ViewBinding delegates

ViewBindingDelegate.kt

@file:Suppress("unused")

import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import androidx.appcompat.app.AppCompatActivity
import androidx.fragment.app.DialogFragment
import androidx.fragment.app.Fragment
import androidx.lifecycle.DefaultLifecycleObserver
import androidx.lifecycle.Lifecycle
import androidx.lifecycle.LifecycleOwner
import androidx.lifecycle.Observer
import androidx.viewbinding.ViewBinding
import kotlin.properties.ReadOnlyProperty
import kotlin.reflect.KProperty

/** Activity binding delegate, may be used since onCreate up to onDestroy (inclusive) */
inline fun <T : ViewBinding> AppCompatActivity.viewBinding(
    crossinline factory: (LayoutInflater) -> T,
) = lazy(LazyThreadSafetyMode.NONE) {
    factory(layoutInflater)
}

/** Fragment binding delegate, may be used since onViewCreated up to onDestroyView (inclusive) */
inline fun <T : ViewBinding> Fragment.viewBinding(
    crossinline factory: (View) -> T,
): ReadOnlyProperty<Fragment, T> = object : ReadOnlyProperty<Fragment, T>, DefaultLifecycleObserver {

    private var binding: T? = null

    private val viewLifecycleOwnerLiveDataObserver = Observer<LifecycleOwner?> {
        it?.lifecycle?.addObserver(object : DefaultLifecycleObserver {
            override fun onDestroy(owner: LifecycleOwner) {
                binding = null
            }
        })
    }

    init {
        lifecycle.addObserver(this)
    }

    override fun getValue(thisRef: Fragment, property: KProperty<*>): T {
        val capturedBinding = binding
        if (capturedBinding != null) {
            return capturedBinding
        }

        if (!viewLifecycleOwner.lifecycle.currentState.isAtLeast(Lifecycle.State.INITIALIZED)) {
            throw IllegalStateException("Should not attempt to get bindings when Fragment views are destroyed.")
        }

        return factory(thisRef.requireView()).also { this.binding = it }
    }

    override fun onCreate(owner: LifecycleOwner) {
        viewLifecycleOwnerLiveData.observeForever(viewLifecycleOwnerLiveDataObserver)
    }

    override fun onDestroy(owner: LifecycleOwner) {
        viewLifecycleOwnerLiveData.removeObserver(viewLifecycleOwnerLiveDataObserver)
    }
}

/** Binding delegate for DialogFragments implementing onCreateDialog (like Activities, they don't
 *  have a separate view lifecycle), may be used since onCreateDialog up to onDestroy (inclusive) */
inline fun <T : ViewBinding> DialogFragment.viewBinding(
    crossinline factory: (LayoutInflater) -> T,
) = lazy(LazyThreadSafetyMode.NONE) {
    factory(layoutInflater)
}

/** Not really a delegate, just a small helper for RecyclerView.ViewHolders */
inline fun <T : ViewBinding> ViewGroup.viewBinding(
    factory: (LayoutInflater, ViewGroup, Boolean) -> T,
) = factory(LayoutInflater.from(context), this, false)