Error passing parameters to mvvmcross viewmodels

Question

I found this example in the Bestseller exmaple

public ICommand ViewDetailCommand
{
    get { return new MvxRelayCommand(() => RequestNavigate<BookViewModel>(new { category= CategoryEncoded, book=ISBN })); }
}

public BookViewModel(string category = null, string book = null)
{
    category = category ?? string.Empty;
    book = book ?? string.Empty;

    AsyncFindBook(category, book);
 }

So I have tried doing

public IMvxCommand GetGpsCommand
{
    get
    {
        return new MvxRelayCommand<SetupViewModel>(type => RequestNavigate<GpsViewModel>(new {installedMeter = _installedMeter}));
    }
}

public GpsViewModel(InstalledMeter installedMeter = null)
{
    _installedMeter = installedMeter;

    Latitude = 0.0;
    Longitude = 0.0;
    ButtonStartReading = "Start";

    this.GetService<IGpsService>().CoordinatesFoundEvent += CoordinatesFound;
    //this.GetService<IGpsService>().StartReading();
}

But when I try this I just get

Cirrious.MvvmCross.Exceptions.MvxException: Failed to load ViewModel for type Core.ViewModels.InstallUnit.GpsViewModel from locator MvxDefaultVi…

score 2 · Accepted Answer · edited May 23 '17 at 12:32

Update: this answer is no longer up-to-date for MvvmCross

MvvmCross now supports ints, longs, enums, doubles and strings. Further, you can navigate by your own serializable types using the advice on: http://slodge.blogspot.co.uk/2013/01/navigating-between-viewmodels-by-more.html

Original answer:

This is an error that is often encountered.

MvvmCross navigation parameters must be strings

The reason for this is because the navigation itself needs to be serialized to a Xaml Url on WP7/8 and to an Intent on Android.

For more info, see:

Passing on variables from ViewModel to another View (MVVMCross)

and

Constructor in ViewModel

For more frequent navigation problems, check out the Navigation section on: http://slodge.blogspot.co.uk/p/mvvmcross-quicklist.html

If you believe more types should be supported then there is an open issue request - https://github.com/slodge/MvvmCross/issues/45

For small data-only objects, you can serialize them to text and pass them through this constructor mechanism. The only limits really are the size limits placed on Xaml Urls (these can get quite small).

However, for most cases, I would expect that viewModel-viewModel navigation will pass some kind of lookup key - using to a persistent-service. MvvmCross can help with the navigation, but it the app developer needs to understand the lifecycle of each app within its OS.

Would it be wise serialize the object I want to pass and then send it? — Mech0z, Nov 06 '12 at 07:43
Basically - yes, you can, but that's not the case for most apps I've written. Answer updated with further comment. Also see http://www.gregshackles.com/2012/11/returning-results-from-view-models-in-mvvmcross/ — Stuart, Nov 06 '12 at 09:24
Is there some place I can put object instance shared between several different ViewModels in MvvmCross? Or would I have to parse it to each instance using IoC, don't want to hit those size limitations. — Mech0z, Nov 06 '12 at 09:28
Comments too hard to discuss new questions in. Try it and see? Or put a longer new question together? — Stuart, Nov 06 '12 at 09:39

Error passing parameters to mvvmcross viewmodels

1 Answers1

Linked