MVVMCross programmatically change start ViewModel

问题:

The portable class library defines the start view model. This scenario generally sounds great but I was considering this. You have written a iOS universal application or Android that needs to change its start screen / view model. If application is a phone, the default view model is login but if it is tablet, you want a different view model as the start. Is there an override or a way to take control of this?

回答1:

See the Wiki section - https://github.com/MvvmCross/MvvmCross/wiki/Customising-using-App-and-Setup#custom-imvxappstart - this has an example of programmatic switching:

---

If more advanced startup logic is needed, then a custom app start can be used - e.g.

public class CustomAppStart
    : MvxNavigatingObject
    , IMvxAppStart
{
    public void Start(object hint = null)
    {
        var auth = Mvx.Resolve<IAuth>();
        if (auth.Check())
        {
            ShowViewModel<HomeViewModel>();
        }
        else
        {
            ShowViewModel<LoginViewModel>();
        }
    }
}

This can then be registered in App using:

RegisterAppStart(new CustomAppStart());

回答2:

In your App class you could register an AppStart that is a splash screen:

RegisterAppStart<SplashScreenViewModel>() 

In that splash screen you could receive a service that verifies if it's a tablet or a phone. You would need to create a plugin to make this verification. (There are other stackoverflow questions showing how to verify this / How to detect device is Android phone or Android tablet? )

public SplashScreenViewModel(ITabletVerificationService tabletVerificationService)

Then you would simply change screen according to this service

if(tabletVerificationService.IsTablet())
{
   ShowViewModel<TabletViewModel>
}
else
{
  ShowViewModel<LoginViewModel>
}

Hope it helps =)

回答3:

Here's my implementation of this scenario, if it could help:

PCL:

public enum PlateformType
{
    Android,
    iPhone,
    WindowsPhone,
    WindowsStore
}

public interface IPlateformInfos
{
    PlateformType GetPlateformType();
}

public class CustomAppStart
: MvxNavigatingObject
, IMvxAppStart
{
    public void Start(object hint = null)
    {
        var plateformInfos = Mvx.Resolve<IPlateformInfos>();
        var plateformType = plateformInfos.GetPlateformType();
        switch (plateformType)
        {
            default:
                ShowViewModel<MenuViewModel>();
                break;
            case PlateformType.WindowsPhone:
            case PlateformType.WindowsStore:
                ShowViewModel<FirstViewModel>();
                break;
        }
    }
}

PCL App.cs:

RegisterAppStart(new CustomAppStart());

UI (ex: WindowsPhone):

public class PlateformInfos : IPlateformInfos
{
    public PlateformType GetPlateformType()
    {
        return PlateformType.WindowsPhone;
    }
}

UI Setup.cs:

protected override void InitializeFirstChance()
{
    Mvx.RegisterSingleton<IPlateformInfos>(new PlateformInfos());
    base.InitializeFirstChance();
}

Pretty simple way.