Yes and no.
iOS is a different operating system you need to learn it.
All the code related to it is different and all the other code is the same.
Or must I rewrite my apps?
Not all, the operating system routines must be rewritten.
For the layout files Erel has written a program to convert them.
You can have a look at the B4i Beginner's Guide, it's structure is the same as the B4A Beginner's Guide.
It has a chapter with the differences between B4A and B4i.
I have ported the programs in the guide and the SQLIteLight examples from B4A to B4i.
You may have a look at the differences.