Avalonia.Native

This project implements the macOS native platform backend for Avalonia using Objective-C++ and COM (Component Object Model) interfaces.

COM Reference Management

This codebase uses COM for cross-boundary object lifetime management. COM types are typically prefixed with IAvn (interfaces) or Avn (implementations). All COM objects ultimately derive from IUnknown and use reference counting (AddRef/Release).

No raw COM pointer should ever be stored in class fields, instance variables, closures, or containers. Raw COM pointers are only acceptable as function parameters and local variables with the lifetime of the current function call.

COM Return Value Convention

By convention, any COM interface reference returned from a COM call has its reference counter incremented — it is the caller's responsibility to release it. With the IFoo* GetFoo() pattern it is hard to track this correctly, so all methods in avn.idl should use the out-parameter pattern instead:

// WRONG — easy to leak or forget Release:
IFoo* GetFoo();

// CORRECT — use HRESULT + out-parameter:
HRESULT GetFoo(IFoo** ppv);

Smart pointer types

Objective-C Objects

For Objective-C objects, reference counting is provided by the compiler. Objective-C pointers look like raw pointers, however every NSObject* reference is properly ref-counted by ARC (Automatic Reference Counting). No manual wrapping is needed for NSObject* fields.

COM Smart Pointer Types

All retained COM references must use one of the following wrappers defined in inc/comimpl.h:

ComPtr<T> — Owning Reference

Use for any COM pointer that the holder needs to keep alive.

ComPtr<IAvnWindow> _window; // correct
IAvnWindow* _window;        // WRONG — raw COM pointer in a field

ComObjectWeakPtr<T> — Non-Owning Weak Reference

Use for intentional non-owning references to ComObject-derived objects (internal implementations). Allows safely referencing COM objects without extending their lifetime.

ComObjectWeakPtr<WindowBaseImpl> _parent; // correct
WindowBaseImpl* _parent;                  // WRONG

Access weak references with tryGet(), which returns a ComPtr<T> (null if the object was destroyed):

auto parent = _parent.tryGet();
if (parent) {
    parent->DoSomething();
}

ComStaticPtr<T> — Process-Lifetime Static Reference

Use for static/global COM singletons that must live for the entire process lifetime. Intentionally does not Release in its destructor to avoid crashes during app teardown.

static ComStaticPtr<IAvnGlDisplay> GlDisplay; // correct
static IAvnGlDisplay* GlDisplay;              // WRONG

Assign via set():

GlDisplay.set(comnew<AvnGlDisplay>());

comnew<T>(args...) — COM Object Factory

A convenience template similar to std::make_shared. Creates a new COM object and returns it wrapped in a ComPtr<T> with correct ownership (no double-AddRef):

// Instead of:
ComPtr<Cursor> cursor(new Cursor(nsCursor), true);

// Write:
ComPtr<Cursor> cursor = comnew<Cursor>(nsCursor);

This works because new T() on a ComObject-derived type starts with refcount=1, and comnew wraps it in a ComPtr that takes ownership without an additional AddRef.