From 205d1e53397591594e400b79e16280d62b84f922 Mon Sep 17 00:00:00 2001
From: Justin McCandless <jmccandless@google.com>
Date: Wed, 1 Feb 2023 11:41:06 -0800
Subject: [PATCH] navigationStackIsEmpty method to enable predictive back

---
 .../io/flutter/embedding/android/FlutterActivity.java    | 9 ++++++++-
 .../io/flutter/embedding/android/FlutterFragment.java    | 7 +++++++
 .../io/flutter/plugin/platform/PlatformPlugin.java       | 6 ++++--
 3 files changed, 19 insertions(+), 3 deletions(-)

diff --git a/shell/platform/android/io/flutter/embedding/android/FlutterActivity.java b/shell/platform/android/io/flutter/embedding/android/FlutterActivity.java
index a94c266dde14b..ebf92d77d2168 100644
--- a/shell/platform/android/io/flutter/embedding/android/FlutterActivity.java
+++ b/shell/platform/android/io/flutter/embedding/android/FlutterActivity.java
@@ -666,7 +666,8 @@ protected void onCreate(@Nullable Bundle savedInstanceState) {
   public void registerOnBackInvokedCallback() {
     if (Build.VERSION.SDK_INT >= 33) {
       // TODO(justinmc): This is really the one and only thing that stops root
-      // pback for me.
+      // pback for me. There are probably other places you need to mess with
+      // this for other embedding strategies!
       Log.e("justin", "registerOnBackInvokedCallback");
       getOnBackInvokedDispatcher()
           .registerOnBackInvokedCallback(
@@ -674,6 +675,12 @@ public void registerOnBackInvokedCallback() {
     }
   }
 
+  @Override
+  public void navigatorIsEmpty() {
+    Log.e("justin", "navigatorIsEmpty in embedding FlutterActivity");
+    unregisterOnBackInvokedCallback();
+  }
+
   /**
    * Unregisters the callback from OnBackInvokedDispatcher.
    *
diff --git a/shell/platform/android/io/flutter/embedding/android/FlutterFragment.java b/shell/platform/android/io/flutter/embedding/android/FlutterFragment.java
index 483b5ec0f52fe..ad581197802a9 100644
--- a/shell/platform/android/io/flutter/embedding/android/FlutterFragment.java
+++ b/shell/platform/android/io/flutter/embedding/android/FlutterFragment.java
@@ -1661,6 +1661,13 @@ public boolean popSystemNavigator() {
     return false;
   }
 
+  @Override
+  public void navigatorIsEmpty() {
+    // TODO(justinmc): Implement. Implementing in FlutterActivity first.
+    // unregisterOnBackInvokedCallback();
+    Log.e("justin", "navigatorIsEmpty in embedding FlutterFragment");
+  }
+
   @VisibleForTesting
   @NonNull
   boolean shouldDelayFirstAndroidViewDraw() {
diff --git a/shell/platform/android/io/flutter/plugin/platform/PlatformPlugin.java b/shell/platform/android/io/flutter/plugin/platform/PlatformPlugin.java
index 02b61cebdb6ff..a2eec420e2325 100644
--- a/shell/platform/android/io/flutter/plugin/platform/PlatformPlugin.java
+++ b/shell/platform/android/io/flutter/plugin/platform/PlatformPlugin.java
@@ -56,6 +56,8 @@ public interface PlatformPluginDelegate {
      *     androidx.activity.OnBackPressedDispatcher} will be executed.
      */
     boolean popSystemNavigator();
+
+    void navigatorIsEmpty();
   }
 
   @VisibleForTesting
@@ -111,6 +113,7 @@ public void setSystemUiOverlayStyle(
 
         @Override
         public void navigatorIsEmpty() {
+          Log.e("justin", "navigatorIsEmpty in PlatformHandler.PlatformMessageChannel.");
           PlatformPlugin.this.navigatorIsEmpty();
         }
 
@@ -482,8 +485,7 @@ private void setSystemChromeSystemUIOverlayStyle(
 
   private void navigatorIsEmpty() {
     Log.e("justin", "navigatorIsEmpty in PlatformPlugin");
-    // TODO(justinmc): Can't quite call it like this, need FlutterActivity.
-    // activity.unregisterOnBackInvokedCallback();
+    platformPluginDelegate.navigatorIsEmpty();
   }
 
   private void popSystemNavigator() {