Getting a NullReferenceException in Android when backing out of app

ryanbuening · September 2019

I'm using Xamarin Forms 4.2.0 and utilizing Xamarin.Forms Shell. Pressing the back button seems to work find when navigating through the various screens in my app, however, when I press back to exit the app when debugging I get a NullReferenceException:

09-30 14:49:52.866 D/Mono    ( 1085): Loading reference 10 of /storage/emulated/0/Android/data/com.companyname.agentconnectmobile/files/.__override__/Xamarin.Forms.Platform.Android.dll asmctx DEFAULT, looking for System.Runtime.Serialization, Version=2.0.5.0, Culture=neutral, PublicKeyToken=abc123
09-30 14:49:52.866 D/Mono    ( 1085): Assembly Ref addref Xamarin.Forms.Platform.Android[0x799acc0e00] -> System.Runtime.Serialization[0x7935aa8d00]: 3
09-30 14:49:52.866 D/Mono    ( 1085): Loading reference 1 of System.Runtime.Serialization.dll asmctx DEFAULT, looking for System.Xml, Version=2.0.5.0, Culture=neutral, PublicKeyToken=abc123
09-30 14:49:52.866 D/Mono    ( 1085): Assembly Ref addref System.Runtime.Serialization[0x7935aa8d00] -> System.Xml[0x799be73480]: 5
09-30 14:49:52.918 D/Mono    ( 1085): Loading reference 2 of System.Runtime.Serialization.dll asmctx DEFAULT, looking for System.ServiceModel.Internals, Version=0.0.0.0, Culture=neutral, PublicKeyToken=abc123
09-30 14:49:52.920 D/Mono    ( 1085): Image addref System.ServiceModel.Internals[0x7937f9df00] (asmctx DEFAULT) -> System.ServiceModel.Internals.dll[0x7935889800]: 2
09-30 14:49:52.920 D/Mono    ( 1085): Prepared to set up assembly 'System.ServiceModel.Internals' (System.ServiceModel.Internals.dll)
09-30 14:49:52.920 D/Mono    ( 1085): Assembly System.ServiceModel.Internals[0x7937f9df00] added to domain RootDomain, ref_count=1
09-30 14:49:52.922 D/Mono    ( 1085): AOT: image 'System.ServiceModel.Internals.dll.so' not found: dlopen failed: library "System.ServiceModel.Internals.dll.so" not found
09-30 14:49:52.923 D/Mono    ( 1085): AOT: image '/Users/builder/jenkins/workspace/archive-mono/2019-06/android/release/sdks/out/android-arm64-v8a-release/lib/mono/aot-cache/arm64/System.ServiceModel.Internals.dll.so' not found: (null)
09-30 14:49:52.923 D/Mono    ( 1085): Config attempting to parse: 'System.ServiceModel.Internals.dll.config'.
09-30 14:49:52.923 D/Mono    ( 1085): Config attempting to parse: '/Users/builder/jenkins/workspace/archive-mono/2019-06/android/release/sdks/out/android-arm64-v8a-release/etc/mono/assemblies/System.ServiceModel.Internals/System.ServiceModel.Internals.config'.
09-30 14:49:52.923 D/Mono    ( 1085): Assembly Ref addref System.Runtime.Serialization[0x7935aa8d00] -> System.ServiceModel.Internals[0x7937f9df00]: 2
09-30 14:49:52.923 D/Mono    ( 1085): Loading reference 0 of System.ServiceModel.Internals.dll asmctx DEFAULT, looking for mscorlib, Version=2.0.5.0, Culture=neutral, PublicKeyToken=abc123
09-30 14:49:52.923 D/Mono    ( 1085): Assembly Ref addref System.ServiceModel.Internals[0x7937f9df00] -> mscorlib[0x7a3039be80]: 64
09-30 14:49:52.923 D/Mono    ( 1085): Loading reference 2 of System.ServiceModel.Internals.dll asmctx DEFAULT, looking for System.Xml, Version=2.0.5.0, Culture=neutral, PublicKeyToken=abc123
09-30 14:49:52.924 D/Mono    ( 1085): Assembly Ref addref System.ServiceModel.Internals[0x7937f9df00] -> System.Xml[0x799be73480]: 6
Loaded assembly: System.ServiceModel.Internals.dll [External]09-30 14:49:52.924 D/Mono    ( 1085): Loading reference 3 of System.Runtime.Serialization.dll asmctx DEFAULT, looking for System, Version=2.0.5.0, Culture=neutral, PublicKeyToken=abc123

09-30 14:49:52.924 D/Mono    ( 1085): Assembly Ref addref System.Runtime.Serialization[0x7935aa8d00] -> System[0x799acd1580]: 10
09-30 14:49:52.998 D/Mono    ( 1085): Loading reference 1 of System.Xml.dll asmctx DEFAULT, looking for System, Version=2.0.5.0, Culture=neutral, PublicKeyToken=abc123
09-30 14:49:52.999 D/Mono    ( 1085): Assembly Ref addref System.Xml[0x799be73480] -> System[0x799acd1580]: 11
09-30 14:49:53.099 D/Mono    ( 1085): Loading reference 1 of System.ServiceModel.Internals.dll asmctx DEFAULT, looking for System, Version=2.0.5.0, Culture=neutral, PublicKeyToken=abc123
09-30 14:49:53.100 D/Mono    ( 1085): Assembly Ref addref System.ServiceModel.Internals[0x7937f9df00] -> System[0x799acd1580]: 12
09-30 14:49:53.145 D/Mono    ( 1085): Loading reference 19 of /storage/emulated/0/Android/data/com.companyname.agentconnectmobile/files/.__override__/Xamarin.Forms.Platform.Android.dll asmctx DEFAULT, looking for System.Xml, Version=2.0.5.0, Culture=neutral, PublicKeyToken=abc123
09-30 14:49:53.146 D/Mono    ( 1085): Assembly Ref addref Xamarin.Forms.Platform.Android[0x799acc0e00] -> System.Xml[0x799be73480]: 7
09-30 14:49:53.221 D/Mono    ( 1085): DllImport searching in: 'libmono-native.so' ('./libmono-native.so').
09-30 14:49:53.221 D/Mono    ( 1085): Searching for 'SystemNative_Unlink'.
09-30 14:49:53.221 D/Mono    ( 1085): Probing 'SystemNative_Unlink'.
09-30 14:49:53.222 D/Mono    ( 1085): Found as 'SystemNative_Unlink'.
09-30 14:49:53.279 D/Mono    ( 1085): DllImport searching in: 'libmono-native.so' ('./libmono-native.so').
09-30 14:49:53.279 D/Mono    ( 1085): Searching for 'SystemNative_LStat2'.
09-30 14:49:53.279 D/Mono    ( 1085): Probing 'SystemNative_LStat2'.
09-30 14:49:53.279 D/Mono    ( 1085): Found as 'SystemNative_LStat2'.
09-30 14:49:53.279 D/Mono    ( 1085): DllImport searching in: 'libmono-native.so' ('./libmono-native.so').
09-30 14:49:53.279 D/Mono    ( 1085): Searching for 'SystemNative_Rename'.
09-30 14:49:53.279 D/Mono    ( 1085): Probing 'SystemNative_Rename'.
09-30 14:49:53.280 D/Mono    ( 1085): Found as 'SystemNative_Rename'.
09-30 14:49:53.553 D/Mono    ( 1085): DllImport searching in: 'libmono-native.so' ('./libmono-native.so').
09-30 14:49:53.553 D/Mono    ( 1085): Searching for 'SystemNative_Link'.
09-30 14:49:53.553 D/Mono    ( 1085): Probing 'SystemNative_Link'.
09-30 14:49:53.553 D/Mono    ( 1085): Found as 'SystemNative_Link'.
09-30 14:49:53.563 D/Mono    ( 1085): DllImport searching in: 'libmono-native.so' ('./libmono-native.so').
09-30 14:49:53.563 D/Mono    ( 1085): Searching for 'SystemNative_Stat2'.
09-30 14:49:53.563 D/Mono    ( 1085): Probing 'SystemNative_Stat2'.
09-30 14:49:53.563 D/Mono    ( 1085): Found as 'SystemNative_Stat2'.
09-30 14:49:53.564 D/Mono    ( 1085): DllImport searching in: 'libmono-native.so' ('./libmono-native.so').
09-30 14:49:53.564 D/Mono    ( 1085): Searching for 'SystemNative_Symlink'.
09-30 14:49:53.564 D/Mono    ( 1085): Probing 'SystemNative_Symlink'.
09-30 14:49:53.564 D/Mono    ( 1085): Found as 'SystemNative_Symlink'.
09-30 14:49:53.588 W/com.companyname.agentconnectmobile( 1085): type=1400 audit(0.0:4414): avc: denied { link } for comm=54687265616420506F6F6C20576F72 name="PropertyStore.forms.tmp" dev="dm-6" ino=77573 scontext=u:r:untrusted_app_27:s0:c6,c257,c512,c768 tcontext=u:object_r:app_data_file:s0:c6,c257,c512,c768 tclass=file permissive=0
09-30 14:49:53.597 D/Mono    ( 1085): DllImport searching in: 'libmono-native.so' ('./libmono-native.so').
09-30 14:49:53.598 D/Mono    ( 1085): Searching for 'SystemNative_CopyFile'.
09-30 14:49:53.598 D/Mono    ( 1085): Probing 'SystemNative_CopyFile'.
09-30 14:49:53.598 D/Mono    ( 1085): Found as 'SystemNative_CopyFile'.
**System.NullReferenceException:** 'Object reference not set to an instance of an object.'

This is my first Xamarin application so I'm not sure if I am supposed to be handling exit on Android somehow? I haven't seen this issue on iOS.

LeonLu · October 2019

If you click the back button to exit the apllcation in android, It means that you close this application, not make the application to the background.

I think when you see the following log, it means that your application is closed. I think that you do not need to handle the **System.NullReferenceException:** 'Object reference not set to an instance of an obj

   09-30 14:49:53.588 W/com.companyname.agentconnectmobile( 1085): type=1400 audit(0.0:4414): avc: denied { link } for comm=54687265616420506F6F6C20576F72 name="PropertyStore.forms.tmp" dev="dm-6" ino=77573 scontext=u:r:untrusted_app_27:s0:c6,c257,c512,c768 tcontext=u:object_r:app_data_file:s0:c6,c257,c512,c768 tclass=file permissive=0

igorkr_10 · October 2019

I have same issue but don't have enough time to deal with it.
What concrete steps we can do to avoid this problem?

AlbertK · October 2019

It is a big bad bug. I can't deploy with Form 4.2 as it is a show stopper.

https://github.com/xamarin/Xamarin.Forms/issues/7327

ryanbuening · October 2019

Hey, sorry for the delayed response. Check this out and see if it fixes the issue for you guys: https://stackoverflow.com/questions/58173920/getting-a-nullreferenceexception-in-xamarin-forms-on-android-when-backing-out-of/58180603#58180603

igorkr_10 · October 2019

@ryanbuening said:
Hey, sorry for the delayed response. Check this out and see if it fixes the issue for you guys: https://stackoverflow.com/questions/58173920/getting-a-nullreferenceexception-in-xamarin-forms-on-android-when-backing-out-of/58180603#58180603

Good try, but this workaround closes application completely. Standard behavior just put it to sleep.

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