Make an object survive configuration changes. Replacement for onRetainCustomNonConfigurationInstance

LongLastingElement.kt

/*
 * Copyright 2019 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

class LongLastingElement<T> : ViewModel() {

    private var element: T? = null

    fun getElement(elementProducer: () -> T): T {
        return element ?: elementProducer.invoke().also {
            element = it
        }
    }

    @Suppress("UNCHECKED_CAST")
    companion object {
        private class LongLastingElementFactory :
            ViewModelProvider.Factory {
            override fun <T : ViewModel?> create(modelClass: Class<T>): T {
                return LongLastingElement<T>() as T
            }
        }

        fun <T> getInstance(owner: ViewModelStoreOwner): LongLastingElement<T> {
            val viewModelProvider = ViewModelProvider(owner.viewModelStore, LongLastingElementFactory())
            return viewModelProvider.get(LongLastingElement::class.java as Class<LongLastingElement<T>>)
        }
    }
}