Binding to AAR library 'com.sunmi printerlibrary' gives lots of 'Class has invalid base type' errors

[HansOlavS]

Error Message or Issue

warning BG8103: Class 'Com.Sunmi.Peripheral.Printer.InnerLcdCallback' has invalid base type 'com.sunmi.peripheral.printer.ILcdCallback.Stub'.

(There's also lots of other classes with invalid base types...)

Version Information

N/A

Other Helpful Info

printerlibrary-1.0.14.aar.zip

Please note that the aar file is just renamed to aar.zip - it's not actually a zip file!

[HansOlavS]

I'm not sure why all my version info disappeared, but here it is:

Microsoft Visual Studio Community 2019
Version 16.11.3
VisualStudio.16.Release/16.11.3+31702.278
Microsoft .NET Framework
Version 4.8.04084

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Azure App Service Tools v3.0.0 16.11.75.64347
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Azure Data Lake Tools for Visual Studio 2.6.1000.0
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Azure Functions and Web Jobs Tools 16.11.75.64347
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Azure Stream Analytics Tools for Visual Studio 2.6.1000.0
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Microsoft Azure Service Fabric Tools for Visual Studio

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SQL Server Data Tools 16.0.62107.28140
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Visual F# Tools 16.11.0-beta.21322.6+488cc578cafcd261d90d748d8aaa7b8b091232dc
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Xamarin 16.11.000.175 (d16-11@e140e23)
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Xamarin.iOS and Xamarin.Mac SDK 14.20.0.25 (3b53e529b)
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[jpobst]

This means there is something wrong trying to bind the com.sunmi.peripheral.printer.ILcdCallback.Stub type, which Com.Sunmi.Peripheral.Printer.InnerLcdCallback depends on.

There is a lot of information about debugging this issue here: https://github.com/xamarin/java.interop/wiki/Troubleshooting-Android-Bindings-Issues.

You will need to examine the diagnostic build log and find the message telling you what issue it is hitting binding com.sunmi.peripheral.printer.ILcdCallback.Stub.

[HansOlavS]

Thanks, I'll try that and update this issue if I'm able to resolve it or not.

[HansOlavS]

Thanks a lot @jpobst!, I got that fixed 😊
I can see that the classes I need are marked with visibility="" in the api.xml file. I've fixed those with <attr> tags in the Metadata.xml file, but now I'm stuck with these warnings:

• Com.Sunmi.Peripheral.Printer.ICallback.cs(120,30,120,40): warning CS0114: 'CallbackStub.OnTransact(int, Parcel, Parcel, int)' hides inherited member 'Binder.OnTransact(int, Parcel, Parcel?, int)'. To make the current member override that implementation, add the override keyword. Otherwise add the new keyword.
• Com.Sunmi.Peripheral.Printer.ISunmiPrinterService.cs(2157,30,2157,40): warning CS0114: 'SunmiPrinterServiceStub.OnTransact(int, Parcel, Parcel, int)' hides inherited member 'Binder.OnTransact(int, Parcel, Parcel?, int)'. To make the current member override that implementation, add the override keyword. Otherwise add the new keyword.
• ILcdCallback.cs(120,30,120,40): warning CS0114: 'LcdCallbackStub.OnTransact(int, Parcel, Parcel, int)' hides inherited member 'Binder.OnTransact(int, Parcel, Parcel?, int)'. To make the current member override that implementation, add the override keyword. Otherwise add the new keyword.
• ITax.cs(120,30,120,40): warning CS0114: 'TaxStub.OnTransact(int, Parcel, Parcel, int)' hides inherited member 'Binder.OnTransact(int, Parcel, Parcel?, int)'. To make the current member override that implementation, add the override keyword. Otherwise add the new keyword.

Any easy way to fix that via Metadata.xml or otherwise? Or maybe it's not really an issue at all and I can ignore it? 🤔

[jpobst]

They are warnings, so you can ignore them if you want.

We added this metadata to allow you to fix them, but I don't think it ever got properly documented: dotnet/java-interop#701

[HansOlavS]

Thanks again, @jpobst! I tried to use that but I got this error:

• 'SunmiPrinterServiceStub.OnTransact(int, Parcel, Parcel, int)': cannot change access modifiers when overriding 'protected' inherited member 'Binder.OnTransact(int, Parcel, Parcel?, int)'

Hopefully this will work just fine with the warnings. I'll give it the good old college try! Thanks for the excellent help!

[jpobst]

You would probably need to change the visibility to protected to match the base method.

Glad you got it working!

[HansOlavS]

@jpobst Just for the record: You were right, setting the visibility to protected made everything work as a charm! Peace out!

Thanks so much for the extremely helpful tips and lightning speed! 🙏