Look Counter app is now in Kotlin and stores data in Room DB

In 2016 (which seems like a whole eternity from now :), I wrote an Android app called Look Counter for counting how many times you have switched the screen on, as well as unlocked it. Up until recently I haven’t updated it. The app used such libs as greenDAO , ButterKnife , GoogleAnalytics, and RecyclerView. After the update, only the last one remained 🙂

I’ve decided to completely re-write Look Counter, using the modern tools. The first step was to update all of the dependencies and set project’s target API to 27. It’s a good idea to set yours to 26 as a min, because of Google Play’s new requirements — “Google Play will require that new apps target at least Android 8.0 (API level 26) from August 1, 2018, and that app updates target Android 8.0 from November 1, 2018.”

As the second step I chose to refactor layouts and use ConstraintLayout in order to flatten the hierarchy. It allowed me to make both Calendar and About screens completely flat, which I think is awesome 🙂

Next I wanted to convert Java to Kotlin. I used Android Studio’s Convert Java file to Kotlin file option, and then cleaned up the code. I got rid of !! and used vals instead of vars whenever possible. Also, objects instead of classes, extension methods, etc. In general, simply converting Java to Kotlin is easy, but to make Kotlin code look good and not like some Java-adaption, requires an extra effort.

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Database example app with Room ORM

With Android Architecture Components getting a stable 1.0 version, there are now no excuses of not using it 🙂 Along with handling lifecycle events, realtime data updates in UI (ViewModel with LiveData) and pagination of loaded data (Paging), comes Room – small, yet powerful SQLite ORM. In this post I’m gonna demonstrate its core capabilities on an example Android application.

Remember those times implementing SQLiteOpenHelper and checking SQL queries in run-time? Good news is that you don’t have to do it anymore! Room performs compile-time checks on your SQL queries and you don’t have to write any SQLite code which is not in a direct relation with your data queries. Great, lets use it!

First of all, Room is a part of Architecture Components, which means it works really well with ViewModel, LiveData and Paging (but does not depend on them!). Also, RxJava and Kotlin are perfectly fine too. In order to add Room to the project, I’m adding the following lines in app’s build.gradle file:

    // Room
    implementation "android.arch.persistence.room:runtime:1.0.0"
    annotationProcessor "android.arch.persistence.room:compiler:1.0.0"

Check for the latest library version here.

Additionally, provide a location of DB’s schema in defaultConfig scope. This way you can always check how it looks, maybe decide to modify your tables once you notice something in scheme.

   javaCompileOptions {
        annotationProcessorOptions {
            arguments = ["room.schemaLocation":
                                 "$projectDir/schemas".toString()]
        }
    }

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