View destroy listener (flutter#4347)

[Android] Allow persisting a FlutterNativeView across activities.

shell/platform/android/io/flutter/app/FlutterActivity.java

@@ -12,6 +12,7 @@
 import io.flutter.app.FlutterActivityDelegate.ViewFactory;
 import io.flutter.plugin.common.PluginRegistry;
 import io.flutter.plugin.common.PluginRegistry.Registrar;
+import io.flutter.view.FlutterNativeView;
 import io.flutter.view.FlutterView;
 
 /**
@@ -47,6 +48,18 @@ public FlutterView createFlutterView(Context context) {
         return null;
     }
 
+    /**
+     * Hook for subclasses to customize the creation of the
+     * {@code FlutterNativeView}.
+     *
+     * <p>The default implementation returns {@code null}, which will cause the
+     * activity to use a newly instantiated native view object.</p>
+     */
+    @Override
+    public FlutterNativeView createFlutterNativeView() {
+        return null;
+    }
+
     @Override
     public final boolean hasPlugin(String key) {
         return pluginRegistry.hasPlugin(key);
@@ -68,6 +81,12 @@ protected void onCreate(Bundle savedInstanceState) {
         eventDelegate.onCreate(savedInstanceState);
     }
 
+    @Override
+    protected void onResume() {
+        super.onResume();
+        eventDelegate.onResume();
+    }
+
     @Override
     protected void onDestroy() {
         eventDelegate.onDestroy();

shell/platform/android/io/flutter/app/FlutterActivityDelegate.java

@@ -7,6 +7,7 @@
 import android.animation.Animator;
 import android.animation.AnimatorListenerAdapter;
 import android.app.Activity;
+import android.app.Application;
 import android.content.Context;
 import android.content.Intent;
 import android.content.pm.ActivityInfo;
@@ -34,6 +35,7 @@
 import io.flutter.plugin.platform.PlatformPlugin;
 import io.flutter.util.Preconditions;
 import io.flutter.view.FlutterMain;
+import io.flutter.view.FlutterNativeView;
 import io.flutter.view.FlutterView;
 import io.flutter.view.TextureRegistry;
 
@@ -75,9 +77,16 @@ public final class FlutterActivityDelegate
      * <p>A delegate's view factory will be consulted during
      * {@link #onCreate(Bundle)}. If it returns {@code null}, then the delegate
      * will fall back to instantiating a new full-screen {@code FlutterView}.</p>
+     *
+     * <p>A delegate's native view factory will be consulted during
+     * {@link #onCreate(Bundle)}. If it returns {@code null}, then the delegate
+     * will fall back to instantiating a new {@code FlutterNativeView}. This is
+     * useful for applications to override to reuse the FlutterNativeView held
+     * e.g. by a pre-existing background service.</p>
      */
     public interface ViewFactory {
         FlutterView createFlutterView(Context context);
+        FlutterNativeView createFlutterNativeView();
     }
 
     private final Activity activity;
@@ -87,6 +96,7 @@ public interface ViewFactory {
     private final List<ActivityResultListener> activityResultListeners = new ArrayList<>(0);
     private final List<NewIntentListener> newIntentListeners = new ArrayList<>(0);
     private final List<UserLeaveHintListener> userLeaveHintListeners = new ArrayList<>(0);
+    private final List<ViewDestroyListener> viewDestroyListeners = new ArrayList<>(0);
 
     private FlutterView flutterView;
     private View launchView;
@@ -156,7 +166,8 @@ public void onCreate(Bundle savedInstanceState) {
 
         flutterView = viewFactory.createFlutterView(activity);
         if (flutterView == null) {
-            flutterView = new FlutterView(activity);
+            FlutterNativeView nativeView = viewFactory.createFlutterNativeView();
+            flutterView = new FlutterView(activity, null, nativeView);
             flutterView.setLayoutParams(matchParent);
             activity.setContentView(flutterView);
             launchView = createLaunchView();
@@ -165,12 +176,18 @@ public void onCreate(Bundle savedInstanceState) {
             }
         }
 
-        if (loadIntent(activity.getIntent())) {
+        // When an activity is created for the first time, we direct the
+        // FlutterView to re-use a pre-existing Isolate rather than create a new
+        // one. This is so that an Isolate coming in from the ViewFactory is
+        // used.
+        final boolean reuseIsolate = true;
+
+        if (loadIntent(activity.getIntent(), reuseIsolate)) {
             return;
         }
         String appBundlePath = FlutterMain.findAppBundlePath(activity.getApplicationContext());
         if (appBundlePath != null) {
-            flutterView.runFromBundle(appBundlePath, null);
+            flutterView.runFromBundle(appBundlePath, null, "main", reuseIsolate);
         }
     }
 
@@ -193,13 +210,29 @@ private boolean isDebuggable() {
 
     @Override
     public void onPause() {
+        Application app = (Application) activity.getApplicationContext();
+        if (app instanceof FlutterApplication) {
+            FlutterApplication flutterApp = (FlutterApplication) app;
+            if (this.equals(flutterApp.getCurrentActivity())) {
+                Log.i(TAG, "onPause setting current activity to null");
+                flutterApp.setCurrentActivity(null);
+            }
+        }
         if (flutterView != null) {
             flutterView.onPause();
         }
     }
 
     @Override
     public void onResume() {
+        Application app = (Application) activity.getApplicationContext();
+        if (app instanceof FlutterApplication) {
+            FlutterApplication flutterApp = (FlutterApplication) app;
+            Log.i(TAG, "onResume setting current activity to this");
+            flutterApp.setCurrentActivity(activity);
+        } else {
+            Log.i(TAG, "onResume app wasn't a FlutterApplication!!");
+        }
     }
 
     @Override
@@ -211,8 +244,26 @@ public void onPostResume() {
 
     @Override
     public void onDestroy() {
+        Application app = (Application) activity.getApplicationContext();
+        if (app instanceof FlutterApplication) {
+            FlutterApplication flutterApp = (FlutterApplication) app;
+            if (this.equals(flutterApp.getCurrentActivity())) {
+                Log.i(TAG, "onDestroy setting current activity to null");
+                flutterApp.setCurrentActivity(null);
+            }
+        }
         if (flutterView != null) {
-            flutterView.destroy();
+            boolean destroy = true;
+            for (ViewDestroyListener listener : viewDestroyListeners) {
+                destroy = destroy && !listener.onViewDestroy(flutterView.getFlutterNativeView());
+            }
+            if (destroy) {
+                flutterView.destroy();
+            } else {
+                // Detach, but do not destroy the FlutterView if a plugin
+                // expressed interest in its FlutterNativeView.
+                flutterView.detach();
+            }
         }
     }
 
@@ -278,6 +329,11 @@ private static String[] getArgsFromIntent(Intent intent) {
     }
 
     private boolean loadIntent(Intent intent) {
+        final boolean reuseIsolate = false;
+        return loadIntent(intent, reuseIsolate);
+    }
+
+    private boolean loadIntent(Intent intent, boolean reuseIsolate) {
         String action = intent.getAction();
         if (Intent.ACTION_RUN.equals(action)) {
             String route = intent.getStringExtra("route");
@@ -290,7 +346,7 @@ private boolean loadIntent(Intent intent) {
             if (route != null) {
                 flutterView.setInitialRoute(route);
             }
-            flutterView.runFromBundle(appBundlePath, intent.getStringExtra("snapshot"));
+            flutterView.runFromBundle(appBundlePath, intent.getStringExtra("snapshot"), "main", reuseIsolate);
             return true;
         }
 
@@ -476,5 +532,11 @@ public Registrar addUserLeaveHintListener(UserLeaveHintListener listener) {
             userLeaveHintListeners.add(listener);
             return this;
         }
+
+        @Override
+        public Registrar addViewDestroyListener(ViewDestroyListener listener) {
+            viewDestroyListeners.add(listener);
+            return this;
+        }
     }
 }

shell/platform/android/io/flutter/app/FlutterApplication.java

@@ -4,6 +4,7 @@
 
 package io.flutter.app;
 
+import android.app.Activity;
 import android.app.Application;
 
 import io.flutter.view.FlutterMain;
@@ -18,4 +19,12 @@ public void onCreate() {
         super.onCreate();
         FlutterMain.startInitialization(this);
     }
+
+    private Activity mCurrentActivity = null;
+    public Activity getCurrentActivity() {
+        return mCurrentActivity;
+    }
+    public void setCurrentActivity(Activity mCurrentActivity) {
+        this.mCurrentActivity = mCurrentActivity;
+    }
 }

shell/platform/android/io/flutter/app/FlutterFragmentActivity.java

@@ -12,6 +12,7 @@
 import io.flutter.app.FlutterActivityDelegate.ViewFactory;
 import io.flutter.plugin.common.PluginRegistry;
 import io.flutter.plugin.common.PluginRegistry.Registrar;
+import io.flutter.view.FlutterNativeView;
 import io.flutter.view.FlutterView;
 
 /**
@@ -58,6 +59,11 @@ public FlutterView createFlutterView(Context context) {
         return null;
     }
 
+    @Override
+    public FlutterNativeView createFlutterNativeView() {
+        return null;
+    }
+
     @Override
     public final boolean hasPlugin(String key) {
         return pluginRegistry.hasPlugin(key);

shell/platform/android/io/flutter/plugin/common/PluginRegistry.java

@@ -6,6 +6,7 @@
 
 import android.app.Activity;
 import android.content.Intent;
+import io.flutter.view.FlutterNativeView;
 import io.flutter.view.FlutterView;
 import io.flutter.view.TextureRegistry;
 
@@ -140,6 +141,15 @@ interface Registrar {
          * @return this {@link Registrar}.
          */
         Registrar addUserLeaveHintListener(UserLeaveHintListener listener);
+
+        /**
+         * Adds a callback allowing the plugin to take part in handling incoming
+         * calls to {@link Activity#onDestroy()}.
+         *
+         * @param listener a {@link ViewDestroyListener} callback.
+         * @return this {@link Registrar}.
+         */
+        Registrar addViewDestroyListener(ViewDestroyListener listener);
     }
 
     /**
@@ -182,4 +192,13 @@ interface NewIntentListener {
     interface UserLeaveHintListener {
         void onUserLeaveHint();
     }
+
+    /**
+     * Delegate interface for handling an {@link Activity}'s onDestroy
+     * method being called. A plugin that implements this interface can
+     * adopt the FlutterNativeView by retaining a reference and returning true.
+     */
+    interface ViewDestroyListener {
+        boolean onViewDestroy(FlutterNativeView view);
+    }
 }

shell/platform/android/io/flutter/view/FlutterNativeView.java

@@ -11,7 +11,7 @@
 import java.util.HashMap;
 import java.util.Map;
 
-class FlutterNativeView implements BinaryMessenger {
+public class FlutterNativeView implements BinaryMessenger {
     private static final String TAG = "FlutterNativeView";
 
     private final Map<String, BinaryMessageHandler> mMessageHandlers;
@@ -21,23 +21,32 @@ class FlutterNativeView implements BinaryMessenger {
     private long mNativePlatformView;
     private FlutterView mFlutterView;
 
-    FlutterNativeView(FlutterView flutterView) {
+    public FlutterNativeView(FlutterView flutterView) {
         mFlutterView = flutterView;
         attach(this);
         assertAttached();
         mMessageHandlers = new HashMap<>();
     }
 
-    FlutterNativeView() {
+    public FlutterNativeView() {
         this(null);
     }
 
+    public void detach() {
+        mFlutterView = null;
+        nativeDetach(mNativePlatformView);
+    }
+
     public void destroy() {
         mFlutterView = null;
         nativeDestroy(mNativePlatformView);
         mNativePlatformView = 0;
     }
 
+    public void setFlutterView(FlutterView flutterView) {
+        mFlutterView = flutterView;
+    }
+
     public boolean isAttached() {
         return mNativePlatformView != 0;
     }
@@ -168,6 +177,7 @@ private void onFirstFrame() {
 
     private static native long nativeAttach(FlutterNativeView view);
     private static native void nativeDestroy(long nativePlatformViewAndroid);
+    private static native void nativeDetach(long nativePlatformViewAndroid);
 
     private static native void nativeRunBundleAndSnapshot(long nativePlatformViewAndroid,
         String bundlePath,

shell/platform/android/io/flutter/view/FlutterView.java

@@ -115,6 +115,10 @@ public FlutterView(Context context) {
     }
 
     public FlutterView(Context context, AttributeSet attrs) {
+        this(context, attrs, null);
+    }
+
+    public FlutterView(Context context, AttributeSet attrs, FlutterNativeView nativeView) {
         super(context, attrs);
 
         mIsSoftwareRenderingEnabled = nativeGetIsSoftwareRenderingEnabled();
@@ -124,7 +128,12 @@ public FlutterView(Context context, AttributeSet attrs) {
         setFocusable(true);
         setFocusableInTouchMode(true);
 
-        mNativeView = new FlutterNativeView(this);
+        if (nativeView == null) {
+            mNativeView = new FlutterNativeView(this);
+        } else {
+            mNativeView = nativeView;
+            mNativeView.setFlutterView(this);
+        }
 
         int color = 0xFF000000;
         TypedValue typedValue = new TypedValue();
@@ -235,6 +244,10 @@ public boolean onKeyDown(int keyCode, KeyEvent event) {
         return super.onKeyDown(keyCode, event);
     }
 
+    public FlutterNativeView getFlutterNativeView() {
+        return mNativeView;
+    }
+
     public void addActivityLifecycleListener(ActivityLifecycleListener listener) {
         mActivityLifecycleListeners.add(listener);
     }
@@ -310,6 +323,20 @@ float getDevicePixelRatio() {
         return mMetrics.devicePixelRatio;
     }
 
+    public FlutterNativeView detach() {
+        if (!isAttached())
+            return null;
+        if (mDiscoveryReceiver != null) {
+            getContext().unregisterReceiver(mDiscoveryReceiver);
+        }
+        getHolder().removeCallback(mSurfaceCallback);
+        mNativeView.detach();
+
+        FlutterNativeView view = mNativeView;
+        mNativeView = null;
+        return view;
+    }
+
     public void destroy() {
         if (!isAttached())
             return;