Simplify and reduce overhead of lazy view binding in Fragments (#4269)

This reduces complexity of view binding inflation in Fragments, and also
reduces overhead (no `KProperty` objects need to be generated by the
compiler) by implementing `Lazy` instead of `ReadOnlyProperty`.

For a full explanation, see this [detailed blog
post](https://medium.com/@bladecoder/viewlifecyclelazy-and-other-ways-to-avoid-view-memory-leaks-in-android-fragments-4aa982e6e579).

app/src/main/java/com/keylesspalace/tusky/util/ViewBindingExtensions.kt

@@ -4,16 +4,14 @@ import android.view.LayoutInflater
 import android.view.View
 import androidx.appcompat.app.AppCompatActivity
 import androidx.fragment.app.Fragment
-import androidx.lifecycle.DefaultLifecycleObserver
 import androidx.lifecycle.Lifecycle
+import androidx.lifecycle.LifecycleEventObserver
 import androidx.lifecycle.LifecycleOwner
-import androidx.lifecycle.Observer
 import androidx.viewbinding.ViewBinding
-import kotlin.properties.ReadOnlyProperty
-import kotlin.reflect.KProperty
 
 /**
- * https://medium.com/@Zhuinden/simple-one-liner-viewbinding-in-fragments-and-activities-with-kotlin-961430c6c07c
+ * Original code: https://medium.com/@Zhuinden/simple-one-liner-viewbinding-in-fragments-and-activities-with-kotlin-961430c6c07c
+ * Refactor: https://bladecoder.medium.com/viewlifecyclelazy-and-other-ways-to-avoid-view-memory-leaks-in-android-fragments-4aa982e6e579
  */
 
 inline fun <T : ViewBinding> AppCompatActivity.viewBinding(
@@ -22,55 +20,32 @@ inline fun <T : ViewBinding> AppCompatActivity.viewBinding(
     bindingInflater(layoutInflater)
 }
 
-class FragmentViewBindingDelegate<T : ViewBinding>(
-    val fragment: Fragment,
-    val viewBindingFactory: (View) -> T
-) : ReadOnlyProperty<Fragment, T> {
-    private var binding: T? = null
+private class ViewLifecycleLazy<out T : Any>(
+    private val fragment: Fragment,
+    private val initializer: (View) -> T
+) : Lazy<T>, LifecycleEventObserver {
+    private var cached: T? = null
 
-    init {
-        fragment.lifecycle.addObserver(object : DefaultLifecycleObserver {
-            val viewLifecycleOwnerLiveDataObserver =
-                Observer<LifecycleOwner?> {
-                    val viewLifecycleOwner = it ?: return@Observer
-
-                    viewLifecycleOwner.lifecycle.addObserver(object : DefaultLifecycleObserver {
-                        override fun onDestroy(owner: LifecycleOwner) {
-                            binding = null
+    override val value: T
+        get() {
+            return cached ?: run {
+                val newValue = initializer(fragment.requireView())
+                cached = newValue
+                fragment.viewLifecycleOwner.lifecycle.addObserver(this)
+                newValue
             }
-                    })
         }
 
-            override fun onCreate(owner: LifecycleOwner) {
-                fragment.viewLifecycleOwnerLiveData.observeForever(
-                    viewLifecycleOwnerLiveDataObserver
-                )
-            }
+    override fun isInitialized() = cached != null
 
-            override fun onDestroy(owner: LifecycleOwner) {
-                fragment.viewLifecycleOwnerLiveData.removeObserver(
-                    viewLifecycleOwnerLiveDataObserver
-                )
-            }
-        })
-    }
+    override fun toString() = cached.toString()
 
-    override fun getValue(thisRef: Fragment, property: KProperty<*>): T {
-        val binding = binding
-        if (binding != null) {
-            return binding
+    override fun onStateChanged(source: LifecycleOwner, event: Lifecycle.Event) {
+        if (event == Lifecycle.Event.ON_DESTROY) {
+            cached = null
         }
-
-        val lifecycle = fragment.viewLifecycleOwner.lifecycle
-        if (!lifecycle.currentState.isAtLeast(Lifecycle.State.INITIALIZED)) {
-            throw IllegalStateException(
-                "Should not attempt to get bindings when Fragment views are destroyed."
-            )
-        }
-
-        return viewBindingFactory(thisRef.requireView()).also { this.binding = it }
     }
 }
 
-fun <T : ViewBinding> Fragment.viewBinding(viewBindingFactory: (View) -> T) =
-    FragmentViewBindingDelegate(this, viewBindingFactory)
+fun <T : ViewBinding> Fragment.viewBinding(viewBindingFactory: (View) -> T): Lazy<T> =
+    ViewLifecycleLazy(this, viewBindingFactory)