Can I override the default ViewModel construction sequence in MvvmCross

Overriding ViewModel Construction

MvvmCross uses an IoC container to instantiate ViewModels and inject dependencies. To override the default construction behavior, you can implement a custom `IMvxViewModelLocator`. This allows you to control how ViewModels are created and initialized.

Implementing a Custom `IMvxViewModelLocator`

You can override the `IMvxViewModelLocator` in your App object to customize the ViewModel creation process. Here's an example of how you might implement this:

csharp
public class CustomViewModelLocator : IMvxViewModelLocator
{
    public MvxViewModel CreateViewModel(Type viewModelType, object parameter)
    {
        // Custom logic for creating the ViewModel
        if (viewModelType == typeof(MyCustomViewModel))
        {
            // Implement custom creation logic here
            return new MyCustomViewModel(parameter);
        }
        else
        {
            // Default creation logic
            return Mvx.IoCProvider.IoCConstruct(viewModelType) as MvxViewModel;
        }
    }
}

Then, in your App class, you need to set this custom locator:

csharp
public class App : MvxApplication
{
    public override void Initialize()
    {
        base.Initialize();

        // Set the custom ViewModel locator
        Mvx.RegisterSingleton(new CustomViewModelLocator());
    }
}

Overriding ViewModel Initialization

If you want to customize the initialization of a ViewModel (e.g., the `Init` method), you can do so by overriding the `Init` method in your ViewModel. This method is used to initialize the ViewModel with navigation parameters.

csharp
public class MyViewModel : MvxViewModel
{
    protected override Task Init(MyParameter parameter)
    {
        // Custom initialization logic here
        return base.Init(parameter);
    }
}

Customizing the Lifecycle

MvvmCross provides lifecycle methods like `ViewCreated`, `ViewAppearing`, etc., which you can override in your ViewModel to handle specific view-related events. These methods are called by the corresponding platform-specific views (e.g., `MvxViewController`, `MvxFragment`, `MvxActivity`).

csharp
public class MyViewModel : MvxViewModel
{
    public override void ViewAppearing()
    {
        // Custom logic when the view is appearing
        base.ViewAppearing();
    }

    public override void ViewDisappeared()
    {
        // Custom logic when the view has disappeared
        base.ViewDisappeared();
    }
}

Conclusion

MvvmCross provides a flexible framework for managing ViewModel construction and lifecycle. By implementing a custom `IMvxViewModelLocator` and overriding lifecycle methods, you can tailor the ViewModel creation and initialization process to fit your application's needs. This allows for more control over how ViewModels are instantiated and interact with their corresponding views.