How do I resolve types explicitly in MvvmCross

Understanding the IoC Container

MvvmCross uses a simple IoC container that supports various registration patterns, such as singleton, dynamic, and lazy singleton registrations. The container is accessed through the `Mvx.IoCProvider` singleton instance, which acts as a central point for both registering and resolving interfaces and their implementations[7].

Registering Types

Before resolving a type, you need to register it in the IoC container. Registration can be done in several ways:

1. Singleton Registration: This registers a type as a singleton, meaning only one instance of the type will be created and reused throughout the application.

csharp
   Mvx.RegisterType();
   Mvx.RegisterSingleton();
   

2. Dynamic Registration: This allows for creating a new instance each time the type is resolved.

csharp
   Mvx.RegisterType();
   

3. Lazy Singleton Registration: This is similar to a singleton but the instance is created only when it is first requested.

csharp
   Mvx.RegisterType().AsLazySingleton();
   

Resolving Types

Once a type is registered, you can resolve it using the `Mvx.Resolve` method. This method returns an instance of the registered type.

csharp
ISQLiteConnectionFactory sqlFactory = Mvx.Resolve();

Constructor Injection

MvvmCross also supports constructor injection, which allows you to automatically resolve dependencies during object creation. This means you don't need to explicitly call `Mvx.Resolve` for dependencies if they are part of a constructor.

csharp
public class DataAccessLayerService
{
    private readonly ISQLiteConnectionFactory _sqlFactory;

    public DataAccessLayerService(ISQLiteConnectionFactory sqlFactory)
    {
        _sqlFactory = sqlFactory;
    }
}

When you create an instance of `DataAccessLayerService`, MvvmCross will automatically resolve the `ISQLiteConnectionFactory` instance if it is registered in the IoC container.

Common Issues

- Failed to Resolve Type: If you encounter an error saying that MvvmCross failed to resolve a type, ensure that the type is properly registered in the IoC container before attempting to resolve it[4].

- ViewModel Resolution: When working with ViewModels, MvvmCross automatically wires up the ViewModel for you. Instead of using `Mvx.Resolve` to get a ViewModel instance, you should access it through the `ViewModel` property available in the View[4].

Conclusion

Resolving types explicitly in MvvmCross is straightforward using the `Mvx.Resolve` method. However, leveraging constructor injection can simplify your code and make it more maintainable by letting MvvmCross handle dependency resolution automatically.