question

Hello,
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I need to change one of my tabs' content depending on the condition of the user logged in or just a guest

Sure, you could make IMarkupExtension for ShellContent, and give current IMarkupExtension a bool property, when it is guest model return guest page.

 public class OnGuest : BindableObject, IMarkupExtension<ContentPage>
 {
     public readonly static BindableProperty IsGuestProperty = BindableProperty.Create(nameof(IsGuest), typeof(bool), typeof(OnGuest), null);
     public bool IsGuest
     {
         get { return (bool)GetValue(IsGuestProperty); }
         set { SetValue(IsGuestProperty, value); }
     }
    
    
     object IMarkupExtension.ProvideValue(IServiceProvider serviceProvider)
     {
         return (this as IMarkupExtension<Binding>).ProvideValue(serviceProvider);
     }
    
    
     public ContentPage ProvideValue(IServiceProvider serviceProvider)
     {
         if (IsGuest)
         {
             return new GuestPage();
         }
         else
         {
             return new UserPage();
         }         
     }
 }

Xaml Code

 <Tab Title="About" Icon="icon_about.png">
     <ShellContent>
         <local:OnGuest IsGuest="True"/>
     </ShellContent>
 </Tab>

For more info please refer to Creating XAML Markup Extensions.

Thank you.

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