New and better version of this project is available here: https://github.com/MartinXPN/SpellNote.
ProCorrector was my first android project with a terribly written codebse and several mistakes that a lot of people do while just starting to learn programming in Java and Android. This project can be a guide for someone who just starts to learn Android and wants to know what type of issues he may face and what common mistakes he shouldn't do while designing the project. Here are listed several issues present in the project:
Before this "monster" I was mostly writing code in C++ for solving competitive-programming problems like in Spoj or Codeforces, and having a C++ background I didn't have enough experience of working with Java and the codebase of ProCorrector can be described as a C++ logic written in Java. There are a lot of static helper functions, methods that were already present in java but because of not knowing about their existance I implemented them once again (like string splitting or string matching). This increases the size of code without any good consequence on performance or structure making it less maintainable.
The code of ProCorrector lacks any kind of design pattern or a paradigm. One of the bast paradigms known to me for app development are MVC or MVVM. Those come handy especially when the project gets big pretty quickly and you need some good way of organizing your logic. Also MVC and MVVM design patterns make your code more testable by decoupling views from the logic that controls them.
A lot of people while writing their first Android apps put a huge amount of logic inside activity classes. I wasn't an exception. One of the activity classes in ProCorrector contained more than 1000 lines of code. This kind of approach makes it almost impossible to change the code quickly without breaking the whole thing. Any minor change could lead to epic failures because almost everything was interconnected.
The solution is to keep views (Activities, Fragments, etc) separate from services(classes that interact with network requests or databases) and Controllers/ViewModels (classes glue logic and views together).
That was my first time working with an SQL database, therefore not having enough information about current best practices I made several mistakes. First of all, I was keeping data that was queried quite a lot without any kind of index. That tremedously slowed down time for a simple query. Secondly, I was generating queries as strings right inside the code. That made my code not very readable while increasing the risk of messing up something while working with strings (for performance reasons I was using StringBuilders that are not thread-safe while working with threads).
A better way would be to choose a good ORM library that can satisfy all your needs and prceed with it. OrmLite, SugarORM, and Realm are currently considered as one of the bests. I've used Realm in my other project.
Despite having this many issues this project was downloaded more than 100.000 times while being in play store for about a year. Here is the link to the project in play store: https://play.google.com/store/apps/details?id=com.ProCorrector.XPN.procorrector&hl=en