Can I mix dynamic and singleton types in MvvmCross dependency injection

Understanding Dependency Injection in MvvmCross

MvvmCross provides a simple and lightweight dependency injection (DI) container. You can register classes and interfaces in the container using multiple patterns, including singleton and dynamic registrations.

Singleton Registration

Singletons are useful when you want to ensure that only one instance of a class is created throughout the application's lifetime. In MvvmCross, you can register a singleton using the `Mvx.IoCProvider.RegisterSingleton` or `Mvx.IoCProvider.ConstructAndRegisterSingleton` methods. For example:

csharp
Mvx.IoCProvider.RegisterSingleton(new Foo());

or

csharp
Mvx.IoCProvider.ConstructAndRegisterSingleton();

Every time you resolve `IFoo`, you will get the same instance of `Foo`.

Dynamic Registration

Dynamic registration creates a new instance of the class every time it is resolved. You can register a dynamic instance using the `Mvx.IoCProvider.RegisterType` method. For example:

csharp
Mvx.IoCProvider.RegisterType();

Each call to `Mvx.IoCProvider.Resolve()` will return a new instance of `Foo`.

Mixing Dynamic and Singleton Types

If you want to mix dynamic and singleton types, you can use constructor injection with a factory pattern for dynamic instances. Here's an example:

Using Constructor Injection with a Factory

Suppose you have a singleton class `FooSingleton` that needs to use a dynamic instance of `Bar`. You can achieve this by injecting a factory for `Bar` instead of `Bar` itself:

csharp
public class FooSingleton : IFooSingleton
{
    private readonly IFactory _barFactory;

    public FooSingleton(IFactory barFactory)
    {
        _barFactory = barFactory;
    }

    public void DoFoo()
    {
        var bar = _barFactory.Create();
        bar.DoStuff();
    }
}

In this case, `FooSingleton` is registered as a singleton, but it uses a factory to create new instances of `Bar` dynamically.

Registering the Factory

To use this approach, you need to register the factory in the IoC container. Here's how you might implement and register a simple factory:

csharp
public interface IFactory
{
    T Create();
}

public class BarFactory : IFactory
{
    public IBar Create()
    {
        return new Bar();
    }
}

// Register the factory
Mvx.IoCProvider.RegisterType, BarFactory>();

Dynamic Resolution

Alternatively, you can remove constructor injection and use dynamic resolution directly within the singleton class:

csharp
public class FooSingleton : IFooSingleton
{
    public FooSingleton() { }

    public void DoFoo()
    {
        var bar = Mvx.IoCProvider.Resolve();
        bar.DoStuff();
    }
}

In this scenario, `FooSingleton` is a singleton, but it resolves a new instance of `Bar` dynamically each time `DoFoo` is called.

Conclusion

MvvmCross allows you to mix dynamic and singleton types by using constructor injection with factories or dynamic resolution. This flexibility helps manage dependencies effectively, ensuring that your application can use both singleton and dynamic instances as needed.