How does MvvmCross manage dependencies and injections

Inversion of Control (IoC) and Dependency Injection (DI)

MvvmCross uses both the Service Locator pattern and Inversion of Control to manage dependencies. The IoC container allows you to register interfaces and their implementations, and then resolve these implementations as needed. Dependency Injection is a technique where components are given their dependencies rather than creating them internally. This decouples components from specific implementations, making the system more flexible and easier to test.

Registering Dependencies

In MvvmCross, you can register dependencies using various methods, such as `Mvx.RegisterType`, `Mvx.RegisterSingleton`, and `Mvx.ConstructAndRegisterSingleton`. These methods allow you to specify the lifetime of the registered objects, such as singleton or dynamic instances. For example:

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

Resolving Dependencies

Once dependencies are registered, you can resolve them using the `Mvx.Resolve` method. This method retrieves the registered implementation for a given interface. For instance:

csharp
var sqlFactory = Mvx.Resolve();

Constructor Injection

MvvmCross supports constructor injection, which allows objects to be created with their dependencies automatically resolved. When you create an object using `Mvx.IoCProvider.IocConstruct`, MvvmCross uses reflection to find the constructor, identify the required parameters, and resolve them using the IoC container. This process is recursive, meaning it can resolve nested dependencies. For example:

csharp
public class Bar
{
    public Bar(IFoo foo)
    {
        // Do stuff
    }
}

// Create Bar with IFoo resolved automatically
var bar = Mvx.IoCProvider.IocConstruct();

Recursive Resolution

The recursive nature of the resolution process means that if any resolved object requires additional dependencies, MvvmCross will automatically resolve those as well. This simplifies the creation of complex object graphs where multiple dependencies are nested.

App Class and Registration

In MvvmCross, the `App` class (which inherits from `MvxApplication`) is responsible for registering custom services and starting the application's ViewModels. It typically registers services as singletons and initializes the first ViewModel to display. The registration process can be automated using reflection to find classes ending with "Service" and register them as lazy singletons.

Lifecycle Management

MvvmCross manages the lifecycle of ViewModels and other components through its IoC container. ViewModels are instantiated with their dependencies injected, and their lifecycle is managed by the framework. This includes navigating between ViewModels and passing parameters, which are handled by the `Init` method in newer versions of MvvmCross.

Overall, MvvmCross's dependency management system provides a flexible and powerful way to decouple components and manage complex object relationships, making it easier to develop maintainable and testable cross-platform applications.