View Binding Holder for Fragments

view-binding-holder.txt

import android.view.View
import androidx.viewbinding.ViewBinding

/**
 * Creates a [ViewBindingHolder] with the given [ViewBinding] factory to
 * act as an accessor to the [ViewBinding].
 *
 * ```
 * class MyFragment : Fragment(R.layout.fragment_mine) {
 *
 *     private val binding = viewBindingFrom(FragmentMineBinding::bind)
 *     private var counter: Int = 0
 *
 *     override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
 *         super.onViewCreated(view, savedInstanceState)
 *         binding.bindTo(view)
 *         binding.views.buttonIncrement.setOnClickListener {
 *              counter += 1
 *              updateCounterDisplay()
 *         }
 *     }
 *
 *     override fun onDestroyView() {
 *         super.onDestroyView()
 *         binding.clear()
 *     }
 *
 *     private fun updateCounterDisplay() {
 *         binding.doWithViews {
 *             textCounter.setText("Counter: $counter")
 *         }
 *     }
 * ```
 */
fun <T : ViewBinding> viewBindingFrom(factory: (View) -> T): ViewBindingHolder<T> {
    return ViewBindingHolder(factory)
}

/**
 * Wrapper around a [ViewBinding] intended to slightly reduce boiler plate
 * when [ViewBinding]s are used in Fragments.
 */
class ViewBindingHolder<T : ViewBinding>(
    private val factory: (View) -> T
) {

    private var viewBinding: T? = null

    /**
     * Gets the view binding instance that has been bound to this holder instance.
     */
    val views: T
        get() = requireNotNull(viewBinding) { "The associated view binding does not exist." }

    /**
     * Executes the block provided with the view binding instance if it exists.
     */
    fun doWithViews(block: T.() -> Unit) {
        viewBinding?.let(block)
    }

    /**
     * Binds a view binding instance from the View provided and returns the View
     * as a convenience.
     */
    fun bindTo(view: View): View {
        viewBinding = factory.invoke(view)
        return view
    }

    /**
     * Frees the view binding instance so it and its associated views
     * are not leaked.
     */
    fun clear() {
        viewBinding = null
    }
}