I am sure the following will help you in getting to know the best about converting Android apps into iOS.
1) In case you have written your app in C/C++ using JNI, you can write a wrapper. You can also interface it with the Apple operating system (i.e. providing callbacks from iOS to the written function in JNI). There are numerous frameworks out that can help you do this in easy manner, I am sure you will find some issues in integrating the app and then adapting it to the framework and not forgetting that the app must be written in C or C++.
2) You need to rewrite it for Apple OS. I am not able to find good tools that that can help you in converting the Android app into iOS. Also, there may not be any software that can do it as there is a variety of apps written in different APIs.
3) There are few converters that can help you in converting Java apps into C or C++ but thy will not help if there see difference in APIs. also, there may times come when struggle when you try to convert your code you are working (i.e. on same API) rather than rewriting it in IOS or for any other Operating system.
The whole place of issue in converting the apps lies in services and the type of APIs we are using. I have not looked into such stuff yet but there are APIs that work properly on Android but not in iOS.
Utilizing C/C++ and locally aggregating it for the perfect platform resembles the best approach for Android-ios-Win7mobile cross-stage advancement. This gets you to some degree an application central core which you can use to do the real application rationale.
With respect to the OS particular parts (APIs) that your application is utilizing, you’ll need to set up correspondence interfaces in the middle of them and your application’s core part.