Unity’s runtime uses a specialized assembly loading and management system to support code reload. The UAC (Unity API Compatibility) analyzer flags several reflection APIs that are or will soon become incompatible with Unity’s assembly lifecycle.
| Warning code | Incompatible .NET API | Compatible Unity alternative |
|---|---|---|
UAC005 |
AppDomain.GetAssemblies This standard .NET API returns all loaded assemblies from all AssemblyLoadContexts (ALCs), including those that are in an unloading state. Using these stale assembly references can cause TypeLoadException, NullReferenceException, memory leaks, or Editor crashes. Unity provides CurrentAssemblies.GetLoadedAssemblies which only returns assemblies that are currently active and valid within Unity’s managed environment, ensuring safe enumeration during all Editor states. |
CurrentAssemblies.GetLoadedAssemblies |
UAC006 |
Certain methods and events in the AppDomain class. These AppDomain events are not properly triggered or managed in Unity’s assembly lifecycle system. Subscribing to these events can result in handlers that are never called, or called at incorrect times during code reloads, leading to memory leaks or crashes. For assembly unloading notifications, use Unity’s LifeCycle APIs. |
Unity’s LifeCycle APIs. |
UAC007 |
Assembly.Location Unity loads many assemblies from memory streams rather than directly from disk to avoid file locking. For these assemblies, the Assembly.Location property returns an empty string, breaking code that relies on file paths for loading dependencies or resources. The Assembly.GetLoadedAssemblyPath extension method provided by Unity tracks and returns the original source path reliably, working correctly for both disk-loaded and stream-loaded assemblies. |
Assembly.GetLoadedAssemblyPath |
UAC020 |
Assembly.LoadFile / Assembly.LoadFrom These methods load assemblies outside of Unity’s assembly management system. This bypasses Unity’s dependency tracking, prevents proper unloading during script recompilation and code reloads, and can cause assembly version conflicts. Use CurrentAssemblies.LoadFromPath instead, which integrates with Unity’s assembly lifecycle so assemblies can be properly tracked, reloaded, and unloaded when needed. |
CurrentAssemblies.LoadFromPath |
UAC023 |
BinaryFormatter This serializer is deprecated in modern .NET due to critical security vulnerabilities and will not be supported in Unity’s runtime environment. Use Unity’s built-in serialization system, JsonUtility, or DataContract instead. |
Unity serialization, JsonUtility, DataContract
|
The following table provides examples of incompatible code snippets and what they can be replaced with:
| Incompatible code | Replacement | Namespace |
|---|---|---|
AppDomain.CurrentDomain.GetAssemblies() |
CurrentAssemblies.GetLoadedAssemblies() |
UnityEngine.Assemblies |
AppDomain.CurrentDomain.DomainUnload |
[OnAssemblyUnloading] |
Unity.Scripting.LifecycleManagement |
assembly.Location |
assembly.GetLoadedAssemblyPath() |
UnityEngine |
Assembly.LoadFile(path) |
CurrentAssemblies.LoadFromPath(path) |
UnityEngine.Assemblies |