How to have Android Gradle build write a file that goes into the debug APK

Issue

GenyMotion's localhost IP address (10.0.3.2) is different from the Android emulator's localhost IP (10.0.2.2). Currently I have this in one of my source files:

//val LOCALHOST = "10.0.2.2"  // Android emulator
val LOCALHOST = "10.0.3.2"  // Genymotion

and whenever I switch between a Linux box and a Mac box and fetch the latest sources, I have to uncomment one and comment the other before rebuilding.

Unless someone can think of a better solution, I would like to have a Gradle task that writes out one of these values depending on the host OS, into a file that's included in the APK in such a way that I can access it from my Android app's runtime, and have that task run before assembleDebug when I build in Android Studio.

I suppose putting it in a resource would be easiest to access on the runtime side, but even a plain text file accessible to Class.getResourceAsStream() would be fine too.

I don't mind if it's included in the release apk, but I'd prefer that it just go into the debug ones.

I would also prefer that the file be generated in my build/ output directory, so that it's invisible to version control.

Any idea how to go about this?

Solution

There are much better solutions like finding the local IP address using getNetworkInterfaces(), but as you asked how to pass some information from gradle,

android {
    productFlavors {
        flavorGenymotion {
            buildConfigField "String", "LOCALHOST", '"10.0.3.2"'
        }
        flavorEmulator {
            buildConfigField "String", "LOCALHOST", '"10.0.2.2"'
        }
    }
    ...

which you can access as BuildConfig.LOCALHOST.

Answered By - Diego Torres Milano