Fragment Navigation Pattern

DataSource.kt

interface DataSourceBase

class DataSource {
    companion object {
        private var sInstance: DataSource? = null
        private var LOCK = Any()

        fun getInstance(): DataSource? {
            synchronized(LOCK) {
                if (sInstance == null) {
                    sInstance = DataSource()
                }
            }
            return sInstance
        }
    }

    private var map: WeakHashMap<Any, DataSourceBase> = WeakHashMap()

    fun <R : DataSourceBase> push(key: Any, data: R?) {
        data?.let {
            map.put(key, data)
        }
    }

    @Suppress("UNCHECKED_CAST")
    fun <R : DataSourceBase> peek(key: Any): R? {
        return map[key] as? R?
    }

    @Suppress("UNCHECKED_CAST")
    fun <R : DataSourceBase> pop(key: Any): R? {
        val data = map[key] as R
        map.remove(key)
        return data
    }

    fun remove(key: Any) {
        map.remove(key)
    }
}

FooFragment.kt

class FooFragment : BaseFragment<FooPresenter.View, FooPresenter>() {
  companion object {
        fun newInstance(data: Bar): FooFragment {
            val fragment = FooFragment()
            val bundle = Bundle()
            bundle.putParcelable("bar", data)
            fragment.arguments = bundle
            return fragment
        }
    }

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        presenter.push(arguments.getParcelable<Bar>("bar"))
    }
}

FooPresenter.kt

class FooPresenter(private val dataSource: DataSource?) : BasePresenter<FooPresenter.View> {
  
    fun push(data: Bar){
      dataSource?.push("someKey", data)
    }
  
    fun peek() : Bar {
      return dataSource?.peek<Bar>("someKey")
    }
}