Link Error

I tried to use your library but with no luck. I got the following error:

Undefined symbols for architecture arm64:
"_OBJC_CLASS_$_Hero", referenced from:
objc-class-ref in registrar.o
ld: symbol(s) not found for architecture arm64
clang : error : linker command failed with exit code 1 (use -v to see invocation)

MTOUCH : error MT5211: Native linking failed, undefined Objective-C class: Hero. The symbol '_OBJC_CLASS_$_Hero' could not be found in any of the libraries or frameworks linked with your application.
MTOUCH : warning MT5215: References to 'Kernel32' might require additional -framework=XXX or -lXXX instructions to the native linker
MTOUCH : warning MT5215: References to 'libEGL' might require additional -framework=XXX or -lXXX instructions to the native linker
MTOUCH : error MT5202: Native linking failed. Please review the build log.
Done building target "_CompileToNative" in project "....iOS.csproj" -- FAILED.

Done building project "....iOS.csproj" -- FAILED.

Build FAILED.

.../packages/Microsoft.Bcl.Build.1.0.21/build/Microsoft.Bcl.Build.targets(243,5): warning : All projects referencing ....csproj must install nuget package Microsoft.Bcl.Build. For more information, see http://go.microsoft.com/fwlink/?LinkID=317569.
/Library/Frameworks/Mono.framework/Versions/5.0.1/lib/mono/msbuild/15.0/bin/Microsoft.Common.CurrentVersion.targets(1980,5): warning MSB3276: Found conflicts between different versions of the same dependent assembly. Please set the "AutoGenerateBindingRedirects" property to true in the project file. For more information, see http://go.microsoft.com/fwlink/?LinkId=294190.
ViewControllers/LoginViewController/LoginViewController.cs(99,13,106,31): warning CS1702: Assuming assembly reference 'System.Reactive.Core, Version=3.0.1000.0, Culture=neutral, PublicKeyToken=94bc3704cddfc263' used by '...' matches identity 'System.Reactive.Core, Version=3.0.3000.0, Culture=neutral, PublicKeyToken=94bc3704cddfc263' of 'System.Reactive.Core', you may need to supply runtime policy
.../obj/iPhone/Debug/device-builds/iphone7.1-10.3.2/mtouch-cache/registrar.m(20159,11): warning GD811092D: duplicate protocol definition of 'CALayerDelegate' is ignored
MTOUCH : warning MT5215: References to 'Kernel32' might require additional -framework=XXX or -lXXX instructions to the native linker
MTOUCH : warning MT5215: References to 'libEGL' might require additional -framework=XXX or -lXXX instructions to the native linker
clang : error : linker command failed with exit code 1 (use -v to see invocation)
MTOUCH : error MT5211: Native linking failed, undefined Objective-C class: Hero. The symbol '_OBJC_CLASS_$_Hero' could not be found in any of the libraries or frameworks linked with your application.
MTOUCH : error MT5202: Native linking failed. Please review the build log.
6 Warning(s)
3 Error(s)

Time Elapsed 00:00:44.72

---------------------- Done ----------------------

Build: 3 errors, 7 warnings