UPDATE: Commercial RoboVM has nice tutorial about IB (still available today). OOS RoboVM implementation has own differences and these are covered in this post. It is not possible to use Java classes with Interface Builder directly. To workaround this dummy objective-c XCode project is generated. This project contains:
UPDATE2: web archive

In RoboVM’s cocoatouch there are bunch of NSError subclasses that don’t exist in objc iOS itself. For example WKError This is hand written class required to allow RoboVM’s NSError return object error code which can be used to compare against enum members, such as WKErrorCode.
NSError provides information by following properties:

UPDATE: another workarounds explained in new post
A try to use BC within idea plugging ends with following:

Caused by: java.lang.SecurityException: JCE cannot authenticate the provider BC
	at javax.crypto.Cipher.getInstance(Cipher.java:657)
	at javax.crypto.Cipher.getInstance(Cipher.java:596)
	at org.bouncycastle.jcajce.util.NamedJcaJceHelper.createCipher(Unknown Source)
	... 97 more
Caused by: java.util.jar.JarException: Class is on the bootclasspath
	at javax.crypto.JarVerifier.verify(JarVerifier.java:247)
	at javax.crypto.JceSecurity.verifyProviderJar(JceSecurity.java:160)
	at javax.crypto.JceSecurity.getVerificationResult(JceSecurity.java:186)
	at javax.crypto.Cipher.getInstance(Cipher.java:653)
	... 99 more

This was happening with RoboVM idea plugin but in general issue is wider. First thing attempt to fix it includes:

bro-gen received several updates and new features during handling iOS11 bindings, mostly fixes but there are new ones.

It is not too big task to create java binding for custom framework as bro-gen semiautomatic tool available. This step-by-step tutorial explains how quickly generate binding using recently added suggestion feature. Admob is used here as an example framework.

History Add debugging support to Eclipse #171
Fix fixed source lookup problem for eclipse. #223

Problem in JdwpRefTypeSourceFileHandler.Handle():52 as it was generating full file path. But by spec it is shell not.

History java constructor is not called in UIApplicationDelegate implementation #221
Fix PR #222

UIApplicationDelegate is being created from native side. And it is constructor is not called so all instance members are not initialized. Yep same #894. But why?

History AReference to java object is not maintained by objc, when the java object is garbage collected #217
Fix PR fixed #217 #219

The problem is that ObjCObject keep reference of native object pointer (peer) to java object in map where java object is maintained in week reference vo. As result all java objects that is not referenced at Java side are subject for GC. And this is wrong.