I am junior xamarin.forms developer. I faced with many work vacancies, these has a requirement to know Android/iOS SDK's or both. And good custom renders and platform specific features requires to know SDK's. I want to learn theme from scratch and to deep, because I haven't android/iOS programming background. So, my quistion is: Where I can learn this without too many java/swift/objectC code but with many SDK's info? Sorry for so general question.