Lazy ViewBinding delegate designed to imitate `androidx.fragment.app.viewModels`.

ViewBindingLazy.kt

/*
Copyright 2021 Felix Zedén Yverås

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated
documentation files (the "Software"), to deal in the Software without restriction, including without limitation the
rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit
persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the
Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE
WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*/

package se.fzy.snippets

import android.view.View
import androidx.annotation.IdRes
import androidx.core.view.ViewCompat
import androidx.fragment.app.Fragment
import androidx.lifecycle.Lifecycle
import androidx.lifecycle.LifecycleObserver
import androidx.lifecycle.OnLifecycleEvent
import androidx.viewbinding.ViewBinding

class ViewBindingLazy<VB : ViewBinding>(
        private val viewBindingClass: Class<VB>,
        private val viewLifecycleProvider: () -> Lifecycle,
        private val rootViewProvider: () -> View,
) : Lazy<VB>, LifecycleObserver {
    private var cached: VB? = null

    override val value: VB
        get() {
            if (cached == null) {
                viewLifecycleProvider().addObserver(this)
                // Use java reflection to avoid a dependency on kotlin-reflect.jar
                @Suppress("UNCHECKED_CAST")
                cached = viewBindingClass
                        .getMethod("bind", View::class.java)
                        .invoke(null, rootViewProvider()) as VB
            }
            return cached!!
        }

    override fun isInitialized(): Boolean = cached != null

    @Suppress("unused")
    @OnLifecycleEvent(Lifecycle.Event.ON_DESTROY)
    fun onDestroy() {
        cached = null
    }
}

/**
 * Convenience method for retrieving view bindings designed to imitate
 * [androidx.fragment.app.viewModels].
 *
 * **Basic usage:**
 * ```kotlin
 * private lateinit var views: MyFragmentBindings by viewBindings()
 * ```
 *
 * **See also:**
 * [https://developer.android.com/topic/libraries/view-binding](https://developer.android.com/topic/libraries/view-binding)
 *
 * @param rootViewProvider function providing the view on which to call `VB.bind(view)`
 */
inline fun <reified VB : ViewBinding> Fragment.viewBindings(
        noinline rootViewProvider: () -> View = { requireView() },
): Lazy<VB> = ViewBindingLazy(
        VB::class.java,
        { viewLifecycleOwner.lifecycle },
        rootViewProvider,
)

/**
 * @see Fragment.viewBindings
 */
inline fun <reified VB : ViewBinding> Fragment.viewBindings(
        @IdRes rootView: Int,
): Lazy<VB> = ViewBindingLazy(
        VB::class.java,
        { viewLifecycleOwner.lifecycle },
        { ViewCompat.requireViewById(requireView(), rootView) }
)