Object not set to an instance error on PopAsync()

Richy

Navigation to Tabbed Page

var tabbedPage = new TrialTabbedPage();
tabbedPage.BindingContext = new TrailTabViewModel(_originLatitud, _originLongitud, mile);
await Navigation.PushAsync(tabbedPage);

Tabbed Page

<TabbedPage xmlns="http://xamarin.com/schemas/2014/forms" xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml" xmlns:d="http://xamarin.com/schemas/2014/forms/design" xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" mc:Ignorable="d" x:Class="CureittApp.Views.TrialTabbedPage" xmlns:local="clr-namespace:CureittApp.Views"> <local:AdvancedTrailPage Title="List" BindingContext="{Binding TrailViewTab}"/> <local:TrailMapViewPage Title="Map" BindingContext="{Binding TrailViewTab}"/> </TabbedPage>~~~~

TrailTabViewModel

public class TrailTabViewModel
{
public AdvancedTrailModel TrailViewTab { get; set; }
public TrailTabViewModel(double latitude, double longitude, double mile)
{
TrailViewTab = new AdvancedTrailModel(latitude, longitude, mile, Navigation);
}
}

AdvancedTrailModel

await Navigation.PopAsync();

LandLu

Where did you call Navigation.PopAsync();?
We usually set the Tabbed Page as the root main page and won't use a navigation page wrap the tabbed page.
You can try to use Navigation.PushModalAsync(Page page) to present a tabbed page and use Navigation.PopModalAsync() to dismiss.
If you do want to use the navigation stack architecture try to post the sample here to help us reproduce the issue.

Richy

> @LandLu said:
> Where did you call Navigation.PopAsync();?
> We usually set the Tabbed Page as the root main page and won't use a navigation page wrap the tabbed page.
> You can try to use Navigation.PushModalAsync(Page page) to present a tabbed page and use Navigation.PopModalAsync() to dismiss.
> If you do want to use the navigation stack architecture try to post the sample here to help us reproduce the issue.

I called the Tabbed Page inside a navigation page, from a cs file. That cs file binded to a viewmodel page. From viewmodel I tried to pop that tabbed page.

If I use PushModalAsync do I get the back button on navigation bar?

LandLu

I called the Tabbed Page inside a navigation page, from a cs file. That cs file binded to a viewmodel page. From viewmodel I tried to pop that tabbed page.

You need to share your sample to help us understand this logic.

If I use PushModalAsync do I get the back button on navigation bar?

No. But you should create the navigation pages for each item in the tabbed page like:

So that each item could have its own navigation bar.

Richy

@LandLu said:

I called the Tabbed Page inside a navigation page, from a cs file. That cs file binded to a viewmodel page. From viewmodel I tried to pop that tabbed page.

You need to share your sample to help us understand this logic.

If I use PushModalAsync do I get the back button on navigation bar?

No. But you should create the navigation pages for each item in the tabbed page like:

So that each item could have its own navigation bar.

I already shared my code above

in my App.cs

MainPage = new MainPage();

inside MainPage (which is a MasterDetail Page)

Detail = new NavigationPage((Page)Activator.CreateInstance(item.TargetType));

in Default Detail Page(A button click navigates to following Page)

await Navigation.PushAsync(new MapSearchPage());

inside MapSearchPage(A button click navigates to a Tabbed Page)

var tabbedPage = new TrialTabbedPage();
tabbedPage.BindingContext = new TrailTabViewModel(_originLatitud, _originLongitud, mile);
await Navigation.PushAsync(tabbedPage);
…………… then follows rest of above code> @Richy said:

Navigation to Tabbed Page

var tabbedPage = new TrialTabbedPage();
tabbedPage.BindingContext = new TrailTabViewModel(_originLatitud, _originLongitud, mile);
await Navigation.PushAsync(tabbedPage);

Tabbed Page

<TabbedPage xmlns="http://xamarin.com/schemas/2014/forms" xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml" xmlns:d="http://xamarin.com/schemas/2014/forms/design" xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" mc:Ignorable="d" x:Class="CureittApp.Views.TrialTabbedPage" xmlns:local="clr-namespace:CureittApp.Views"> <local:AdvancedTrailPage Title="List" BindingContext="{Binding TrailViewTab}"/> <local:TrailMapViewPage Title="Map" BindingContext="{Binding TrailViewTab}"/> </TabbedPage>~~~~

TrailTabViewModel

public class TrailTabViewModel
{
public AdvancedTrailModel TrailViewTab { get; set; }
public TrailTabViewModel(double latitude, double longitude, double mile)
{
TrailViewTab = new AdvancedTrailModel(latitude, longitude, mile, Navigation);
}
}

AdvancedTrailModel

await Navigation.PopAsync();

LandLu

We can't use the code to reproduce your issue. You need to share an entire small sample so that I can run it to see the error you are facing.