I've suggested this before, so I found a master programmer who had 20 years of BASIC programmming expericence and has written books on the subject. The below book I read and is top notch (I have read several books on VB and this is a easy one to learn from). Here's a suggestion to contact about getting a professional book made about b4a. Only Erel can do this. I did send him an email about this, but really this has to go through Erel. I cant even figure out how to get a database going to finsih a program i wrote.
James Foxall "Sams teach yourself visual basic in 24 hours"
Despite the difference in the title, the contents of "B4A Ultra" is in fact the same as the 2015 edition of "B4A Rapid Android App Development using BASIC". It covers version 5.50 of B4A.
Unless you need a hard-wearing book for a public or university library, I would recommend purchase of the paperback or ebook, both of which are always the latest editions (currently covering B4A 6.00).
Yes Ralph, it is really a true Kindle book and not a PDF or other format, although it is also available in PDF and EPUB formats too from http://pennypress.co.uk/?page_id=11.