a non-Visual AvaloniaObject that is not a scoped IResourceHost.
• Constructor-time TokenResourceBinder.CreateGlobalTokenBinding(...) with no explicit release path.
• Relying on Gallery route reset, DataContext clearing, or visual cleanup to break a global resource subscription.
• Replacing dynamic resources with static values only to avoid a leak. That breaks theme/token behavior instead of fixing lifecycle.
• Permanent owner/container references used only to keep resource lookup working.

Required Tests

Every fix or new non-Visual dynamic-resource target needs lifecycle and resource behavior coverage:

• WeakReference test: dynamic resource does not root an otherwise unreferenced target after GC.
• Owner resource test: target uses scoped owner resources before falling back to Application.
• Resource update test: owner/application resource updates still republish values.
• Gallery object-count test when applicable: after random navigation, only the current ShowCase remains alive.

The WeakReference test must simulate the XAML DynamicResourceExtension anchor shape. Hand-setting a property or using only static values does not reproduce the Application-root leak.

Review Trigger

Before approving changes in this area, scan for:

rg "DynamicResource|CreateGlobalTokenBinding|IResourceHost|IThemeVariantHost" --type cs src/ controlgallery/
rg "class .*: AvaloniaObject" --type cs src/
rg "ResourcesChanged \\+|ActualThemeVariantChanged \\+|CreateGlobalTokenBinding" --type cs src/ controlgallery/

Any non-Visual AvaloniaObject with dynamic resource/token binding and no scoped host lifecycle is a blocker.

Memory Validation

Use object counts, not RSS alone:

• Current ShowCase count should settle to 1 after navigation.
• Old ShowCaseItem, DataGridColumn, NavMenuNode, and DynamicResourceExpression counts must not grow monotonically across random navigation.
• RSS can have load peaks; persistent old object graphs are the leak signal.