Modal navigation back not working

[sthewissen]

Using 3.0.1, I have the following navigation pattern:

• My root is a TabbedPage, within the first tab sits a NavigationPage with a Page.
• From that Page I open a new Modal which is also a NavigationPage with Page.
• Pushing a new Page from that modally displayed Page and subsequently calling Back does nothing.

As far as I can tell, the system crashes on this line:

TinyMvvm/src/TinyMvvm.Forms/NavigationHelper/FormsNavigationHelper.cs

Line 340 in 07e4e09

var prevPage = Application.Current.MainPage.Navigation.NavigationStack[0];

With a:

Index was out of range. Must be non-negative and less than the size of the collection.
Parameter name: index

Because we're in a Modal popup with its own NavigationStack I would expect the first thing Back does to be to pop the newly pushed page on the Modal navigation stack. If there is nothing left to go Back to on that stack, I assume the result should be to pop the entire modal.

Changing that specific line to the following at the very least fixes the back navigation in my specific case, but I don't quite oversee the consequences this has for the rest yet. Hoping you have a bit more insight into that :)

var prevPage = Application.Current.MainPage.Navigation.ModalStack[0];

[dhindrik]

Have you tried the latest preview? There was a fix in a PR about modals. If that does not fix the problem I can investigate it further.

Thank you for creating the issue.

[sthewissen]

Still occurring on 4.0.1-pre4. If you want to check out a sample;

https://github.com/sthewissen/MVP/tree/updating-the-lot

Go to create a contribution and pick a contribution type from the list. It should pop the page back after picking.

[dhindrik]

It feels like something has changed with navigation in Xamarin.Forms since I wrote that code because it behaves very strangely. But I will investigate more how to fix it.

[BoobalanK]

Hey @dhindrik , I was having a problem in BackAsync. The ReturningParameter is null.

After i debugged the Sample Shell app from Samples Folder. I can see the 0 index in the NavigationStack is null. This is the reason the ReturningParameter never gets it value.

Hope this shed some light

[dhindrik]

@BoobalanK are you using Shell or not?

[BoobalanK]

Yes @dhindrik Using Shell. i tested the shell sample only from this location https://github.com/TinyStuff/TinyMvvm/tree/4.0.1-pre4/src/Samples

[dhindrik]

Are you using ShellViewBase?

[BoobalanK]

Yes @dhindrik

[vendhanparthy]

Hi @dhindrik, do you have any update for the ReturningParameter is null in BackAsync.