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Common Errors

EServiceAlreadyRegistered​

Symptom: Exception raised at startup or at a call to Singleton<T>, SingletonLazy<T>, SingletonInterface<I,T>, Factory<T>, or AddInject.

Message: Class <T> registered! or Interface <T> already registered! or Injector <tag> already registered!

Cause: The same class, interface GUID, or tag was registered more than once. This commonly happens when:

  • A unit's initialization block is executed multiple times (e.g., loaded from two different BPL packages that both include the unit).
  • You have a conditional branch that registers a service on multiple code paths.

Fix:

  • Guard registrations with if not FRepositoryReference.ContainsKey(T.ClassName) then ... in ambiguous paths.
  • Use AddInstance<T> when you control the construction and want to overwrite an existing registration (but note this also raises if already registered — use Remove<T> first if needed).

EServiceNotFound​

Symptom: Exception raised at GetInterface<I>.

Message: Interface <GUID-string> not found!

Cause: GetInterface<I> was called before the interface was registered, or the interface I does not have a GUID, or the correct unit was not in the uses clause causing initialization to never run.

Fix:

  1. Ensure the unit that contains GetInjector.SingletonInterface<I, T> is in the uses clause of either the .dpr or a unit transitively referenced at startup.
  2. Confirm the interface I has a GUID attribute (['{...}']).
  3. Use GetInjector.GetInstances to inspect what is actually registered.

ECircularDependency​

Symptom: Exception during Get<T> or GetInterface<I>.

Message: Circular dependency detected: TServiceA -> TServiceB -> TServiceA

Cause: Two (or more) services depend on each other, forming a cycle. The dependency stack detects this when the same service name appears twice on the stack.

Fix: See Circular Dependency Detection — How to fix.

Get<T> returns nil unexpectedly​

Symptom: GetInjector.Get<T> returns nil but no exception is raised.

Cause: Get<T> returns nil (not raises) when the service is not found. Either:

  • The service was not registered.
  • The registration unit's initialization block did not execute (unit not referenced in uses).
  • The tag passed does not match the registration tag.

Fix:

  1. Add a nil check and log: if not Assigned(LSvc) then raise Exception.Create('TMyService not registered').
  2. Confirm the registration unit is in the uses clause.
  3. Enable logging (EnableLogging) and watch for Get Service: lines.

RTTI: class has no parameterless Create constructor​

Symptom: Access violation or RTTI exception during auto-wired lazy resolution.

Cause: _ResolverParams calls TRttiType.GetMethod('Create') and attempts to invoke it with auto-resolved parameters. If the class has no Create method visible to RTTI (e.g., inherited from TInterfacedObject with no public override), the method may not be found.

Fix: Declare an explicit constructor Create; in the class so RTTI can locate and invoke it. Alternatively, supply AOnConstructorParams to bypass auto-wiring:

GetInjector.SingletonLazy<TMyClass>(
  nil, nil,
  function: TConstructorParams
  begin
    Result := []; // no params
  end
);

Package-lock.json mismatch (documentation build only)​

Symptom: npm ci fails in the CI workflow with npm error Invalid: lock file's <package> errors.

Cause: package.json was updated but package-lock.json was not regenerated.

Fix: Run npm install locally inside docs-src/ and commit the updated package-lock.json.

Logging shows [Injector4D] prefix instead of [InjectContainer]​

Symptom: Log messages contain [Injector4D] in the prefix.

Cause: The _Log method in Inject.pas uses a hardcoded prefix '[Injector4D]'. This is the internal code name; the public framework name is InjectContainer.

Fix: This is cosmetic only and does not affect functionality. The prefix [Injector4D] is hardcoded in TInject._Log (Inject.pas) and has not been changed to [InjectContainer] in the current source.