Allow fragments to use member variable bindings

Create a binder delegate so that some fragments can use a binding as a member variable without nullability issues or memory leaks.

app/src/main/java/org/oxycblt/auxio/playback/CompactPlaybackFragment.kt

@@ -5,7 +5,6 @@ import android.os.Bundle
 import android.view.LayoutInflater
 import android.view.View
 import android.view.ViewGroup
-import android.widget.ImageButton
 import androidx.core.content.ContextCompat
 import androidx.fragment.app.Fragment
 import androidx.fragment.app.activityViewModels
@@ -15,6 +14,7 @@ import org.oxycblt.auxio.R
 import org.oxycblt.auxio.databinding.FragmentCompactPlaybackBinding
 import org.oxycblt.auxio.logD
 import org.oxycblt.auxio.music.MusicStore
+import org.oxycblt.auxio.ui.memberBinding
 import org.oxycblt.auxio.ui.isLandscape
 
 /**
@@ -26,14 +26,15 @@ import org.oxycblt.auxio.ui.isLandscape
  */
 class CompactPlaybackFragment : Fragment() {
     private val playbackModel: PlaybackViewModel by activityViewModels()
+    private val binding: FragmentCompactPlaybackBinding by memberBinding(
+        FragmentCompactPlaybackBinding::inflate
+    )
 
     override fun onCreateView(
         inflater: LayoutInflater,
         container: ViewGroup?,
         savedInstanceState: Bundle?
     ): View {
-        val binding = FragmentCompactPlaybackBinding.inflate(inflater)
-
         val isLandscape = isLandscape(resources)
 
         // --- UI SETUP ---
@@ -94,7 +95,7 @@ class CompactPlaybackFragment : Fragment() {
 
         // Use the caveman method of getting a view as storing the binding will cause a memory
         // leak.
-        val playbackControls = requireView().findViewById<ImageButton>(R.id.playback_controls)
+        val playbackControls = binding.playbackControls
 
         val iconPauseToPlay = ContextCompat.getDrawable(
             requireContext(), R.drawable.ic_pause_to_play

app/src/main/java/org/oxycblt/auxio/playback/PlaybackFragment.kt

@@ -8,7 +8,6 @@ import android.view.MenuItem
 import android.view.View
 import android.view.ViewGroup
 import android.widget.SeekBar
-import android.widget.TextView
 import androidx.core.content.ContextCompat
 import androidx.fragment.app.Fragment
 import androidx.fragment.app.activityViewModels
@@ -18,6 +17,7 @@ import org.oxycblt.auxio.databinding.FragmentPlaybackBinding
 import org.oxycblt.auxio.logD
 import org.oxycblt.auxio.playback.state.LoopMode
 import org.oxycblt.auxio.ui.accent
+import org.oxycblt.auxio.ui.memberBinding
 import org.oxycblt.auxio.ui.toColor
 
 /**
@@ -28,14 +28,13 @@ import org.oxycblt.auxio.ui.toColor
  */
 class PlaybackFragment : Fragment(), SeekBar.OnSeekBarChangeListener {
     private val playbackModel: PlaybackViewModel by activityViewModels()
+    private val binding: FragmentPlaybackBinding by memberBinding(FragmentPlaybackBinding::inflate)
 
     override fun onCreateView(
         inflater: LayoutInflater,
         container: ViewGroup?,
         savedInstanceState: Bundle?
     ): View {
-        val binding = FragmentPlaybackBinding.inflate(inflater)
-
         // TODO: Add a swipe-to-next-track function using a ViewPager
 
         // Create accents & icons to use
@@ -203,8 +202,7 @@ class PlaybackFragment : Fragment(), SeekBar.OnSeekBarChangeListener {
     override fun onStop() {
         super.onStop()
 
-        // Stop the marqueeing of the song name to prevent a weird memory leak
+        binding.playbackSong.isSelected = false
-        requireView().findViewById<TextView>(R.id.playback_song).isSelected = false
     }
 
     // Seeking callbacks

app/src/main/java/org/oxycblt/auxio/ui/FragmentBinderDelegate.kt

@@ -0,0 +1,81 @@
+package org.oxycblt.auxio.ui
+
+import android.os.Looper
+import android.view.LayoutInflater
+import androidx.fragment.app.Fragment
+import androidx.lifecycle.DefaultLifecycleObserver
+import androidx.lifecycle.Lifecycle
+import androidx.lifecycle.LifecycleObserver
+import androidx.lifecycle.LifecycleOwner
+import androidx.lifecycle.OnLifecycleEvent
+import androidx.viewbinding.ViewBinding
+import java.lang.IllegalStateException
+import kotlin.properties.ReadOnlyProperty
+import kotlin.reflect.KProperty
+
+/**
+ * A delegate that creates a binding that can be used as a member variable without nullability or
+ * memory leaks.
+ */
+fun <T : ViewBinding> Fragment.memberBinding(
+    viewBindingFactory: (LayoutInflater) -> T,
+    disposeEvents: T.() -> Unit = {}
+) = FragmentBinderDelegate(this, viewBindingFactory, disposeEvents)
+
+/**
+ * The delegate for the [binder] shortcut function.
+ * Adapted from KAHelpers (https://github.com/FunkyMuse/KAHelpers/tree/master/viewbinding)
+ */
+class FragmentBinderDelegate<T : ViewBinding>(
+    private val fragment: Fragment,
+    private val binder: (LayoutInflater) -> T,
+    private val disposeEvents: T.() -> Unit
+) : ReadOnlyProperty<Fragment, T>, LifecycleObserver {
+    private var fragmentBinding: T? = null
+
+    init {
+        fragment.observeOwnerThroughCreation {
+            lifecycle.addObserver(this@FragmentBinderDelegate)
+        }
+    }
+
+    private inline fun Fragment.observeOwnerThroughCreation(
+        crossinline viewOwner: LifecycleOwner.() -> Unit
+    ) {
+        lifecycle.addObserver(object : DefaultLifecycleObserver {
+            override fun onCreate(owner: LifecycleOwner) {
+                super.onCreate(owner)
+
+                viewLifecycleOwnerLiveData.observe(this@observeOwnerThroughCreation) { owner ->
+                    owner.viewOwner()
+                }
+            }
+        })
+    }
+
+    override fun getValue(thisRef: Fragment, property: KProperty<*>): T {
+        if (Looper.myLooper() != Looper.getMainLooper()) {
+            throw IllegalThreadStateException("View can only be accessed on the main thread.")
+        }
+
+        val binding = fragmentBinding
+        if (binding != null) {
+            return binding
+        }
+
+        val lifecycle = fragment.viewLifecycleOwner.lifecycle
+
+        if (!lifecycle.currentState.isAtLeast(Lifecycle.State.INITIALIZED)) {
+            throw IllegalStateException("Fragment views are destroyed.")
+        }
+
+        return binder(LayoutInflater.from(thisRef.requireContext())).also { fragmentBinding = it }
+    }
+
+    @Suppress("UNUSED")
+    @OnLifecycleEvent(Lifecycle.Event.ON_DESTROY)
+    fun dispose() {
+        fragmentBinding?.disposeEvents()
+        fragmentBinding = null
+    }
+}