Kotlin singleton application class

Issue

On Android I want to make my application class a singleton.

Making it like this:

object MyApplication: Application(){}

won't work. The following error is thrown at runtime:

java.lang.IllegalAccessException: private com....is not accessible from class android.app.Instrumentation.

Doing this is also not possible:

class MyApp: Application() {

    private val instance_: MyApp

    init{
        instance_ = this
    }

    override fun onCreate() {
        super.onCreate()
        if (BuildConfig.DEBUG) {
            Timber.plant(Timber.DebugTree());
        }
    }

    companion object{
        fun getInstance() = instance_
    }
}

How can I get an instance of my application class everywhere in my app? I would like to use MyApp.instance() instead of (applicationContext as MyApp).

Also an explanation why I want this: I have classes in my app. For example, a SharedPreference Singleton which is initialised with a context, and as it’s a singleton, it can't have arguments.

Solution

If you want to use it to access some static properties you have there: You will only have one instance of your Application, so simply use the name you gave to the class. Don't worry about it not being an actual singleton, you can use it the same way.

Example:

class MyApp : Application() {

    companion object {
        const val CONSTANT = 12
        lateinit var typeface: Typeface
    }

    override fun onCreate() {
        super.onCreate()
        typeface = Typeface.createFromAsset(assets, "fonts/myFont.ttf")
    }

}

Then you can use MyApp.CONSTANT and MyApp.typeface anywhere in your app.

-

If what you want is to use it as an application context you can create an extension property for Context:

val Context.myApp: MyApp
        get() = applicationContext as MyApp

Then you can use myApp to get the the application context anywhere you have a context.

Answered By - nitrico