TabbedPage crashes app on start up. Others don't - xaml

Question

I encountered this issue tonight and after hours of brainstorming I thought i'd ask. Please refer to the code below:
App.xaml.cs
MainPage = new NavigationPage(new MainPage());
// MainPage = new NavigationPage(new ActivitiesPage());
The above code does not run for some reason. I have done a test with the commented code below and everything functions just how it should. Does anyone know the reason for this? The code for both xaml classes (MainPage and ActivitiesPage) are below.
MainPage
<TabbedPage xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
x:Class="Instagram_App.View.MainPage"
xmlns:view="clr-namespace:Instagram_App.View;assembly=Instagram_App">
<view:ActivitiesPage Title="Activities" Icon="heart.png"/>
<view:ProfilePage Title="Profile" Icon="user.png"/>
</TabbedPage>
ActivitiesPage
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
x:Class="Instagram_App.View.ActivitiesPage">
<ContentPage.Content>
<ListView x:Name="listView" ItemSelected="ListView_OnItemSelected" HasUnevenRows="True">
<ListView.ItemTemplate>
<DataTemplate>
<ViewCell>
<StackLayout Orientation="Horizontal" HorizontalOptions="StartAndExpand">
<Image Source="{Binding ImageUrl}" />
<Label Text="{Binding Description}"/>
</StackLayout>
</ViewCell>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
</ContentPage.Content>
</ContentPage>
I have stepped through the code to see what happens and it seems that when the compiler gets to OnStart() it crashes. Please help and thanks!

Answer 1

A TabbedPage should be the root (MainPage) of your App, not contained within a NavigationPage. However, each tab within a TabbedPage can contain a NavigationPage
<TabbedPage xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
xmlns:local="clr-namespace:TabbedPageWithNavigationPage;assembly=TabbedPageWithNavigationPage"
x:Class="TabbedPageWithNavigationPage.MainPage">
<local:TodayPage />
<NavigationPage Title="Schedule" Icon="schedule.png">
<x:Arguments>
<local:SchedulePage />
</x:Arguments>
</NavigationPage>
</TabbedPage>

Answer 2

According to your code，
your MainPage should be setted as TabbedPage and Root of Your App.
So you could modify App.xaml.cs as follows:
MainPage = new MainPage();
If you want tab Contain NavigationPage to TabbedPage, you can use the Last responder's answer:
<TabbedPage xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
xmlns:local="clr-namespace:TabbedPageWithNavigationPage;assembly=TabbedPageWithNavigationPage"
x:Class="TabbedPageWithNavigationPage.MainPage">
<local:TodayPage />
<NavigationPage Title="Schedule" Icon="schedule.png">
<x:Arguments>
<local:SchedulePage />
</x:Arguments>
</NavigationPage>
And,if have Doubt，you can refer to the official documentation：
[TabbedPage use and demo][1]
[1]: https://learn.microsoft.com/en-us/xamarin/xamarin-forms/app-fundamentals/navigation/tabbed-page