MAUI Programmatically set Start/Root page

Question

MAUI Programmatically set Start/Root page

Dino 65

Hi everybody.
.net 7, VS 2022 latest, default maui application, mvvm toolkit, an half cup of coffee remaining.
I am porting, as a POC, an Android Application to MAUI.
I can successufully parse the deep link, and extract 'appmode' variable, storing it in a global variable. Url is a kind of myapp://.... &appmode=A&...

In the Android code, if appmode is A or B I inflate the correct Fragment and works flawlessy.

In MAUI I can in the App.cs constructor switch and set MainPage

  switch (Globals.AppMode)
        {
            case AppModeEnum.A:
                MainPage = new NavigationPage(new APage());
                break;

.... however this happens Before I parse querystring/deeplink in Platform/Android/MainActivity/OnCreate, so Globals.Appmode is not correctly set... yet.
Playing with AppShell (and using a different approach), for unknown reason, I loose the navigation and my pop/push async are ignored. I know I have to write the code, to explain but I will keep this post shorter.

Navigation is done with Mvvm (coomunity toolkit) messaging because of my experience in WPF, so the (root) View (PageA or PageB) registers and captures the message and navigate to correct View, populating the BindingContext received from NavigateToMessage parameter.

In PageA.cs code behind

 WeakReferenceMessenger.Default.Register<NavigateToMessage>(this, async (s, e) =>
 {
            DocumentPage d = new();
            d.BindingContext = e.ViewModel;
            await Navigation.PushAsync(d);
  });

So, sorry for the long description, is there a way to set the start/root page in my app, after deeplink is processed, and preserve the navigation functions?
Just for be complete, if app starts in mode A it has own Pages ad views and never "switch" in mode B, or viceversa. if PageA is root it will be for all app lifecycle.

Many thanks

Alessandro Caliaro 3,436 Reputation points

2023-03-15T08:33:38.0633333+00:00

can you post the activity?
Alessandro Caliaro 3,436 Reputation points

2023-03-15T09:14:53.93+00:00

it seems correct, you should have your data before the root page start, isn't it?

Dino 65

Here it is.

[Activity(Theme = "@style/Maui.SplashTheme", MainLauncher = true, ConfigurationChanges = ConfigChanges.ScreenSize | ConfigChanges.Orientation | ConfigChanges.UiMode | ConfigChanges.ScreenLayout | ConfigChanges.SmallestScreenSize | ConfigChanges.Density)]
[IntentFilter(new[] { Android.Content.Intent.ActionView },
                       AutoVerify = true,
                       Categories = new[]
                       {
                            Android.Content.Intent.CategoryDefault,
                            Android.Content.Intent.CategoryBrowsable
                       },
                       DataScheme = "myapp")]
public class MainActivity : MauiAppCompatActivity
{
    protected override void OnCreate(Bundle savedInstanceState)
    {
        Globals.ParseQueryString(Intent.Data?.Host, Intent.Data?.Query);
        base.OnCreate(savedInstanceState);
    }
}

Globals.ParseQueryString is a method for estract the querystring data and store them in global parameters.

Bye.

Dino 65 Reputation points

2023-03-15T10:36:16.6033333+00:00

No Alessandro,

the switch statment is inside the App.cs constructor; it is executed before the code in OnCreate of MainActivity. Breakpoint verified :-)

Alessandro Caliaro 3,436 Reputation points

2023-03-15T08:33:38.0633333+00:00

can you post the activity?
Alessandro Caliaro 3,436 Reputation points

2023-03-15T09:14:53.93+00:00

it seems correct, you should have your data before the root page start, isn't it?
Dino 65 Reputation points

2023-03-15T10:33:45.3066667+00:00

Here it is.

[Activity(Theme = "@style/Maui.SplashTheme", MainLauncher = true, ConfigurationChanges = ConfigChanges.ScreenSize | ConfigChanges.Orientation | ConfigChanges.UiMode | ConfigChanges.ScreenLayout | ConfigChanges.SmallestScreenSize | ConfigChanges.Density)] [IntentFilter(new[] { Android.Content.Intent.ActionView }, AutoVerify = true, Categories = new[] { Android.Content.Intent.CategoryDefault, Android.Content.Intent.CategoryBrowsable }, DataScheme = "myapp")] public class MainActivity : MauiAppCompatActivity { protected override void OnCreate(Bundle savedInstanceState) { Globals.ParseQueryString(Intent.Data?.Host, Intent.Data?.Query); base.OnCreate(savedInstanceState); } }

Globals.ParseQueryString is a method for estract the querystring data and store them in global parameters.

Bye.
Dino 65 Reputation points

2023-03-15T10:36:16.6033333+00:00

No Alessandro,

the switch statment is inside the App.cs constructor; it is executed before the code in OnCreate of MainActivity. Breakpoint verified :-)

Answer 1

Alessandro Caliaro 3,436

Yes,

[0:] MauiApp: MauiApp

[0:] App: App

[0:] AppShell: AppShell

[0:] MainActivity: OnCreate

this seems to be the execution flow.

Maybe you can move the switch inside the MainActivity?

Like this:

    protected override void OnCreate(Bundle savedInstanceState)
    {

        App.Current.MainPage = new AppShell();

        base.OnCreate(savedInstanceState);

    }

Dino 65

Alessandro MainActivity is called for last, as you wrote. And inside it I set AppMode variable...
Therefore the switch code (in App.cs constructor) is executed before OnCreate, this leads to:
In app.cs set the start Page based on AppMode default (wrong) value
Page shown is wrong (default is an ErrorPage, because AppModeEnum is set to Error in default)
... Executing OnCreate
AppMode becomes the correct value (say A - mode)
At this point the AppMode variable is set right, but is no more consumed...

public partial class App : Application
{
	public App()
	{
		InitializeComponent();
       // When this code is executed OnCreate is not yet called, so Globals.AppMode is not correctly set (yet)
        switch (Globals.AppMode)
        {
            case AppModeEnum.A:
                MainPage = new NavigationPage(new APage());
                break;
            case AppModeEnum.B:
                MainPage = new NavigationPage(new BPage());
                break;
            default:
            case AppModeEnum.Error:
                MainPage = new NavigationPage(new ErrorPage());
                break;
        }

    }
    
}

Alessandro Caliaro 3,436 Reputation points

2023-03-15T13:46:55.6566667+00:00
my suggestion is to move the switch to MainActivity, after the

base.OnCreate(savedInstanceState);
Dino 65 Reputation points

2023-03-15T14:27:17.9333333+00:00

Thanks Alessando,

But, after the switch, how i can set MainPage inside Android code of OnCreate method?

MainPage is not visible there...
Alessandro Caliaro 3,436 Reputation points

2023-03-15T14:50:51.28+00:00

edited the answer, take a look, for me it works

Dino 65

Alessandro, first I have to thank you... I hadn't read your answers with required attention.
Second, I thought it was not poossible to set the mainpage in Activity.
Now, with this code:

 protected override void OnCreate(Bundle savedInstanceState)
    {
        Globals.ParseQueryString(Intent.Data?.Host, Intent.Data?.Query);
        base.OnCreate(savedInstanceState);
        switch (Globals.AppMode)
        {
            case AppModeEnum.A:
                App.Current.MainPage = new NavigationPage(new APage());
                break;
            case AppModeEnum.B:
                App.Current.MainPage = new NavigationPage(new BPage());
                break;
            default:
            case AppModeEnum.Error:
                App.Current.MainPage = new NavigationPage(new ErrorPage());
                break;
        }
    }

all works ok. Navigation too.
Many thanks!

MAUI Programmatically set Start/Root page

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