software-mansion · WoLewicki · Sep 23, 2021 · Sep 22, 2021
diff --git a/android/src/main/java/com/swmansion/rnscreens/ScreenStack.kt b/android/src/main/java/com/swmansion/rnscreens/ScreenStack.kt
@@ -3,8 +3,6 @@ package com.swmansion.rnscreens
 import android.content.Context
 import android.graphics.Canvas
 import android.view.View
-import androidx.fragment.app.Fragment
-import androidx.fragment.app.FragmentManager
 import androidx.fragment.app.FragmentTransaction
 import com.facebook.react.bridge.ReactContext
 import com.facebook.react.uimanager.UIManagerModule
@@ -20,21 +18,6 @@ class ScreenStack(context: Context?) : ScreenContainer<ScreenStackFragment>(cont
     private val drawingOpPool: MutableList<DrawingOp> = ArrayList()
     private val drawingOps: MutableList<DrawingOp> = ArrayList()
     private var mTopScreen: ScreenStackFragment? = null
-    private val mBackStackListener = FragmentManager.OnBackStackChangedListener {
-        if (mFragmentManager?.backStackEntryCount == 0) {
-            // when back stack entry count hits 0 it means the user's navigated back using hw back
-            // button. As the "fake" transaction we installed on the back stack does nothing we need
-            // to handle back navigation on our own.
-            mTopScreen?.let { dismiss(it) }
-        }
-    }
-    private val mLifecycleCallbacks: FragmentManager.FragmentLifecycleCallbacks = object : FragmentManager.FragmentLifecycleCallbacks() {
-        override fun onFragmentResumed(fm: FragmentManager, f: Fragment) {
-            if (mTopScreen === f) {
-                setupBackHandlerIfNeeded(f)
-            }
-        }
-    }
     private var mRemovalTransitionStarted = false
     private var isDetachingCurrentScreen = false
     private var reverseLastTwoChildren = false
@@ -65,28 +48,6 @@ class ScreenStack(context: Context?) : ScreenContainer<ScreenStackFragment>(cont
         return ScreenStackFragment(screen)
     }
 
-    override fun onDetachedFromWindow() {
-        mFragmentManager?.let {
-            it.removeOnBackStackChangedListener(mBackStackListener)
-            it.unregisterFragmentLifecycleCallbacks(mLifecycleCallbacks)
-            if (!it.isStateSaved && !it.isDestroyed) {
-                // State save means that the container where fragment manager was installed has been
-                // unmounted.
-                // This could happen as a result of dismissing nested stack. In such a case we don't need to
-                // reset back stack as it'd result in a crash caused by the fact the fragment manager is no
-                // longer attached.
-                it.popBackStack(BACK_STACK_TAG, FragmentManager.POP_BACK_STACK_INCLUSIVE)
-            }
-        }
-        super.onDetachedFromWindow()
-    }
-
-    override fun onAttachedToWindow() {
-        super.onAttachedToWindow()
-        val fragmentManager = requireNotNull(mFragmentManager, { "mFragmentManager is null when ScreenStack attached to window" })
-        fragmentManager.registerFragmentLifecycleCallbacks(mLifecycleCallbacks, false)
-    }
-
     override fun startViewTransition(view: View) {
         super.startViewTransition(view)
         mRemovalTransitionStarted = true
@@ -278,7 +239,6 @@ class ScreenStack(context: Context?) : ScreenContainer<ScreenStackFragment>(cont
             mStack.clear()
             mStack.addAll(mScreenFragments)
             it.commitNowAllowingStateLoss()
-            mTopScreen?.let { screen -> setupBackHandlerIfNeeded(screen) }
         }
     }
 
@@ -288,61 +248,6 @@ class ScreenStack(context: Context?) : ScreenContainer<ScreenStackFragment>(cont
         }
     }
 
-    /**
-     * The below method sets up fragment manager's back stack in a way that it'd trigger our back
-     * stack change listener when hw back button is clicked.
-     *
-     *
-     * Because back stack by default rolls back the transaction the stack entry is associated with
-     * we generate a "fake" transaction that hides and shows the top fragment. As a result when back
-     * stack entry is rolled back nothing happens and we are free to handle back navigation on our own
-     * in `mBackStackListener`.
-     *
-     *
-     * We pop that "fake" transaction each time we update stack and we add a new one in case the
-     * top screen is allowed to be dismissed using hw back button. This way in the listener we can
-     * tell if back button was pressed based on the count of the items on back stack. We expect 0
-     * items in case hw back is pressed because we try to keep the number of items at 1 by always
-     * resetting and adding new items. In case we don't add a new item to back stack we remove
-     * listener so that it does not get triggered.
-     *
-     *
-     * It is important that we don't install back handler when stack contains a single screen as in
-     * that case we want the parent navigator or activity handler to take over.
-     */
-    private fun setupBackHandlerIfNeeded(topScreen: ScreenStackFragment) {
-        if (mTopScreen?.isResumed != true) {
-            // if the top fragment is not in a resumed state, adding back stack transaction would throw.
-            // In such a case we skip installing back handler and use FragmentLifecycleCallbacks to get
-            // notified when it gets resumed so that we can install the handler.
-            return
-        }
-        mFragmentManager?.let {
-            it.removeOnBackStackChangedListener(mBackStackListener)
-            it.popBackStack(BACK_STACK_TAG, FragmentManager.POP_BACK_STACK_INCLUSIVE)
-            var firstScreen: ScreenStackFragment? = null
-            var i = 0
-            val size = mStack.size
-            while (i < size) {
-                val screen = mStack[i]
-                if (!mDismissed.contains(screen)) {
-                    firstScreen = screen
-                    break
-                }
-                i++
-            }
-            if (topScreen !== firstScreen && topScreen.isDismissible) {
-                it
-                    .beginTransaction()
-                    .show(topScreen)
-                    .addToBackStack(BACK_STACK_TAG)
-                    .setPrimaryNavigationFragment(topScreen)
-                    .commitNowAllowingStateLoss()
-                it.addOnBackStackChangedListener(mBackStackListener)
-            }
-        }
-    }
-
     // below methods are taken from
     // https://github.com/airbnb/native-navigation/blob/9cf50bf9b751b40778f473f3b19fcfe2c4d40599/lib/android/src/main/java/com/airbnb/android/react/navigation/ScreenCoordinatorLayout.java#L43
     // and are used to swap the order of drawing views when navigating forward with the transitions
@@ -418,7 +323,6 @@ class ScreenStack(context: Context?) : ScreenContainer<ScreenStackFragment>(cont
     }
 
     companion object {
-        private const val BACK_STACK_TAG = "RN_SCREEN_LAST"
         private fun isSystemAnimation(stackAnimation: StackAnimation): Boolean {
             return stackAnimation === StackAnimation.DEFAULT || stackAnimation === StackAnimation.FADE || stackAnimation === StackAnimation.NONE
         }

diff --git a/android/src/main/java/com/swmansion/rnscreens/ScreenStackFragment.kt b/android/src/main/java/com/swmansion/rnscreens/ScreenStackFragment.kt
@@ -145,9 +145,6 @@ class ScreenStackFragment : ScreenFragment {
         return view
     }
 
-    val isDismissible: Boolean
-        get() = screen.isGestureEnabled
-
     fun canNavigateBack(): Boolean {
         val container: ScreenContainer<*>? = screen.container
         check(container is ScreenStack) { "ScreenStackFragment added into a non-stack container" }

diff --git a/guides/GUIDE_FOR_LIBRARY_AUTHORS.md b/guides/GUIDE_FOR_LIBRARY_AUTHORS.md
@@ -412,3 +412,7 @@ Check [LifecycleAwareView.java](https://github.com/kmagiera/react-native-screens
 In addition to that, you will need to register for receiving these updates. This can be done using [`LifecycleHelper.register`](https://github.com/kmagiera/react-native-screens/blob/master/android/src/main/java/com/swmansion/rnscreens/LifecycleHelper.java#L50).
 Remember to call [`LifecycleHelper.unregister`](https://github.com/kmagiera/react-native-screens/blob/master/android/src/main/java/com/swmansion/rnscreens/LifecycleHelper.java#L59) before the view is dropped.
 Please refer to [SampleLifecycleAwareViewManager.java](https://github.com/kmagiera/react-native-screens/blob/master/Example/android/app/src/main/java/com/swmansion/rnscreens/example/SampleLifecycleAwareViewManager.java) from our example app to see what are the best ways of using the above methods.
+
+## Android hardware back button
+
+In order to properly handle the hardware back button on Android, you should implement the navigation logic concerning it. You can see an example of how it is done in `react-navigation` here: https://github.com/react-navigation/react-navigation/blob/6cba517b74f5fd092db21d5574b558ef2d80897b/packages/native/src/useBackButton.tsx.