[jni] Fix the context when using multiple flutter engines (#2494)

Author: HosseinYousefi

.github/workflows/jnigen.yaml

@@ -90,12 +90,6 @@ jobs:
           distribution: 'zulu'
           java-version: '17'
           cache: maven
-      ## Committed bindings are formatted with clang-format.
-      ## So this is required to format generated bindings identically
-      - name: install clang tools
-        run: |
-          sudo apt-get update -y
-          sudo apt-get install -y clang-format
       - name: Install dependencies
         run: dart pub get
       - name: build in_app_java APK
@@ -172,8 +166,11 @@ jobs:
           working-directory: ./pkgs/jni
       - name: install clang tools & CMake
         run: |
+          wget https://apt.llvm.org/llvm.sh
+          chmod +x llvm.sh
+          sudo ./llvm.sh 20
           sudo apt-get update -y
-          sudo apt-get install -y clang-format build-essential cmake
+          sudo apt-get install -y clang-format-20 build-essential cmake
       - run: flutter pub get
       - name: Check formatting
         run: dart format --output=none --set-exit-if-changed .
@@ -224,6 +221,14 @@ jobs:
           github-token: ${{ secrets.GITHUB_TOKEN }}
           parallel: true
           path-to-lcov: ./pkgs/jni/coverage/lcov.info
+      - name: building the example project succeeds
+        working-directory: ./pkgs/jni/example/
+        run: |
+          flutter build apk
+      - name: regenerate & compare jnigen bindings
+        run: |
+          dart run tool/generate_jni_bindings.dart
+          git diff --exit-code -- lib/src/plugin
       # TODO(https://github.com/dart-lang/ffigen/issues/555): FFIgen generated
       # on my machine has macOS specific stuff and CI does not.
       # We should just generate the struct as opaque, but we currently can't.
@@ -419,7 +424,7 @@ jobs:
           java-version: '17'
       - run: |
           sudo apt-get update -y
-          sudo apt-get install -y ninja-build libgtk-3-dev clang-format
+          sudo apt-get install -y ninja-build libgtk-3-dev
       - run: flutter config --enable-linux-desktop
       - run: dart pub get
       - name: Generate full bindings

pkgs/jni/CHANGELOG.md

@@ -3,6 +3,10 @@
 - **Breaking Change**: Made `Jni.env` internal.
 - **Breaking Change**: Renamed `JObjType` to `JType`.
 - **Breaking Change**: Made all of the type classes internal.
+- **Breaking Change**: Removed `Jni.getApplicationClassLoader()`,
+  `Jni.getCurrentActivity()`, and `Jni.getCachedApplicationContext()`. Instead
+  use `Jni.androidApplicationContext(engineId)` to access the application
+  context and use `Jni.androidActivity(engineId)` to acccess the activity.
 - Update to the latest lints.
 
 ## 0.14.2
@@ -13,12 +17,13 @@
 
 ## 0.14.1
 
-- Updated `bin/setup.dart` to use Gradle instead of Maven for building Java sources. Added gradle executables 
-  and bootstrap jars [#2003](https://github.com/dart-lang/native/issues/2003)
-- Added `JObject.isInstanceOf` which checks whether a `JObject` is an instance 
+- Updated `bin/setup.dart` to use Gradle instead of Maven for building Java
+  sources. Added gradle executables and bootstrap jars
+  [#2003](https://github.com/dart-lang/native/issues/2003)
+- Added `JObject.isInstanceOf` which checks whether a `JObject` is an instance
   of a java class.
-- Fixed a [bug](https://github.com/dart-lang/native/issues/1908) where
-  Java interfaces implemented in on the main thread in Dart could deadlock when
+- Fixed a [bug](https://github.com/dart-lang/native/issues/1908) where Java
+  interfaces implemented in on the main thread in Dart could deadlock when
   invoked from the main thread outside the context of a Dart isolate.
 
 ## 0.14.0

pkgs/jni/android/src/main/java/com/github/dart_lang/jni/JniPlugin.java

@@ -7,48 +7,72 @@
 import android.app.Activity;
 import android.content.Context;
 import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
 import io.flutter.embedding.engine.plugins.FlutterPlugin;
 import io.flutter.embedding.engine.plugins.activity.ActivityAware;
 import io.flutter.embedding.engine.plugins.activity.ActivityPluginBinding;
+import java.util.Objects;
+import java.util.concurrent.ConcurrentHashMap;
 
 public class JniPlugin implements FlutterPlugin, ActivityAware {
+  private static final ConcurrentHashMap<Long, JniPlugin> pluginMap = new ConcurrentHashMap<>();
+
+  private long engineId;
+  private volatile Context context;
+  private volatile Activity activity;
+
+  public static @NonNull Context getApplicationContext(long engineId) {
+    return Objects.requireNonNull(pluginMap.get(engineId)).context;
+  }
+
+  public static @Nullable Activity getActivity(long engineId) {
+    return Objects.requireNonNull(pluginMap.get(engineId)).activity;
+  }
 
   @Override
+  @SuppressWarnings("deprecation")
   public void onAttachedToEngine(@NonNull FlutterPluginBinding binding) {
-    setup(binding.getApplicationContext());
+    //noinspection deprecation
+    engineId = binding.getFlutterEngine().getEngineId();
+    context = binding.getApplicationContext();
+    pluginMap.put(engineId, this);
   }
 
-  private void setup(Context context) {
-    initializeJni(context, getClass().getClassLoader());
+  @Override
+  public void onDetachedFromEngine(@NonNull FlutterPluginBinding binding) {
+    context = null;
+    activity = null;
+    pluginMap.remove(engineId);
   }
 
-  @Override
-  public void onDetachedFromEngine(@NonNull FlutterPluginBinding binding) {}
+  private void setActivity(Activity newActivity) {
+    activity = newActivity;
+  }
 
-  // Activity handling methods
   @Override
   public void onAttachedToActivity(@NonNull ActivityPluginBinding binding) {
-    Activity activity = binding.getActivity();
-    setJniActivity(activity, activity.getApplicationContext());
+    setActivity(binding.getActivity());
   }
 
   @Override
-  public void onDetachedFromActivityForConfigChanges() {}
+  public void onDetachedFromActivityForConfigChanges() {
+    setActivity(null);
+  }
 
   @Override
   public void onReattachedToActivityForConfigChanges(@NonNull ActivityPluginBinding binding) {
-    Activity activity = binding.getActivity();
-    setJniActivity(activity, activity.getApplicationContext());
+    setActivity(binding.getActivity());
   }
 
   @Override
-  public void onDetachedFromActivity() {}
-
-  native void initializeJni(Context context, ClassLoader classLoader);
+  public void onDetachedFromActivity() {
+    setActivity(null);
+  }
 
-  native void setJniActivity(Activity activity, Context context);
+  static native void setClassLoader(ClassLoader classLoader);
 
   static {
     System.loadLibrary("dartjni");
+    setClassLoader(JniPlugin.class.getClassLoader());
   }
 }

pkgs/jni/example/android/settings.gradle

@@ -19,7 +19,7 @@ pluginManagement {
 plugins {
     id "dev.flutter.flutter-plugin-loader" version "1.0.0"
     id "com.android.application" version "8.6.0" apply false
-    id "org.jetbrains.kotlin.android" version "1.8.10" apply false
+    id "org.jetbrains.kotlin.android" version "2.1.0" apply false
 }
 
 include ":app"

pkgs/jni/example/lib/main.dart

@@ -5,6 +5,7 @@
 // ignore_for_file: library_private_types_in_public_api
 
 import 'dart:io';
+import 'dart:ui';
 
 import 'package:flutter/material.dart';
 import 'package:jni/jni.dart';
@@ -32,36 +33,42 @@ String backAndForth() {
 }
 
 void quit() {
-  JObject.fromReference(Jni.getCurrentActivity()).use((ac) =>
-      ac.jClass.instanceMethodId("finish", "()V").call(ac, jvoid.type, []));
+  final activity = Jni.androidActivity(PlatformDispatcher.instance.engineId!);
+  if (activity == null) return;
+  activity.jClass
+      .instanceMethodId("finish", "()V")
+      .call(activity, jvoid.type, []);
+  activity.release();
 }
 
 void showToast(String text) {
-  // This is example for calling your app's custom java code.
-  // Place the Toaster class in the app's android/ source Folder, with a Keep
-  // annotation or appropriate proguard rules to retain classes in release mode.
-  //
-  // In this example, Toaster class wraps android.widget.Toast so that it
-  // can be called from any thread. See
-  // android/app/src/main/java/com/github/dart_lang/jni_example/Toaster.java
+  final activity = Jni.androidActivity(PlatformDispatcher.instance.engineId!);
+  if (activity == null) return;
   final toasterClass =
       JClass.forName('com/github/dart_lang/jni_example/Toaster');
   final makeText = toasterClass.staticMethodId(
       'makeText',
       '(Landroid/app/Activity;Landroid/content/Context;'
           'Ljava/lang/CharSequence;I)'
           'Lcom/github/dart_lang/jni_example/Toaster;');
-  final toaster = makeText.call(toasterClass, JObject.type, [
-    Jni.getCurrentActivity(),
-    Jni.getCachedApplicationContext(),
-    '😀'.toJString(),
+  final applicationContext =
+      Jni.androidApplicationContext(PlatformDispatcher.instance.engineId!);
+  final toaster = makeText(toasterClass, JObject.type, [
+    activity,
+    applicationContext,
+    text.toJString(),
     0,
   ]);
   final show = toasterClass.instanceMethodId('show', '()V');
   show(toaster, jvoid.type, []);
+  toaster.release();
+  applicationContext.release();
+  activity.release();
+  text.toJString().release();
 }
 
 void main() {
+  WidgetsFlutterBinding.ensureInitialized();
   if (!Platform.isAndroid) {
     Jni.spawn();
   }
@@ -80,13 +87,22 @@ void main() {
       }),
       Example(
         "Package name",
-        () => JObject.fromReference(Jni.getCurrentActivity()).use((activity) =>
-            activity.jClass
-                .instanceMethodId("getPackageName", "()Ljava/lang/String;")
-                .call(activity, JString.type, [])),
+        () {
+          final activity =
+              Jni.androidActivity(PlatformDispatcher.instance.engineId!);
+          if (activity == null) return "Activity not available";
+          final packageName = activity.jClass
+              .instanceMethodId("getPackageName", "()Ljava/lang/String;")
+              .call(activity, JString.type, []);
+          activity.release();
+          return packageName;
+        },
+      ),
+      Example(
+        "Show toast",
+        () => showToast("Hello from JNI!"),
+        runInitially: false,
       ),
-      Example("Show toast", () => showToast("Hello from JNI!"),
-          runInitially: false),
       Example(
         "Quit",
         quit,
@@ -104,20 +120,10 @@ class Example {
   Example(this.title, this.callback, {this.runInitially = true});
 }
 
-class MyApp extends StatefulWidget {
+class MyApp extends StatelessWidget {
   const MyApp(this.examples, {super.key});
   final List<Example> examples;
 
-  @override
-  _MyAppState createState() => _MyAppState();
-}
-
-class _MyAppState extends State<MyApp> {
-  @override
-  void initState() {
-    super.initState();
-  }
-
   @override
   Widget build(BuildContext context) {
     return MaterialApp(
@@ -126,11 +132,12 @@ class _MyAppState extends State<MyApp> {
           title: const Text('JNI Examples'),
         ),
         body: ListView.builder(
-            itemCount: widget.examples.length,
-            itemBuilder: (context, i) {
-              final eg = widget.examples[i];
-              return ExampleCard(eg);
-            }),
+          itemCount: examples.length,
+          itemBuilder: (context, i) {
+            final eg = examples[i];
+            return ExampleCard(eg);
+          },
+        ),
       ),
     );
   }