How does MvvmCross support ViewModel to ViewModel navigation

Overview of MvvmCross Navigation

MvvmCross uses the `IMvxNavigationService` interface to manage navigation between ViewModels. When a ViewModel requests navigation to another ViewModel, MvvmCross automatically locates the corresponding View for the target ViewModel, creates an instance of that View, and sets the target ViewModel as its `DataContext`[1][3].

Key Components and Methods

- `IMvxNavigationService`: This is the core interface for navigating between ViewModels. It provides methods like `Navigate()` and `Navigate(TParameter parameter)` to navigate to different ViewModels with or without parameters[3][5].

- `ShowViewModel()`: This method is used to navigate to a specific ViewModel. It is similar to `Navigate()` but is more commonly used in older versions of MvvmCross[3].

- `Close(this)`: This method is used to close the current ViewModel and return to the previous one in the navigation stack[3].

Navigation with Parameters

MvvmCross allows passing complex parameters between ViewModels using the `Navigate(TParameter parameter)` method. The receiving ViewModel must implement `IMvxViewModel` or inherit from `MvxViewModel` to handle these parameters. Parameters are serialized using JSON, so you need to have the MvvmCross Json plugin installed or register your own `IMvxJsonConverter` for custom types[3].

Lifecycle Methods

MvvmCross provides lifecycle methods for ViewModels, such as `ViewAppearing()`, `ViewAppeared()`, `ViewDisappearing()`, and `ViewDisappeared()`, which are called in response to View lifecycle events. These methods can be used to perform actions when the View is about to appear or disappear[7][8].

Customization

MvvmCross allows customization of the navigation process. For example, you can override the default ViewModel location and construction by implementing a custom `IMvxViewModelLocator` in your App object[10].

Example of Navigation

Here's an example of how to navigate from one ViewModel to another using MvvmCross:

csharp
public class FirstViewModel : MvxViewModel
{
    private readonly IMvxNavigationService _navigationService;

    public FirstViewModel(IMvxNavigationService navigationService)
    {
        _navigationService = navigationService;
    }

    public IMvxAsyncCommand NavigateCommand => new MvxAsyncCommand(() => _navigationService.Navigate());
}

In this example, when the `NavigateCommand` is executed, it navigates to `SecondViewModel` using the `IMvxNavigationService`. MvvmCross will automatically locate the corresponding View for `SecondViewModel`, create it, and set `SecondViewModel` as its `DataContext`[1].