DataBindingDelegates.kt

package io.github.yaraki.miscex

import android.view.ViewGroup
import androidx.databinding.DataBindingUtil
import androidx.databinding.ViewDataBinding
import androidx.fragment.app.Fragment
import androidx.fragment.app.FragmentActivity
import androidx.lifecycle.Lifecycle
import androidx.lifecycle.LifecycleEventObserver

/**
 * Retrieves a data binding handle in an Activity.
 *
 * ```
 *     private val binding: MainActivityBinding by dataBindings()
 * ```
 */
inline fun <reified BindingT : ViewDataBinding> FragmentActivity.dataBindings() =
    object : Lazy<BindingT> {

        private var cached: BindingT? = null

        override val value: BindingT
            get() = cached ?: DataBindingUtil.bind<BindingT>(
                findViewById<ViewGroup>(android.R.id.content).getChildAt(0)
            )!!.also { cached = it }

        override fun isInitialized() = cached != null
    }

/**
 * Retrieves a data binding handle in a Fragment. The returned instance is already set up with the
 * [androidx.lifecycle.LifecycleOwner]. The field is available only after [Fragment.onViewCreated].
 *
 * ```
 *     private val binding: HomeFragmentBinding by dataBindings()
 *
 *     override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
 *         binding.someVariable = ...
 *     }
 * ```
 */
inline fun <reified BindingT : ViewDataBinding> Fragment.dataBindings() = object : Lazy<BindingT> {

    private var cached: BindingT? = null

    private val observer = LifecycleEventObserver { _, event ->
        if (event == Lifecycle.Event.ON_DESTROY) {
            cached = null
        }
    }

    override val value: BindingT
        get() = cached ?: DataBindingUtil.bind<BindingT>(requireView())!!.also {
            viewLifecycleOwner.lifecycle.addObserver(observer)
            it.lifecycleOwner = viewLifecycleOwner
            cached = it
        }

    override fun isInitialized() = cached != null
}