[Bug] Shell application flickering on back navigation

[RsZoli]

Description

The navigation animation is flickering, briefly displaying a black screen when navigating back in a Shell application.

Steps to Reproduce

Navigate back.

Expected Behavior

Don't flicker.

Actual Behavior

Flickering.

Basic Information

• Version with issue:
• Last known good version:
• IDE: VS 2019 16.3.9
• Platform Target Frameworks:
  • iOS: n/a
  • Android: 9.0
  • UWP: n/a
• Android Support Library Version:
• Nuget Packages:
• Affected Devices: Samsung Galaxy S8, S10

Screenshots

Slow motion video of the issue: https://i.imgur.com/bWAVzgY.mp4

Reproduction Link

[RsZoli]

A temporary workaround, if you do an override, without animation there is no flickering!

protected override bool OnBackButtonPressed() {Current.Navigation.PopAsync(false); return true;}

[jfversluis]

Hey @z07713! Thanks for report and adding the video as well as a workaround! Great job 😄

Would you by any chance also be able to put together a small reproduction project to rule out that this is caused by any other code than simply navigating?

Also, did you try this on iOS and see the same thing? Or not tried on iOS?

Thanks!

[RsZoli]

Hey @z07713! Thanks for report and adding the video as well as a workaround! Great job 😄

Would you by any chance also be able to put together a small reproduction project to rule out that this is caused by any other code than simply navigating?

Also, did you try this on iOS and see the same thing? Or not tried on iOS?

Thanks!

Hey @jfversluis , thank you for the reply, here is the repro you have asked for: https://drive.google.com/open?id=1WkGh6QwTOP380gX4RrRsksSGBoJNWeuc

Also, i have not tried this on IOS nor i have the ability to do so, i don't own a Mac.

[jfversluis]

Awesome, thanks @z07713 !

Definitely see this happening, thanks for the repro.

[djsleurink]

It might be worth noting that the workaround
protected override bool OnBackButtonPressed() {Current.Navigation.PopAsync(false); return true;}
Only works when applied inside the code behind of the AppShell.xaml and does not work when placed on seperate pages. I think this relates to 7072

[lukazh]

As a workground, overriding the OnPopAsync of ShellSection to disable animation might be more targeted.

public class CustomShellSection : ShellSection
{
	protected override Task<Page> OnPopAsync(bool animated)
	{
		return base.OnPopAsync(false); // ignore the parameter
	}
}

[jonx]

@jfversluis for me this seems to be working correctly on iOS (13.3).

Disabling the animation is not an option for us and we were just finalizing our release. We will have to rollback to 4.3 which is bad as it will reopen some bugs mostly in shell and the carousel.

We will probably have to disable some features and release without them which is sad given how long we worked on them.

Is there any workaround besides disabling animation?

Any chance this gets solved before Jan 16? Would be awesome. Thanks.

Note, the PopModal animation does not have the issue.

[jfversluis]

Sorry to hear that @jonx. Even if we were to fix it before Jan 16, it's unlikely that it will be part of a NuGet we release before then. If this is something that blocks your release I wouldn't bet on that option. Sorry about that.

[jonx]

It's okay @jfversluis, I understand, thanks for your comment. We'll just have to delay our release.
@z07713 is there a way for you to share your sample again, I can't access your links anymore. I'd like to see if it's really the same problem then I have because for me, I can briefly see appear another screen of my app instead of a black screen (it's in the context of a wizard; when I pop the current page, I see the first page of my wizard briefly). Thanks.
@jfversluis would you have an idea of what change in 4.4 introduced this problem? I'd like to see if there is a way to temporarily work around the problem. Thanks.

[jonx]

I downgraded to 4.3.991250 and I actually still have the issue, just a little less obvious (because it's faster - quicker, I suppose). I'll do more tests if @z07713 can share his example...

[RsZoli]

@jonx there you go: https://drive.google.com/open?id=19apVlQS0TafFeBT16aCfzvtvCwcweVgS

also, it has 4.3.0.991211 Forms installed :/

[tmuskopf]

I am having this issue as well. I have tried putting the line:
protected override bool OnBackButtonPressed() { Current.Navigation.PopAsync(false); return true; }
in my appShell.xaml.cs and the Flashing is still present. If someone could help me understand the work around... That would be awesome!

[lazmeister]

Happening to us as well, since 4.3 the flicker has been around on Android.

[ahmedalejo]

Just discovered this bug is on it´s one year anniversary [Shell] navigation - flickering #5755

[angelru]

The same issue here when goback, flickering screen.

For example:
https://github.com/mallibone/ShellLoginSample

[PureWeen]

Thank you for the exploration @ahmedalejo it made this one super easy to track down and fix

#10158

[PureWeen]

Once the build is done if anyone wants to test the nugets and let me know if the issue is resolved that would be helpful

https://dev.azure.com/xamarin/public/_build/results?buildId=16155&view=results

[PureWeen]

I tested the nuget with the xaminals sample

#6294

And with this nuget the flickering no longer occurs

[AndyL069]

@PureWeen Ok so I did a test:

I created a new Shell Sample App with Xamarin Forms 4.3.0.908675 -> No flickering
Then I updated to latest stable 4.5.0.495 -> Flickering
Then I updated to your newest release 4.6.0.1693 -> No flickering

Great work! Hope others will be able to confirm this.

[angelru]

@PureWeen Ok so I did a test:

I created a new Shell Sample App with Xamarin Forms 4.3.0.908675 -> No flickering
Then I updated to latest stable 4.5.0.495 -> Flickering
Then I updated to your newest release 4.6.0.1693 -> No flickering

Great work! Hope others will be able to confirm this.

@AndreasLichtsinn can't find Xamarin Forms 4.6.0.1693

[RsZoli]

@PureWeen Ok so I did a test:

I created a new Shell Sample App with Xamarin Forms 4.3.0.908675 -> No flickering
Then I updated to latest stable 4.5.0.495 -> Flickering
Then I updated to your newest release 4.6.0.1693 -> No flickering

Great work! Hope others will be able to confirm this.

@AndreasLichtsinn i can't find the 1693 build either! Also, the 4.7.0.531-nightly still flickers :/

[AndyL069]

@angelru @RsZoli It's in the published artifacts that PureWeen posted

[PureWeen]

@angelru Thank you for testing!!!!

[angelru]

@angelru Thank you for testing!!!!

@PureWeen I couldn't test, I can't download

[PureWeen]

Oh you were quoting @AndreasLichtsinn :-)

Thank you @AndreasLichtsinn for testing!!!

[AndyL069]

@angelru
Go to link:
https://dev.azure.com/xamarin/public/_build/results?buildId=16155&view=results
Click here:

Then here:

Then unpack the zip and create a local nuget package source to this folder:

Then choose this local package source and install it from there:

[angelru]

@angelru
Go to link:
https://dev.azure.com/xamarin/public/_build/results?buildId=16155&view=results
Click here:

Then here:

Then unpack the zip and create a local nuget package source to this folder:

Then choose this local package source and install it from there:

Thanks a lot!!! it works!

[tdamir]

I can confirm that there is no flicker in Xamarin Forms 4.6.0.1693.

Thanks!

[samhouts]

closed by #10158

[baneageorge]

I have the same issue with the latest Xamarin forms 4.8. I identified that on iOS the pages that have labels with TextType='Html' causes the issue...

I opened a new issue. #12385