From 06b928f5c1a39e8e7b96bb360e4ac425a4c1638d Mon Sep 17 00:00:00 2001
From: Krzysztof Magiera <krzys@swmansion.com>
Date: Wed, 5 Feb 2020 16:22:10 +0100
Subject: [PATCH] Fix showing sw back button on nested stack on Android. (#308)

This change fixes a problem with native stack on Android where we'd display a sw back button on screens that are nested stack navigatodespite the fact those screens were the initial screens in the whole container stack. In #306 we introuced a change that would allow for displaying sw back in nested stacks, however that change did not handle the case where screen is a root screen of a container that is nested and placed as an initial screen in another container.
---
 .../rnscreens/ScreenStackFragment.java        | 21 +++++++++++++++++++
 .../rnscreens/ScreenStackHeaderConfig.java    |  5 +----
 2 files changed, 22 insertions(+), 4 deletions(-)

diff --git a/android/src/main/java/com/swmansion/rnscreens/ScreenStackFragment.java b/android/src/main/java/com/swmansion/rnscreens/ScreenStackFragment.java
index 4a2afb59..fe9b6bfa 100644
--- a/android/src/main/java/com/swmansion/rnscreens/ScreenStackFragment.java
+++ b/android/src/main/java/com/swmansion/rnscreens/ScreenStackFragment.java
@@ -11,6 +11,7 @@ import android.widget.LinearLayout;
 import androidx.annotation.Nullable;
 import androidx.appcompat.widget.Toolbar;
 import androidx.coordinatorlayout.widget.CoordinatorLayout;
+import androidx.fragment.app.Fragment;
 
 import com.facebook.react.uimanager.PixelUtil;
 import com.google.android.material.appbar.AppBarLayout;
@@ -100,6 +101,26 @@ public class ScreenStackFragment extends ScreenFragment {
     return mScreenView.isGestureEnabled();
   }
 
+  public boolean canNavigateBack() {
+    ScreenContainer container = mScreenView.getContainer();
+    if (container instanceof ScreenStack) {
+      if (((ScreenStack) container).getRootScreen() == getScreen()) {
+        // this screen is the root of the container, if it is nested we can check parent container
+        // if it is also a root or not
+        Fragment parentFragment = getParentFragment();
+        if (parentFragment instanceof ScreenStackFragment) {
+          return ((ScreenStackFragment) parentFragment).canNavigateBack();
+        } else {
+          return false;
+        }
+      } else {
+        return true;
+      }
+    } else {
+      throw new IllegalStateException("ScreenStackFragment added into a non-stack container");
+    }
+  }
+
   public void dismiss() {
     ScreenContainer container = mScreenView.getContainer();
     if (container instanceof ScreenStack) {
diff --git a/android/src/main/java/com/swmansion/rnscreens/ScreenStackHeaderConfig.java b/android/src/main/java/com/swmansion/rnscreens/ScreenStackHeaderConfig.java
index aa1819a6..d03ca296 100644
--- a/android/src/main/java/com/swmansion/rnscreens/ScreenStackHeaderConfig.java
+++ b/android/src/main/java/com/swmansion/rnscreens/ScreenStackHeaderConfig.java
@@ -139,9 +139,6 @@ public class ScreenStackHeaderConfig extends ViewGroup {
       return;
     }
 
-    boolean isRoot = stack == null ? true : stack.getRootScreen() == parent;
-    boolean isNested = (parent.getFragment().getParentFragment() instanceof ScreenStackFragment);
-
     if (mToolbar.getParent() == null) {
       getScreenFragment().setToolbar(mToolbar);
     }
@@ -151,7 +148,7 @@ public class ScreenStackHeaderConfig extends ViewGroup {
     ActionBar actionBar = activity.getSupportActionBar();
 
     // hide back button
-    actionBar.setDisplayHomeAsUpEnabled((isRoot && !isNested) ? false : !mIsBackButtonHidden);
+    actionBar.setDisplayHomeAsUpEnabled(getScreenFragment().canNavigateBack() ? !mIsBackButtonHidden : false);
 
     // when setSupportActionBar is called a toolbar wrapper gets initialized that overwrites
     // navigation click listener. The default behavior set in the wrapper is to call into