Question

I have a little problem, which I can’t solve..

Well, I built a BaseActivity.cs Class:

public class BaseActivity<T> : MvxBindingTabActivityView<T> where T : class, IMvxViewModel
{
    protected override void OnViewModelSet()
    { }

    public override bool OnCreateOptionsMenu(IMenu menu)
    {
        // GroupId, ItemId, OrderId
        menu.Add(0, 0, 0, "Einstellungen").SetIcon(Android.Resource.Drawable.IcMenuManage);
        menu.Add(0, 1, 1, "Info").SetIcon(Android.Resource.Drawable.IcMenuInfoDetails);
        return true;
    }

    public override bool OnOptionsItemSelected(IMenuItem item)
    {
        var id = item.ItemId + 1; // (Id is zero-based :)
        if (id == 1) // First Item
        {
            StartActivity(typeof(SettingsShowActivity));
        }
        else if (id == 2) // Second Item
        {
            Android.App.AlertDialog.Builder builder = new AlertDialog.Builder(this);
            AlertDialog ad = builder.Create();
            ad.SetTitle("Information");
            ad.SetIcon(Android.Resource.Drawable.IcDialogAlert);
            ad.SetMessage("Version: 0.1");
            ad.SetButton("OK", (s, e) => { Console.WriteLine("OK Button clicked, alert dismissed"); });
            ad.Show();
        }
        return true;
    }
}

The goal of this class is, that I can put things in that I will use in every other Activity, just like here, the OptionsMenu, which is more or less on all Activities..

Then my other two Activities which are inheriting from BaseActivity.cs:

the MainScreenActivity.cs:

[Activity]
public class MainScreenActivity : BaseActivity<MainScreenViewModel>
{
    protected override void OnViewModelSet()
    {
        SetContentView(Resource.Layout.MainScreenLayout);

        TabHost.TabSpec spec;    
        Intent intent;

        intent = base.CreateIntentFor<AddressesSearchViewModel>();
        intent.AddFlags(ActivityFlags.NewTask);

        spec = TabHost.NewTabSpec("adressen");
        spec.SetIndicator("Adressen");
        spec.SetContent(intent);
        TabHost.AddTab(spec);


        intent = base.CreateIntentFor<ContactsSearchViewModel>();
        intent.AddFlags(ActivityFlags.NewTask);

        spec = TabHost.NewTabSpec("kontaktpersonen");
        spec.SetIndicator("Kontaktpersonen");
        spec.SetContent(intent);
        TabHost.AddTab(spec);
    }

    protected override void OnCreate(Bundle bundle)
    {
        base.OnCreate(bundle);
    }
}

and the LoginActivity.cs:

[Activity]
public class LoginActivity : BaseActivity<LoginViewModel>
{
    protected override void OnResume()
    {
        base.OnResume();
        App.IsLoggedIn = false;
    }

    protected override void OnCreate(Bundle bundle)
    {
        base.OnCreate(bundle);
    }

    protected override void OnViewModelSet()
    {
        SetContentView(Resource.Layout.Login);
        //App.MessageHub.Subscribe<ErrorMessage>((m) => { ErrorMessageAlert(m.Message, m.Title); });
    }
}

Its compiling fine, but the app crashes when I start it, and thats the errormessage I get: Your content must have a TabHost whose id attribute is 'android.R.id.tabhost‘ . I suggest, that it is because I “needed” to implement the abstract interface into the BaseActivity.cs :

protected override void OnViewModelSet()
{ }

So maybe he walks into the ‘false’ OnViewModelSet(), (In the empty one instead of the one which is building the Tabhost).. but I’m actually not sure.. btw this comes from: MvxBindingTabActivityView..

Hmm any help would be appreciated

Answer 1

I think this is a quite simple problem…

MvxBindingTabActivityView inherits from TabActivity (see source) and it’s this class that requires the content – Your content must have a TabHost whose id attribute is 'android.R.id.tabhost'

If you don’t want to use Tabs, then just inherit from MvxBindingActivityView instead – this is what the conference sample does – https://github.com/slodge/MvvmCross/blob/vnext/Sample%20-%20CirriousConference/Cirrious.Conference.UI.Droid/Views/BaseView.cs

If one of your activities needs to do tabs, but the other doesn’t then they need to inherit using different inheritance trees. If you want to share code between the two base classes, then the best way to do this in C# seems to be using extension methods – e.g. see BaseViewExtensionMethods.cs shared between BaseView.cs, BaseTabbedView.cs and BaseMapView.cs in the conference sample.