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public open class AndroidViewModelFactory
    private constructor(
        private val application: Application?,
        // parameter to avoid clash between constructors with nullable and non-nullable
        // Application
        @Suppress("UNUSED_PARAMETER") unused: Int,
    ) : NewInstanceFactory() {
        /**
         * Constructs this factory. When a factory is constructed this way, a component for which
         * [ViewModel] is created must provide an [Application] by [APPLICATION_KEY] in
         * [CreationExtras], otherwise [IllegalArgumentException] will be thrown from [create]
         * method.
         */
        @Suppress("SingletonConstructor")
        public constructor() : this(application = null, unused = 0)
        /**
         * Constructs this factory.
         *
         * @param application an application to pass in [AndroidViewModel]
         */
        @Suppress("SingletonConstructor")
        public constructor(application: Application) : this(application, unused = 0)
        @Suppress("DocumentExceptions")
        override fun <T : ViewModel> create(modelClass: Class<T>, extras: CreationExtras): T {
            return if (application != null) {
                create(modelClass)
            } else {
                val application = extras[APPLICATION_KEY]
                if (application != null) {
                    create(modelClass, application)
                } else {
                    // For AndroidViewModels, CreationExtras must have an application set
                    if (AndroidViewModel::class.java.isAssignableFrom(modelClass)) {
                        throw IllegalArgumentException(
                            "CreationExtras must have an application by `APPLICATION_KEY`"
                        )
                    }
                    super.create(modelClass)
                }
            }
        }
        @Suppress("DocumentExceptions")
        override fun <T : ViewModel> create(modelClass: Class<T>): T {
            return if (application == null) {
                throw UnsupportedOperationException(
                    "AndroidViewModelFactory constructed " +
                        "with empty constructor works only with " +
                        "create(modelClass: Class<T>, extras: CreationExtras)."
                )
            } else {
                create(modelClass, application)
            }
        }
        @Suppress("DocumentExceptions")
        private fun <T : ViewModel> create(modelClass: Class<T>, app: Application): T {
            return if (AndroidViewModel::class.java.isAssignableFrom(modelClass)) {
                try {
                    modelClass.getConstructor(Application::class.java).newInstance(app)
                } catch (e: NoSuchMethodException) {
                    throw RuntimeException("Cannot create an instance of $modelClass", e)
                } catch (e: IllegalAccessException) {
                    throw RuntimeException("Cannot create an instance of $modelClass", e)
                } catch (e: InstantiationException) {
                    throw RuntimeException("Cannot create an instance of $modelClass", e)
                } catch (e: InvocationTargetException) {
                    throw RuntimeException("Cannot create an instance of $modelClass", e)
                }
            } else super.create(modelClass)
        }
        public companion object {
            private var _instance: AndroidViewModelFactory? = null
            /**
             * Retrieve a singleton instance of AndroidViewModelFactory.
             *
             * @param application an application to pass in [AndroidViewModel]
             * @return A valid [AndroidViewModelFactory]
             */
            @JvmStatic
            public fun getInstance(application: Application): AndroidViewModelFactory {
                if (_instance == null) {
                    _instance = AndroidViewModelFactory(application)
                }
                return _instance!!
            }
            /**
             * A [CreationExtras.Key] to query an application in which ViewModel is being created.
             */
            @JvmField public val APPLICATION_KEY: Key<Application> = CreationExtras.Companion.Key()
        }
    }
    ```