ViewModel Kotlin Property

ViewModelProperty.kt

import androidx.appcompat.app.AppCompatActivity
import androidx.fragment.app.Fragment
import androidx.lifecycle.ViewModel
import androidx.lifecycle.ViewModelProvider
import kotlin.properties.ReadOnlyProperty
import kotlin.reflect.KProperty
import kotlin.reflect.jvm.javaType


class FragmentViewModelProperty<VM : ViewModel>(private val viewModelFactoryProvider: () -> ViewModelProvider.Factory? = { null },
                                                private val shared: Boolean)
    : ReadOnlyProperty<Fragment, VM> {

    private lateinit var cachedViewModelProvider: ViewModelProvider

    override fun getValue(thisRef: Fragment, property: KProperty<*>): VM = with(thisRef) {

        val type = property.returnType.javaType as Class<VM>
        if (!::cachedViewModelProvider.isInitialized) {
            val store = if (!shared) viewModelStore else
                requireActivity().viewModelStore
            val factory = viewModelFactoryProvider()
                    ?: if (!shared) thisRef.defaultViewModelProviderFactory else
                        requireActivity().defaultViewModelProviderFactory
            cachedViewModelProvider = ViewModelProvider(store, factory)
        }
        cachedViewModelProvider.get(type)
    }
}


class ActivityViewModelProperty<VM : ViewModel>(private val viewModelFactoryProvider: () -> ViewModelProvider.Factory? = { null })
    : ReadOnlyProperty<AppCompatActivity, VM> {

    private lateinit var cachedViewModelProvider: ViewModelProvider

    override fun getValue(thisRef: AppCompatActivity, property: KProperty<*>): VM {
        val type = property.returnType.javaType as Class<VM>
        if (!::cachedViewModelProvider.isInitialized) {
            val factory = viewModelFactoryProvider() ?: thisRef.defaultViewModelProviderFactory
            cachedViewModelProvider = ViewModelProvider(thisRef, factory)
        }
        return cachedViewModelProvider.get(type)
    }
}

inline fun <reified VM : ViewModel> Fragment.delegateViewModel(
        noinline provider: () -> ViewModelProvider.Factory? = { null },
        shared: Boolean = false) = FragmentViewModelProperty<VM>(viewModelFactoryProvider = provider, shared = shared)

inline fun <reified VM : ViewModel> AppCompatActivity.delegateViewModel(
        noinline provider: () -> ViewModelProvider.Factory? = { null }) = ActivityViewModelProperty<VM>(viewModelFactoryProvider = provider)