Xamarin.forms: [Bug] Shell Application crash when clicking hardware back button on android

[ColeXm]

Description

Shell Application crash when clicking hardware back button on android (back to device homepage), the error shows System.NullReferenceException, but it occurs on latest Xamarin.Forms (4.2.0.709249) , i test with the version 4.1.0.555618 and no crash happens , i think it's a bug.

Steps to Reproduce

1. Download official sample :https://docs.microsoft.com/en-us/samples/xamarin/xamarin-forms-samples/userinterface-xaminals/ .
2. Upload Xamarin.Forms to the latest .
3. Test on android, when locates at root page , click hardware back button .

Expected Behavior

Back to HomePage of mobile phone.

Actual Behavior

Crash occurs.

Basic Information

• IDE: Visual studio 2019 16.1.3
• Xamarin.Android : 9.3.0.22
• Nuget Packages: Xamarin.Forms (4.2.0.709249)

Screenshots

[BrunoLogan]

I'm having the same issue but on 4.1.0.709244

[chrisparkeronline]

Just adding a tad bit to this. I get "System.NullReferenceException: 'Object reference not set to an instance of an object.'" when using the hardware back button.

[Sauder91]

Probably already seen something like this but this is the stack trace I'm getting.

[raevenbauto]

I'm having the same issue 4.2.0.709249. I tried downgrading to 4.1.0.555618as mentioned by @ColeXm and no issues.

[adrianknight89]

This is a duplicate of #6640.

6715 fixes that.

@PureWeen I wanted to submit a quick fix for this, but looks like @kvpt took a deeper dive.

[polieadie]

I was using version 4.2.0.815419 and I was having the same issue.
I downgrade to 4.1.0.555618 as mentioned by @raevenbauto then by @ColeXm and i don't have the issue anymore.

I am still hoping to use the latest version though.
Does it have a fix already?

[adamsproul]

Same experience as @polieadie & @raevenbauto

I had to downgrade Xamarin.Forms.Maps before Xamarin.Forms in order to downgrade successfully.

4.2.0.815419 --> 4.1.0.555618

[mryll]

I have the same problem.

Xamarin.Forms: 4.2.0.815419

I had to disable the back button so it doesn't go to the home page.

[pengalo]

Microsoft, have you reproduced this issue? This is now a blocker for me because the previous versions have a bug with custom shell title (Shell.TitleView) where it obscures the top of the main page content. I can't release with either bug.

[PureWeen]

@pengalo fixed by

https://github.com/xamarin/Xamarin.Forms/pull/7768

[polieadie]

I just tried with version 4.2.0.848062 (latest).
Still the same problem with back button.
I have no choice but to go back to 4.1.0.555618.

Do we have a timeline when this will be solved on a released version?

[pichow]

Same here with 4.2.0.709249

... so thought I'd try with 4.3.0.947036 (latest stable) ... same problem still exists

[gonzalesgm-git]

its still a problem in 4.4.0.991265

[kvpt]

Can someone provide a basic reproduction, because the reproduction case provided in #6640 seem fixed.

From the stack trace in https://github.com/xamarin/Xamarin.Forms/issues/7327#issuecomment-530214066, the issue seem triggered by the fragment destroy.

In my PR (#6715) I replaced all destroy with dispose, so I'm almost sure that it will fix the issue.
I rebased the changes on top of the 4.4 branch.
If someone can test that, need to rename the zip to nupkg.
Xamarin.Forms.4.4.99.zip

If it works I will resurrect this PR.

[PureWeen]

I tested this with the latest Xaminals that has XF 4.5 and I'm not seeing a crash anymore

[polieadie]

I just tested this now and I still can reproduce the problem with version 4.5.
Going back again to version 4.1.0.555618.