Ensure content-sizing resize is run on UI thread (flutter#181686)

While testing with a different add-to-app
flutter/samples#2787, an exception is sometimes
thrown when the resize is attempted because the callback comes from a
different thread. It is expected that the raster thread calls this but
with previous
[testing](https://github.com/mboetger/test-add-to-app/tree/content-sizing)
never caused this exception.

This PR ensures the resize happens on the UI thread. It also a flag to
ensure content sizing is disabled.

Fixes: flutter#181573

## Pre-launch Checklist

- [X] I read the [Contributor Guide] and followed the process outlined
there for submitting PRs.
- [X] I read the [Tree Hygiene] wiki page, which explains my
responsibilities.
- [X] I read and followed the [Flutter Style Guide], including [Features
we expect every widget to implement].
- [X] I signed the [CLA].
- [X] I listed at least one issue that this PR fixes in the description
above.
- [X] I updated/added relevant documentation (doc comments with `///`).
- [X] I added new tests to check the change I am making, or this PR is
[test-exempt].
- [X] I followed the [breaking change policy] and added [Data Driven
Fixes] where supported.
- [X] All existing and new tests are passing.

Author: mboetger

engine/src/flutter/shell/platform/android/BUILD.gn

@@ -221,6 +221,7 @@ android_java_sources = [
   "io/flutter/Log.java",
   "io/flutter/app/FlutterApplication.java",
   "io/flutter/embedding/android/AndroidTouchProcessor.java",
+  "io/flutter/embedding/android/ContentSizingFlag.java",
   "io/flutter/embedding/android/ExclusiveAppComponent.java",
   "io/flutter/embedding/android/FlutterActivity.java",
   "io/flutter/embedding/android/FlutterActivityAndFragmentDelegate.java",

engine/src/flutter/shell/platform/android/external_view_embedder/external_view_embedder.cc

@@ -7,6 +7,7 @@
 #include "flutter/common/constants.h"
 #include "flutter/fml/synchronization/waitable_event.h"
 #include "flutter/fml/trace_event.h"
+#include "fml/make_copyable.h"
 
 namespace flutter {
 
@@ -225,7 +226,11 @@ void AndroidExternalViewEmbedder::PrepareFlutterView(
     DestroySurfaces();
   }
   surface_pool_->SetFrameSize(frame_size);
-  jni_facade_->MaybeResizeSurfaceView(frame_size.width, frame_size.height);
+
+  task_runners_.GetPlatformTaskRunner()->PostTask(
+      fml::MakeCopyable([jni_facade = jni_facade_, frame_size = frame_size]() {
+        jni_facade->MaybeResizeSurfaceView(frame_size.width, frame_size.height);
+      }));
 
   frame_size_ = frame_size;
   device_pixel_ratio_ = device_pixel_ratio;

engine/src/flutter/shell/platform/android/external_view_embedder/external_view_embedder_2.cc

@@ -245,7 +245,11 @@ void AndroidExternalViewEmbedder2::PrepareFlutterView(
     DestroySurfaces();
   }
   surface_pool_->SetFrameSize(frame_size);
-  jni_facade_->MaybeResizeSurfaceView(frame_size.width, frame_size.height);
+
+  task_runners_.GetPlatformTaskRunner()->PostTask(
+      fml::MakeCopyable([jni_facade = jni_facade_, frame_size = frame_size]() {
+        jni_facade->MaybeResizeSurfaceView(frame_size.width, frame_size.height);
+      }));
 
   frame_size_ = frame_size;
   device_pixel_ratio_ = device_pixel_ratio;

engine/src/flutter/shell/platform/android/external_view_embedder/external_view_embedder_unittests.cc

@@ -11,10 +11,13 @@
 #include "flutter/flow/embedded_views.h"
 #include "flutter/flow/surface.h"
 #include "flutter/fml/raster_thread_merger.h"
+#include "flutter/fml/synchronization/waitable_event.h"
 #include "flutter/fml/thread.h"
+#include "flutter/shell/common/thread_host.h"
 #include "flutter/shell/platform/android/jni/jni_mock.h"
 #include "flutter/shell/platform/android/surface/android_surface.h"
 #include "flutter/shell/platform/android/surface/android_surface_mock.h"
+#include "flutter/testing/testing.h"
 
 #include "gmock/gmock.h"
 #include "gtest/gtest.h"
@@ -1068,8 +1071,18 @@ TEST(AndroidExternalViewEmbedder, Teardown) {
 TEST(AndroidExternalViewEmbedder, MaybeResizeSurfaceView) {
   auto jni_mock = std::make_shared<JNIMock>();
   auto android_context = AndroidContext(AndroidRenderingAPI::kSoftware);
+  ThreadHost thread_host("io.flutter.test." + GetCurrentTestName() + ".",
+                         ThreadHost::Type::kPlatform | ThreadHost::Type::kIo |
+                             ThreadHost::Type::kUi | ThreadHost::Type::kRaster);
+  TaskRunners task_runners(
+      "test",
+      thread_host.platform_thread->GetTaskRunner(),  // platform
+      thread_host.raster_thread->GetTaskRunner(),    // raster
+      thread_host.ui_thread->GetTaskRunner(),        // ui
+      thread_host.io_thread->GetTaskRunner()         // io
+  );
   auto embedder = std::make_unique<AndroidExternalViewEmbedder>(
-      android_context, jni_mock, nullptr, GetTaskRunnersForFixture());
+      android_context, jni_mock, nullptr, task_runners);
 
   fml::Thread rasterizer_thread("rasterizer");
   auto raster_thread_merger =
@@ -1081,6 +1094,11 @@ TEST(AndroidExternalViewEmbedder, MaybeResizeSurfaceView) {
 
   EXPECT_CALL(*jni_mock, MaybeResizeSurfaceView(100, 200));
   embedder->PrepareFlutterView(DlISize(100, 200), 1.0);
+
+  fml::AutoResetWaitableEvent latch;
+  fml::TaskRunner::RunNowOrPostTask(task_runners.GetPlatformTaskRunner(),
+                                    [&latch]() { latch.Signal(); });
+  latch.Wait();
 }
 
 TEST(AndroidExternalViewEmbedder, TeardownDoesNotCallJNIMethod) {

engine/src/flutter/shell/platform/android/io/flutter/embedding/android/ContentSizingFlag.java

@@ -0,0 +1,39 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package io.flutter.embedding.android;
+
+import android.content.Context;
+import android.content.pm.ApplicationInfo;
+import android.content.pm.PackageManager;
+import android.content.pm.PackageManager.NameNotFoundException;
+import android.os.Bundle;
+import io.flutter.Log;
+
+class ContentSizingFlag {
+
+  private static final String TAG = "ContentSizingFlag";
+
+  // Default to DISABLED
+  private static final boolean DEFAULT = false;
+
+  private static final String ENABLE_CONTENT_SIZING =
+      "io.flutter.embedding.android.EnableContentSizing";
+
+  static boolean isEnabled(Context context) {
+    // Ensure that the context is actually the application context.
+    final Context appContext = context.getApplicationContext();
+    Bundle metaData = null;
+    try {
+      ApplicationInfo applicationInfo =
+          appContext
+              .getPackageManager()
+              .getApplicationInfo(appContext.getPackageName(), PackageManager.GET_META_DATA);
+      metaData = applicationInfo.metaData;
+    } catch (NameNotFoundException ex) {
+      Log.e(TAG, "Could not get metadata");
+    }
+    return metaData != null ? metaData.getBoolean(ENABLE_CONTENT_SIZING, DEFAULT) : DEFAULT;
+  }
+}

engine/src/flutter/shell/platform/android/io/flutter/embedding/android/FlutterImageView.java

@@ -47,6 +47,8 @@ public class FlutterImageView extends View implements RenderSurface {
   @Nullable private Bitmap currentBitmap;
   @Nullable private FlutterRenderer flutterRenderer;
 
+  private boolean isContentSizingEnabled = false;
+
   public ImageReader getImageReader() {
     return imageReader;
   }
@@ -92,11 +94,16 @@ public FlutterImageView(@NonNull Context context, @NonNull AttributeSet attrs) {
 
   private void init() {
     setAlpha(0.0f);
+    isContentSizingEnabled = ContentSizingFlag.isEnabled(getContext());
   }
 
   @Override
   protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
-    FlutterMeasureSpec.onMeasure(widthMeasureSpec, heightMeasureSpec, this::setMeasuredDimension);
+    if (isContentSizingEnabled) {
+      FlutterMeasureSpec.onMeasure(widthMeasureSpec, heightMeasureSpec, this::setMeasuredDimension);
+    } else {
+      super.onMeasure(widthMeasureSpec, heightMeasureSpec);
+    }
   }
 
   private static void logW(String format, Object... args) {

engine/src/flutter/shell/platform/android/io/flutter/embedding/android/FlutterSurfaceView.java

@@ -40,6 +40,8 @@ public class FlutterSurfaceView extends SurfaceView implements RenderSurface {
   private boolean isPaused = false;
   @Nullable private FlutterRenderer flutterRenderer;
 
+  private boolean isContentSizingEnabled = false;
+
   private boolean shouldNotify() {
     return flutterRenderer != null && !isPaused;
   }
@@ -116,14 +118,20 @@ private void init() {
       setZOrderOnTop(true);
     }
 
+    isContentSizingEnabled = ContentSizingFlag.isEnabled(getContext());
+
     // Grab a reference to our underlying Surface and register callbacks with that Surface so we
     // can monitor changes and forward those changes on to native Flutter code.
     getHolder().addCallback(surfaceHolderCallbackCompat);
   }
 
   @Override
   protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
-    FlutterMeasureSpec.onMeasure(widthMeasureSpec, heightMeasureSpec, this::setMeasuredDimension);
+    if (isContentSizingEnabled) {
+      FlutterMeasureSpec.onMeasure(widthMeasureSpec, heightMeasureSpec, this::setMeasuredDimension);
+    } else {
+      super.onMeasure(widthMeasureSpec, heightMeasureSpec);
+    }
   }
 
   // This is a work around for TalkBack.

engine/src/flutter/shell/platform/android/io/flutter/embedding/android/FlutterTextureView.java

@@ -39,6 +39,8 @@ public class FlutterTextureView extends TextureView implements RenderSurface {
   @Nullable private FlutterRenderer flutterRenderer;
   @Nullable private Surface renderSurface;
 
+  private boolean isContentSizingEnabled = false;
+
   private boolean shouldNotify() {
     return flutterRenderer != null && !isPaused;
   }
@@ -116,11 +118,17 @@ private void init() {
     // Listen for when our underlying SurfaceTexture becomes available, changes size, or
     // gets destroyed, and take the appropriate actions.
     setSurfaceTextureListener(surfaceTextureListener);
+
+    isContentSizingEnabled = ContentSizingFlag.isEnabled(getContext());
   }
 
   @Override
   protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
-    FlutterMeasureSpec.onMeasure(widthMeasureSpec, heightMeasureSpec, this::setMeasuredDimension);
+    if (isContentSizingEnabled) {
+      FlutterMeasureSpec.onMeasure(widthMeasureSpec, heightMeasureSpec, this::setMeasuredDimension);
+    } else {
+      super.onMeasure(widthMeasureSpec, heightMeasureSpec);
+    }
   }
 
   @Nullable
@@ -273,4 +281,4 @@ private void disconnectSurfaceFromRenderer() {
       renderSurface = null;
     }
   }
-}
+}

engine/src/flutter/shell/platform/android/io/flutter/embedding/android/FlutterView.java

@@ -123,6 +123,9 @@ public class FlutterView extends FrameLayout
   // Maximum size allowed for a content sized view.
   @VisibleForTesting static final int CONTENT_SIZING_MAX = 2 << 12;
 
+  // Flag to enable content sizing.
+  @VisibleForTesting boolean isContentSizingEnabled = false;
+
   // Internal view hierarchy references.
   @Nullable private FlutterSurfaceView flutterSurfaceView;
   @Nullable private FlutterTextureView flutterTextureView;
@@ -424,6 +427,8 @@ private void init() {
       addView(flutterImageView);
     }
 
+    isContentSizingEnabled = ContentSizingFlag.isEnabled(getContext());
+
     // FlutterView needs to be focusable so that the InputMethodManager can interact with it.
     setFocusable(true);
     setFocusableInTouchMode(true);
@@ -521,15 +526,15 @@ protected void onSizeChanged(int width, int height, int oldWidth, int oldHeight)
     viewportMetrics.width = width;
     viewportMetrics.height = height;
 
-    if (heightMode == MeasureSpec.UNSPECIFIED) {
+    if (isContentSizingEnabled && heightMode == MeasureSpec.UNSPECIFIED) {
       Log.d(TAG, "FlutterView height is set to wrap content - updating viewport metrics to max");
       viewportMetrics.minHeight = 0;
       viewportMetrics.maxHeight = CONTENT_SIZING_MAX;
     } else {
       viewportMetrics.minHeight = viewportMetrics.height;
       viewportMetrics.maxHeight = viewportMetrics.height;
     }
-    if (widthMode == MeasureSpec.UNSPECIFIED) {
+    if (isContentSizingEnabled && widthMode == MeasureSpec.UNSPECIFIED) {
       Log.d(TAG, "FlutterView width is set to wrap content - updating viewport metrics to max");
       viewportMetrics.minWidth = 0;
       viewportMetrics.maxWidth = CONTENT_SIZING_MAX;

engine/src/flutter/shell/platform/android/io/flutter/embedding/engine/FlutterJNI.java

@@ -1328,8 +1328,8 @@ public void destroyOverlaySurfaces() {
     platformViewsController.destroyOverlaySurfaces();
   }
 
-  // This will get called on the raster thread.
   @SuppressWarnings("unused")
+  @UiThread
   public void maybeResizeSurfaceView(int width, int height) {
     for (FlutterUiResizeListener listener : flutterUiResizeListeners) {
       listener.resizeEngineView(width, height);