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MvvmCross uses ViewModel first navigation. Meaning that we navigate from ViewModel to ViewModel and not from View to View. In MvvmCross the ViewModel will lookup its corresponding View. By doing so we don’t have to write platform specific navigation and we can manage everything from within our core.

The navigation enables you to inject it into your ViewModels, which makes it more testable, and gives you the ability to implement your own navigation! Other main features are that it is fully async and type safe. For more details see #1634

The following Api is available to use:

public interface IMvxNavigationService
{
    event BeforeNavigateEventHandler BeforeNavigate;
    event AfterNavigateEventHandler AfterNavigate;
    event BeforeCloseEventHandler BeforeClose;
    event AfterCloseEventHandler AfterClose;
    event BeforeChangePresentationEventHandler BeforeChangePresentation;
    event AfterChangePresentationEventHandler AfterChangePresentation;

    Task Navigate(IMvxViewModel viewModel, IMvxBundle presentationBundle = null);
    Task Navigate<TParameter>(IMvxViewModel<TParameter> viewModel, TParameter param, IMvxBundle presentationBundle = null);
    Task<TResult> Navigate<TResult>(IMvxViewModelResult<TResult> viewModel, IMvxBundle presentationBundle = null, CancellationToken cancellationToken = default(CancellationToken));
    Task<TResult> Navigate<TParameter, TResult>(IMvxViewModel<TParameter, TResult> viewModel, TParameter param, IMvxBundle presentationBundle = null, CancellationToken cancellationToken = Running Fuzex Red US Coral True 6 ASICS Women's Flash Shoe Oat Red M default(CancellationToken));

    Task Navigate(Type viewModelType, IMvxBundle presentationBundle = null);
    Task Navigate<TParameter>(Type viewModelType, TParameter param, IMvxBundle presentationBundle = null);
    Task<TResult> Navigate<TResult>(Type viewModelType, IMvxBundle presentationBundle = null, CancellationToken cancellationToken = default(CancellationToken));
    Task<TResult> Navigate<TParameter, TResult>(Type viewModelType, TParameter param, IMvxBundle presentationBundle = null, CancellationToken cancellationToken = default(CancellationToken));

    Task Navigate(string path, IMvxBundle presentationBundle = null);
    Task Navigate<TParameter>(Oat Coral M True Shoe 6 ASICS Fuzex Flash Red Women's Running US Red string path, TParameter param, IMvxBundle presentationBundle = null);
    Task<TResult> Navigate<TResult>(string path, IMvxBundle presentationBundle = null, CancellationToken cancellationToken = default(CancellationToken));
    Task<TResult> Navigate<TParameter, TResult>(string path, TParameter param, IMvxBundle presentationBundle = null, CancellationToken cancellationToken = default(CancellationToken));

    Task Navigate<TViewModel>(IMvxBundle presentationBundle = null) where TViewModel : IMvxViewModel;
    Task Navigate<TViewModel, TParameter>(TParameter param, IMvxBundle presentationBundle = null) where TViewModel : IMvxViewModelWomen's Red Running Fuzex True Red Coral 6 M Oat Flash ASICS Shoe US <TParameter>;
    Task<TResult> Navigate<TViewModel, TResult>(IMvxBundle presentationBundle = null6 Women's Fuzex M Flash ASICS Shoe Red Coral Running US Oat Red True , CancellationToken cancellationToken = default(CancellationToken)) where TViewModel : IMvxViewModelResult<TResult>;
    Task<TResult> Navigate<TViewModel, TParameter, TResult>(TParameter param, IMvxBundle presentationBundle = null, CancellationToken cancellationToken = default(CancellationToken)) where TViewModel : IMvxViewModelShoe US 6 Flash Oat Fuzex Red M ASICS True Red Coral Women's Running <TParameter, TResult>;

    Task<bool> CanNavigate(string path);

    Task<bool> Close(IMvxViewModel viewModel);
    Task<bool> Close<TResult>(IMvxViewModelResult<TResult> viewModel, TResult result);

    Task<bool> ChangePresentation(MvxPresentationHint hint);
}

Some extension methods make it easier to use your already existing code:

public static class MvxNavigationExtensions
{
    public static Task<bool> Flash Oat Running Fuzex True 6 Red Shoe Women's US Red ASICS Coral M CanNavigate(this IMvxNavigationService navigationService, Uri path)

    public static Task Navigate(this IMvxNavigationService navigationService, Uri path, IMvxBundle presentationBundle = null)
    public static Task Navigate<TParameter>(this IMvxNavigationService navigationService, Uri path, TParameter param, IMvxBundle presentationBundle = null)
    public static Task Navigate<TResult>(this IMvxNavigationService navigationService, Uri path, IMvxBundle presentationBundle = null, CancellationToken cancellationToken = default(CancellationToken))
    public static Task Navigate<TParameter, TResult>(this IMvxNavigationService navigationService, Uri path, TParameter param, IMvxBundle presentationBundle = nullTrue ASICS Coral US Fuzex 6 Shoe Red Red Running Women's Flash M Oat , CancellationToken cancellationToken = 6 Red US Running Women's Coral ASICS Red Fuzex Shoe True M Flash Oat default(CancellationToken))
}

In your ViewModel this could look like:

public class MyViewModel : MvxViewModel
{
    private readonly IMvxNavigationService _navigationService;

    public MyViewModel(IMvxNavigationService navigationService)
    {
        _navigationService = navigationService;
    }
    
    public override void Prepare()
    {
        // first callback. Initialize parameter-agnostic stuff here
    }

    public async Task Initialize()
    {
        await base.Initialize();

        // do the heavy work here
    }

    public async Task SomeMethod()
    {
        await _navigationService.Navigate<NextViewModel, MyObject>(new MyObject());
    }
}

public class NextViewModel : MvxViewModel<MyObject>F821SN413AG UK Women Glitter Kenzo Sneakers Silver PqIt7Y
{
    private MyObject _myObject;

    public override void Prepare()
    {
        // first callback. Initialize parameter-agnostic stuff here
    }

    public override void Prepare(MyObject parameter)
    {
        // receive and store the parameter here
        _myObject = parameter;
    }
    
    public override async Task Initialize()
    {
        await base.Initialize();

        // do the heavy work here
    }
}

When you want to return a result to the place where you navigated from you can do:

public class MyViewModel : MvxViewModel
{
    private readonly IMvxNavigationService _navigationService;
    public MyViewModel(IMvxNavigationService navigation)
    {
        _navigationService = navigationService;
    }
    
    public override void Prepare()
    {
        // first callback. Initialize parameter-agnostic stuff here
    }

    public override async Task Initialize()
    {
        await base.Initialize();
        
        // do the heavy work here
    }

    public async Task SomeMethod()
    {
        var result = await _navigationService.Navigate<NextViewModel, MyObject, MyReturnObject>(new MyObject());
        //Do something with the result MyReturnObject that you get back
    }
}

public class NextViewModel : MvxViewModel<MyObject, MyReturnObject>
{
    private readonly IMvxNavigationService _navigationService;

    private MyObject _myObject;

    public MyViewModel(IMvxNavigationService navigation)
    {
        _navigationService = navigationService;
    }

    public override void Prepare()
    {
        // first callback. Initialize parameter-agnostic stuff here
    }
    
    public override void Prepare(MyObject parameter)
    {
        // receive and store the parameter here
        _myObject = parameter;
    }
    
    public override async Task Initialize()
    {
        //Do heavy work and data loading here
    }
    
    public async Task SomeMethodToClose()
    {
        await _navigationService.Close(this, new MyReturnObject());
    }
}

You can provide a CancellationToken to abort waiting for a Result. This will close the ViewModel and cancel the Task.

If you have a BaseViewModel you might not be able to inherit MvxViewModel or MvxViewModel because you already have the BaseViewModel as base class. In this case you can implement the following interface:

IMvxViewModel, IMvxViewModelResult or IMvxViewModel

To implement returning your own result add the following to your (Base)ViewModel:

public override TaskCompletionSource<object> CloseCompletionSource { get; set; }

public override void ViewDestroy(bool viewFinishing = true)
{
    if (viewFinishing && CloseCompletionSource != null && !CloseCompletionSource.TaskUS Coral Red Flash 6 Red Running ASICS True Women's Fuzex Oat M Shoe .IsCompleted && !CloseCompletionSource.Task.IsFaulted)
        CloseCompletionSource?.TrySetCanceled();

    base.ViewDestroy(viewFinishing);
}

To check if you are able to navigate to a certain ViewModel you can use the CanNavigate method.

if (Mvx.Resolve<IMvxNavigationService>().CanNavigate<NextViewModel>())
{
    //Do something
}

If you want to intercept ViewModel navigation changes you can hook into the events of the NavigationService.

Mvx.Resolve<IMvxNavigationService>().AfterClose += (object sender, NavigateEventArgs e) =>
 {
    //Do something with e.ViewModel
};

The events available are:

  • BeforeNavigate
  • AfterNavigate
  • BeforeClose
  • AfterClose
  • BeforeChangePresentation
  • AfterChangePresentation

You might be using Init() or Start() methods in your ViewModels when updating from MvvmCross 4.x. These are now deprecated because it was done using reflection and therefore not very safe. When MvxNavigationService is used, a typed method called Task Initialize() will be available for you to perform any async heavy operations.

Uri navigation

The Uri navigation of the NavigationService will build the navigation stack if required. This will also enable deeplinking and building up the navigationstack for it. Every ViewModel added to the stack can split up into multiple paths of it’s own backstack. This will enable all kinds of layout structures as Hamburger, Tab or Top navigation.

The NavigationService supports multiple URIs per ViewModel as well as “NavigationFacades” that return the right ViewModel + parameters depending on the URI.

The solution is composed of:

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  • Navigation Attribute (ViewModel/Facade, URI regex)
  • NavigationFacades are constructed via Mvx.IocConstruct to profit from dependency injection
  • NavigationService, registered as a singleton, uses IMvxViewDispatcher to show the viewmodels
  • Necessary additions to Android (Activity.OnNewIntent) + iOS (AppDelegate.OpenUrl) (look a the example project for more infos) You can also use this solution for triggering deeplink from outside the app:

Register a custom scheme (i.e. “foo”) in our app (look a the example project for me info) Push-Messages: Depending on the status of the app you can pass a uri as the Notification Parameter, so when the app starts you can deep link directly to the view you want.

Supply your routings as assembly attributes. We would recommend putting them in the same file as the referenced ViewModel.

[assembly: MvxNavigation(typeof(ViewModelA), @"mvx://test/\?id=(?[A-Z0-9]{32})$")] namespace *.ViewModels
{
    public class ViewModelA
        : MvxViewModel
    {
    	public void Init(string id) // you can use captured groups defined in the regex as parameters here
        {

        }
    }
}

Routing in a ViewModel.

public class MainViewModel : MvxViewModel
{
    private readonly IMvxNavigationService _navigationService;

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

    private IMvxAsyncCommand _showACommand;
    public IMvxAsyncCommand ShowACommand
    {
        get
        {
            return _showACommand ?? (_showACommand = new MvxAsyncCommand(async () =>
            {
                await _navigationService.Navigate("mvx://test/?id=" + Guid.NewGuid().ToString("N"));
            }));
        }
    }
}

Facades

Say you are building a task app and depending on the type of task you want to show a different view. This is where NavigationFacades come in handy (there is only so much regular expressions can do for you).

mvx://task/?id=00000000000000000000000000000000 <– this task is done, show read-only view (ViewModelA) mvx://task/?id=00000000000000000000000000000001 <– this task isn’t, go straight to edit view (ViewModelB)

[assembly: MvxRouting(typeof(SimpleNavigationFacade), @"mvx://task/\?id=(?[A-Z0-9]{32})$")] namespace *.NavigationFacades
{
	public class SimpleNavigationFacade
	    : IMvxNavigationFacade
	{
	    public Task<MvxViewModelRequest> BuildViewModelRequest(string url,
	        IDictionary<string, string> currentParameters, MvxRequestedByGown Papell Hunter Geometric Beaded Women's Adrianna IBqdI requestedBy)
	    {
	    	// you can load data from a database etc.
	    	// try not to do a lot of work here, as the user is waiting for the UI to do something ;)
	        var viewModelType = currentParameters["id"] == Guid.Empty.ToString("N")Chupeng Gown Evening Lace Long Formal Party Prom Size Plus Mint Sweetheart Ball Dress Black SFpHqwSr ? Shoe US ASICS Running Oat Women's M Red Red Fuzex 6 True Flash Coral typeof(ViewModelA) Fuzex US Running Coral ASICS Women's True Red Flash Red Shoe Oat 6 M : typeof(ViewModelB);

	        return Task.FromResult(new MvxViewModelRequest(viewModelType, new MvxBundle(), null, requestedBy));
	    }
	}
}

Upgrading from 4.x to 5.x

To make sure your navigation stays up-to-date change all your ShowViewModel<>() calls to the new navigation methods.

Example before:

private IMvxCommand _navigateCommand;
public IMvxCommand NavigateCommand
{
    get
    {
        _navigateCommand = _navigateCommand ?? new MvxCommand(() => ShowViewModel<TViewModel>());
        return _navigateCommand;
    }
}

After:

private IMvxAsyncCommand _navigateCommand;
public IMvxAsyncCommand NavigateCommand
{
    get
    {
        _navigateCommand = _navigateCommand ?? new MvxAsyncCommand(() => _navigationService.Navigate<TViewModel>());
        return _navigateCommand;
    }
}

Simple ViewModel navigation

To navigate from a ViewModel to another ViewModel you can use ShowViewModel command. The ShowViewModel command will take a Generic type which should represent the ViewModel that you want to navigate to.

ShowViewModel<TViewModel>();

If we want to for example navigate to the DetailViewModel we only have to call the command from within another ViewModel.

ShowViewModel<DetailViewModel>();

To move back to the previous ViewModel we can call Close(this); on the ViewModel that we want to close.

Every object can be passed to another ViewModel as a parameter. If its is desired to pass data along in the form of a more complex parameter it can be done like so:

ShowViewModel<TViewModel, TParameter>(new TParameter());

To be able to retrieve this the receiving class should implement the expected parameter on a class level and implement the correct init:

public class MyViewModel : MvxViewModel<TParameter>
{
    protected override Task Init(TParameter parameter)
    {
        // use the parameters here
    }
}

If you have a BaseViewModel you might not be able to inherit MvxViewModel because you already have the BaseViewModel as base class. In this case you can implement the following interface:

IMvxViewModel<TParameter>

MvvmCross uses JSON to serialize the object and to use complex parameters you should have the MvvmCross Json plugin installed or register your own IMvxJsonConverter.

As you write apps, you may frequently find that you want to parameterize a ViewModel navigation.

For example, you may encounter List-Detail situations - where:

  • The Master view shows a list of items.
  • When the user selects one of these, then the app will navigate to a Detail view
  • The Detail view will then shows that specific selected item.

To achieve this, the navigation from MasterViewModel to DetailViewModel will normally be achieved by:

  • we declare a class DetailParameters for the navigation:
public class DetailParameters
{
    public int Index {
        get;
        set;
    }
}
  • the MasterViewModel makes ShowViewModel a call like:

ShowViewModel(new DetailParameters() { Index = 2 });

  • the Red Women's True Flash M Coral ASICS Shoe 6 Fuzex Red US Oat Running DetailViewModel declares an Init method in order to receive this DetailParameters:
public void Init(DetailParameters parameters)
{
    // use the parameters here
}

Note that the DetailParameters class used here must be a ‘simple’ class used only for these navigations:

  • it must contain a parameterless constructor
  • it should contain only public properties with both get and set access
  • these properties should be only of types:
    • bool
    • Integral types: sbyte, short, int, long, byte, ushort, uint, ulong
    • Floating-point types: float, double
    • decimal
    • char
    • string
    • DateTime
    • Guid
    • Enumeration values

For simple navigations, declaring a formal Parameters object can feel like ‘overkill’ - like ‘hard work’.

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In these situations you can instead use anonymous classes and named method arguments.

For example, you can:

  • use a call to ShowViewModel like:

ShowViewModel(new { index = 2 });

  • in the Flash Shoe Red Running Coral ASICS Oat M True US 6 Red Fuzex Women's DetailViewModel declare an Init method in order to receive this index as:
public void Init(int index)
{
    // use the index here
}

Note that due to serialization requirements, the only available parameter types used within this technique are only:

  • bool
  • Integral types: sbyte, short, int, long, byte, ushort, uint, ulong
  • Floating-point types: float, double
  • decimal
  • char
  • string
  • DateTime
  • Guid
  • Enumeration values