How to get application context everywhere in your android application using manual Dependency Injection.

AndroidManifest.xml

<Application
..........
android:name=".MyApplication"
............

AppContainer.kt

/**
 * Container of objects shared across the whole app.
 * To solve the issue of reusing objects, you can create your own dependencies container class that you use to get dependencies.
 * All instances provided by this container can be public. In the example, because you only need an instance of UserPreferences,
 * you can make its dependencies private with the option of making them public in the future if they need to be provided:
 * */

class AppContainer {

    //getting the UserPreference everywhere in our app.
    val preference by lazy { UserPreference(MyApplication.instance) }
}

GetContext.kt

//You use it anywhere in your without the need of creating the application context anytime you want it.
val contex:Context = MyApplication.instance

MyApplication.kt

/**
 * [MyApplication] is the Base class for maintaining global application state.
 * Specify fully-qualified name of this subclass as the "android:name" attribute in [AndroidManifest.xml's] <application> tag.
 * This subclass of the Application class, is instantiated before any other class when the process for your application/package is created.
 *Note: Getting application context in singletons/static fields, this leads to memory leaks (and also breaks Instant Run).
 * Why because a static variable is a variable that has been allocated "statically", meaning that its lifetime (or "extent") is the entire run of the program.
 * so this keeps copies of data or values in memory and also exposes app resources.
 *
 * The [instance] variable to provide the application context of this application without the need of always creating and instantiating context anytime we need it.
 * It allows access to application-specific resources and classes
 *
 * The [appContainer] variable get the the [AppContainer] instance
 * */

class MyApplication: Application() {

    companion object {

        //use this to get the context of this application
        lateinit var instance: MyApplication
            private set

        //getting the UserPreference everywhere in our app.
        val preference = UserPreference(instance)
    }

    override fun onCreate() {
        super.onCreate()
        instance = this
    }
    
    // Instance of AppContainer that will be used by all the Activities of the app
    //get the container like this in the activity/fragment class  val appContainer = (application as Sim2Application).appContainer
    val appContainer = AppContainer()

}