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Dependency Injection#

This document assumes you're already familiar with the Dependency Injection (DI) pattern. If not, the frameworks listed below describe the pattern in their documentation.

TLDR, How to enable#

dotnet add package CommandDotNet.IoC.MicrosoftDependencyInjection

Install-Package CommandDotNet.IoC.MicrosoftDependencyInjection

Enable MicrosoftDependencyInjection with
appRunner.UseMicrosoftDependencyInjection(...)

dotnet add package CommandDotNet.IoC.Autofac

Install-Package CommandDotNet.IoC.Autofac

Enable Autofac with
appRunner.UseAutofac(...)

dotnet add package CommandDotNet.IoC.SimpleInjector

Install-Package CommandDotNet.IoC.SimpleInjector

Enable SimpleInjector with
appRunner.UseSimpleInjector(...)

No package required

Enable the custom resolver with
appRunner.UseDependencyResolver(myCustomContainer, ...)

Configuration options#

When a resolver is registered, it will be used to resolve instances for

  • command classes using IDependencyResolver.Resolve
  • IArgumentModel classes using IDependencyResolver.TryResolve.

DI containers have different behaviors for Resolve and TryResolve. In most cases, Resolve will throw an exception if an instance isn't registered. Some containers, like MicrosoftDependencyInjection, will return null instead. When TryResolve is used or Resolve returns null, CommandDotNet will attempt to instantiate an instance.

UseDependencyResolver contains the following configuraion parameters:

public static AppRunner UseDependencyResolver(
    ...
    Func<CommandContext, IDisposable> runInScope = null,
    ResolveStrategy argumentModelResolveStrategy = ResolveStrategy.TryResolve,
    ResolveStrategy commandClassResolveStrategy = ResolveStrategy.Resolve,
    bool useLegacyInjectDependenciesAttribute = false
}
  • runInScope: if provided, the scope will be created at the beginning of the run and disposed at the end
  • argumentModelResolveStrategy: the ResolveStrategy used to resolve IArgumentModel classes.
  • commandClassResolveStrategy: the ResolveStrategy used to resolve command classes.
  • useLegacyInjectDependenciesAttribute: when true, resolve instances for command class properties marked with [InjectProperty]. This feature is deprecated and may be removed with next major release.

These parameters also exist for the AutoFac, MicrosoftDependencyInjection and SimpleInjector packages

Custom Resolvers#

To implement another 3rd party resolver, follow the example for one of the existing ones. Submit a PR so we can keep it up-to-date for you.

To implement your own custom resolver, implement the IDependencyResolver. See the TestDependencyResolver for an example.

Registering all command classes#

Use appRunner.GetCommandClassTypes() to get all the command class types that could be instantiated from the AppRunner.

private static void RegisterSimpleInjector(AppRunner appRunner)
{
    var container = new SimpleInjector.Container();
    foreach(Type type in appRunner.GetCommandClassTypes())
    {
        container.Register(type);
    }
    appRunner.UseSimpleInjector(container);
}