main: add proper backwards navigation

Move the backwards navigation hook from DetailFragment to MainFragment
and modify it so that it collapses the playback panel when one navs
back.

app/src/main/java/org/oxycblt/auxio/MainFragment.kt

@@ -24,10 +24,13 @@ import android.view.LayoutInflater
 import android.view.View
 import android.view.ViewGroup
 import android.widget.Button
+import androidx.activity.OnBackPressedCallback
 import androidx.activity.result.contract.ActivityResultContracts
 import androidx.core.content.res.ResourcesCompat
 import androidx.fragment.app.Fragment
 import androidx.fragment.app.activityViewModels
+import androidx.navigation.findNavController
+import androidx.navigation.fragment.findNavController
 import com.google.android.material.snackbar.Snackbar
 import org.oxycblt.auxio.databinding.FragmentMainBinding
 import org.oxycblt.auxio.detail.DetailViewModel
@@ -41,12 +44,12 @@ import org.oxycblt.auxio.util.logD
  * A wrapper around the home fragment that shows the playback fragment and controls
  * the more high-level navigation features.
  * @author OxygenCobalt
- * TODO: Handle backnav with playback view
  */
 class MainFragment : Fragment(), PlaybackLayout.ActionCallback {
     private val playbackModel: PlaybackViewModel by activityViewModels()
     private val detailModel: DetailViewModel by activityViewModels()
     private val musicModel: MusicViewModel by activityViewModels()
+    private var callback: Callback? = null
 
     override fun onCreateView(
         inflater: LayoutInflater,
@@ -66,24 +69,31 @@ class MainFragment : Fragment(), PlaybackLayout.ActionCallback {
 
         binding.lifecycleOwner = viewLifecycleOwner
 
+        requireActivity().onBackPressedDispatcher.addCallback(
+            viewLifecycleOwner,
+            Callback(binding).also {
+                callback = it
+            }
+        )
+
         // --- VIEWMODEL SETUP ---
 
-        binding.mainBarLayout.setActionCallback(this)
+        binding.playbackLayout.setActionCallback(this)
 
-        binding.mainBarLayout.setSong(playbackModel.song.value)
-        binding.mainBarLayout.setPlaying(playbackModel.isPlaying.value!!)
-        binding.mainBarLayout.setPosition(playbackModel.position.value!!)
+        binding.playbackLayout.setSong(playbackModel.song.value)
+        binding.playbackLayout.setPlaying(playbackModel.isPlaying.value!!)
+        binding.playbackLayout.setPosition(playbackModel.position.value!!)
 
         playbackModel.song.observe(viewLifecycleOwner) { song ->
-            binding.mainBarLayout.setSong(song)
+            binding.playbackLayout.setSong(song)
         }
 
         playbackModel.isPlaying.observe(viewLifecycleOwner) { isPlaying ->
-            binding.mainBarLayout.setPlaying(isPlaying)
+            binding.playbackLayout.setPlaying(isPlaying)
         }
 
         playbackModel.position.observe(viewLifecycleOwner) { pos ->
-            binding.mainBarLayout.setPosition(pos)
+            binding.playbackLayout.setPosition(pos)
         }
 
         // Initialize music loading. Do it here so that it shows on every fragment that this
@@ -144,6 +154,23 @@ class MainFragment : Fragment(), PlaybackLayout.ActionCallback {
         return binding.root
     }
 
+    override fun onResume() {
+        super.onResume()
+        callback?.isEnabled = true
+    }
+
+    override fun onPause() {
+        super.onPause()
+        callback?.isEnabled = false
+    }
+
+    override fun onDestroyView() {
+        super.onDestroyView()
+
+        // This callback has access to the binding, so make sure we clear it when we're done.
+        callback = null
+    }
+
     override fun onNavToItem() {
         detailModel.navToItem(playbackModel.song.value ?: return)
     }
@@ -159,4 +186,24 @@ class MainFragment : Fragment(), PlaybackLayout.ActionCallback {
     override fun onNext() {
         playbackModel.skipNext()
     }
+
+    /**
+     * A back press callback that handles how to respond to backwards navigation in the detail
+     * fragments and the playback panel.
+     */
+    inner class Callback(private val binding: FragmentMainBinding) : OnBackPressedCallback(false) {
+        override fun handleOnBackPressed() {
+            if (!binding.playbackLayout.collapse()) {
+                val navController = binding.exploreNavHost.findNavController()
+
+                if (navController.currentDestination?.id == navController.graph.startDestination) {
+                    isEnabled = false
+                    requireActivity().onBackPressed()
+                    isEnabled = true
+                } else {
+                    navController.navigateUp()
+                }
+            }
+        }
+    }
 }

app/src/main/java/org/oxycblt/auxio/detail/DetailFragment.kt

@@ -18,9 +18,6 @@
 
 package org.oxycblt.auxio.detail
 
-import android.os.Bundle
-import android.view.View
-import androidx.activity.OnBackPressedCallback
 import androidx.annotation.MenuRes
 import androidx.appcompat.widget.PopupMenu
 import androidx.core.view.forEach
@@ -44,22 +41,12 @@ abstract class DetailFragment : Fragment() {
     protected val playbackModel: PlaybackViewModel by activityViewModels()
     protected val binding by memberBinding(FragmentDetailBinding::inflate)
 
-    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
-        requireActivity().onBackPressedDispatcher.addCallback(viewLifecycleOwner, callback)
-    }
-
     override fun onResume() {
         super.onResume()
 
-        callback.isEnabled = true
         detailModel.setNavigating(false)
     }
 
-    override fun onPause() {
-        super.onPause()
-        callback.isEnabled = false
-    }
-
     override fun onStop() {
         super.onStop()
 
@@ -149,21 +136,4 @@ abstract class DetailFragment : Fragment() {
             show()
         }
     }
-
-    // Override the back button so that going back will only exit the detail fragments instead of
-    // the entire app.
-    private val callback = object : OnBackPressedCallback(false) {
-
-        override fun handleOnBackPressed() {
-            val navController = findNavController()
-            // Check if it's the root of nested fragments in this NavHost
-            if (navController.currentDestination?.id == navController.graph.startDestination) {
-                isEnabled = false
-                requireActivity().onBackPressed()
-                isEnabled = true
-            } else {
-                navController.navigateUp()
-            }
-        }
-    }
 }

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

@@ -23,6 +23,7 @@ import com.google.android.material.shape.MaterialShapeDrawable
 import org.oxycblt.auxio.BuildConfig
 import org.oxycblt.auxio.R
 import org.oxycblt.auxio.music.Song
+import org.oxycblt.auxio.util.logD
 import org.oxycblt.auxio.util.resolveAttr
 import org.oxycblt.auxio.util.systemBarsCompat
 import kotlin.math.abs
@@ -198,11 +199,17 @@ class PlaybackLayout @JvmOverloads constructor(
 
     /**
      * Collapse the panel if it is currently expanded.
+     * @return If the panel was collapsed or not.
      */
-    fun collapse() {
+    fun collapse(): Boolean {
+        logD(panelState)
         if (panelState == PanelState.EXPANDED) {
             applyState(PanelState.COLLAPSED)
+            logD("I AM EXPANDED WILL COLLAPSE")
+            return true
         }
+
+        return false
     }
 
     private fun applyState(state: PanelState) {

app/src/main/res/layout/fragment_main.xml

@@ -5,10 +5,9 @@
     tools:context=".MainFragment">
 
     <org.oxycblt.auxio.playback.PlaybackLayout
-        android:id="@+id/main_bar_layout"
+        android:id="@+id/playback_layout"
         android:layout_width="match_parent"
-        android:layout_height="match_parent"
-        android:orientation="vertical">
+        android:layout_height="match_parent">
 
         <androidx.fragment.app.FragmentContainerView
             android:id="@+id/explore_nav_host"

app/src/main/res/navigation/nav_main.xml

@@ -18,17 +18,17 @@
         <action
             android:id="@+id/action_show_settings"
             app:destination="@id/settings_fragment"
-            app:enterAnim="@anim/anim_nav_slide_up"
-            app:exitAnim="@anim/anim_stationary"
-            app:popEnterAnim="@anim/anim_stationary"
-            app:popExitAnim="@anim/anim_nav_slide_down" />
+            app:enterAnim="@anim/nav_default_enter_anim"
+            app:exitAnim="@anim/nav_default_exit_anim"
+            app:popEnterAnim="@anim/nav_default_pop_enter_anim"
+            app:popExitAnim="@anim/nav_default_pop_exit_anim" />
         <action
             android:id="@+id/action_show_about"
             app:destination="@id/about_fragment"
-            app:enterAnim="@anim/anim_nav_slide_up"
-            app:exitAnim="@anim/anim_stationary"
-            app:popEnterAnim="@anim/anim_stationary"
-            app:popExitAnim="@anim/anim_nav_slide_down" />
+            app:enterAnim="@anim/nav_default_enter_anim"
+            app:exitAnim="@anim/nav_default_exit_anim"
+            app:popEnterAnim="@anim/nav_default_pop_enter_anim"
+            app:popExitAnim="@anim/nav_default_pop_exit_anim" />
     </fragment>
 
     <fragment