[Bug] Flyout page INavigationAware events incorect triggering

[amaneshi]

Description

Thank you for great framework, very like it! Found small bug in Flyout page events handling, but I really need to work right (made some ugly workaround).

So I have some simple root navigation page, e.g. /NavigationPage/HomePage. Then I navigate to Flyout page with some setting pages with path /MainPage/NavigationPage/SomeDetailPage ("MainPage" is Flyout page). Till now everything work as expected. After that when I navigate to other Flyout detail pages (with NavigationPage/OtherDetailPage) I use INavigationAware method OnNavigatedFrom inside detail page to cleanup state changes and event trigerred.

But then I try to return to HomePage with /NavigationPage/HomePage and this time method OnNavigatedFrom on last active detail page was not triggered. I made some additional checks - can add that same event, OnNavigatedFrom, in parent VM (for Flyout page itself) still triggered as expected, but not in detail page.

Steps to Reproduce

1. Open App - Home page is root page
2. Press button to open Flyout page with 2 detail pages
3. On Flyout page switch between detail page to see in debug console 2 messages from OnNavigatedFrom in detail page and Flyout page itself
4. From side menu press button to return to home page and in debug console only message from OnNavigatedFrom in Fluout page (but nothing from detail page)

Expected Behavior

Correct OnNavigatedFrom method trigger on navigation from Flyout detail page

Actual Behavior

OnNavigatedFrom not triggered in detail page if navigate outside Flyout page

Basic Information

Platform: UWP
Prism: 8.1.97
XF: 5.0.0.2125

Reproduction Link

Sample App

[brianlagunas]

Closing because you did not provide the required reproduction app as defined in the issue template.

Also, please do not place multiple issues into one. Create separate issues if you have more than one

[amaneshi]

@brianlagunas Ok, not expected such strict policy (maybe this related with Hacktober fest), but no problem. Updated issue details, please reopen it.

[brianlagunas]

Well, the issue here is actually that the OnNavigatedFrom only "appears" to be called on the FlyoutPage because the Detail's NavigationPage is inheriting the BindingContext of the FlyoutPage. Which means that OnNavigatedFrom actually isn't being called on the FlyoutPage. Its being called on the NavigationPage.

The design is only the Detail should have it's a OnNavigationFrom/To called during navigation, not the VM of the FlyoutPage.

I'll have to discuss with @dansiegel about how we should solve this one..

[dansiegel]

In Xamarin.Forms, all Page's inherit from BindableBase. The way that this works is that when the BindingContext is not explicitly set then the element will default to use the BindingContext of the parent.

Given a navigation stack like MyFlyoutPage/NavigationPage/ViewA in which we do not have a ViewModel for the NavigationPage, the behavior of Xamarin.Forms is to have the NavigationPage inherit the ViewModel of it's parent MyFlyoutPage. In order to prevent this you can update your registration for the NavigationPage to be:

containerRegistry.RegisterForNavigation<NavigationPage, object>();

[brianlagunas]

After discussing with @dansiegel, we have come up with a solution that will better support this scenario when dealing with NavigationPages that have parents such as the FlyoutPage and prevent them from inheriting their parent's BindingContext. I will be submitting a PR to fix this.

[brianlagunas]

Fixed