Make Flutter module template use FlutterView with less assumptions (#18883)

packages/flutter_tools/templates/module/android/Flutter.tmpl/build.gradle.tmpl

@@ -45,4 +45,5 @@ flutter {
 dependencies {
     testImplementation 'junit:junit:4.12'
     implementation 'com.android.support:support-v13:27.1.1'
+    implementation 'com.android.support:support-annotations:27.1.1'
 }

packages/flutter_tools/templates/module/android/Flutter.tmpl/src/main/java/io/flutter/facade/Flutter.java

@@ -6,10 +6,10 @@ import android.arch.lifecycle.LifecycleObserver;
 import android.arch.lifecycle.OnLifecycleEvent;
 import android.content.Context;
 import android.os.Bundle;
-import android.support.v4.app.Fragment;
-import android.view.View;
+import android.support.annotation.NonNull;
 
-import io.flutter.app.FlutterActivityDelegate;
+import io.flutter.plugin.common.BasicMessageChannel;
+import io.flutter.plugin.common.StringCodec;
 import io.flutter.view.FlutterMain;
 import io.flutter.view.FlutterNativeView;
 import io.flutter.view.FlutterView;
@@ -27,72 +27,101 @@ public final class Flutter {
     // to prevent instantiation
   }
 
-  public static void startInitialization(Context applicationContext) {
+  /**
+   * Initiates the Dart VM. Calling this method at an early point may help decreasing time to first
+   * frame for a subsequently created {@link FlutterView}.
+   *
+   * @param applicationContext the application's {@link Context}
+   */
+  public static void startInitialization(@NonNull Context applicationContext) {
     FlutterMain.startInitialization(applicationContext, null);
   }
 
-  public static Fragment createFragment(String route) {
+  /**
+   * Creates a {@link FlutterFragment} managing a {@link FlutterView}. The optional
+   * initial route string will be made available to the Dart code
+   * (via {@code window.defaultRouteName}) and may be used to determine which widget
+   * should be displayed in the view. The default initialRoute is "/".
+   *
+   * @param initialRoute an initial route {@link String}, or null
+   * @return a {@link FlutterFragment}
+   */
+  @NonNull
+  public static FlutterFragment createFragment(String initialRoute) {
     final FlutterFragment fragment = new FlutterFragment();
     final Bundle args = new Bundle();
-    args.putString(FlutterFragment.ARG_ROUTE, route);
+    args.putString(FlutterFragment.ARG_ROUTE, initialRoute);
     fragment.setArguments(args);
     return fragment;
   }
 
-  public static View createView(final Activity activity, final Lifecycle lifecycle, final String route) {
+  /**
+   * Creates a {@link FlutterView} linked to the specified {@link Activity} and {@link Lifecycle}.
+   * The optional initial route string will be made available to the Dart code (via
+   * {@code window.defaultRouteName}) and may be used to determine which widget should be displayed
+   * in the view. The default initialRoute is "/".
+   *
+   * @param activity an {@link Activity}
+   * @param lifecycle a {@link Lifecycle}
+   * @param initialRoute an initial route {@link String}, or null
+   * @return a {@link FlutterView}
+   */
+  @NonNull
+  public static FlutterView createView(@NonNull final Activity activity, @NonNull final Lifecycle lifecycle, final String initialRoute) {
     FlutterMain.startInitialization(activity.getApplicationContext());
     FlutterMain.ensureInitializationComplete(activity.getApplicationContext(), null);
-    final FlutterActivityDelegate delegate = new FlutterActivityDelegate(activity, new FlutterActivityDelegate.ViewFactory() {
+    final FlutterNativeView nativeView = new FlutterNativeView(activity);
+    final FlutterView flutterView = new FlutterView(activity, null, nativeView) {
+      private final BasicMessageChannel<String> lifecycleMessages = new BasicMessageChannel<>(this, "flutter/lifecycle", StringCodec.INSTANCE);
       @Override
-      public FlutterView createFlutterView(Context context) {
-        final FlutterNativeView nativeView = new FlutterNativeView(context);
-        final FlutterView flutterView = new FlutterView(activity, null, nativeView);
-        flutterView.setInitialRoute(route);
-        return flutterView;
+      public void onFirstFrame() {
+        super.onFirstFrame();
+        setAlpha(1.0f);
       }
 
       @Override
-      public boolean retainFlutterNativeView() {
-        return false;
+      public void onPostResume() {
+        // Overriding default behavior to avoid dictating system UI via PlatformPlugin.
+        lifecycleMessages.send("AppLifecycleState.resumed");
       }
-
-      @Override
-      public FlutterNativeView createFlutterNativeView() {
-        throw new UnsupportedOperationException();
-      }
-    });
+    };
+    if (initialRoute != null) {
+      flutterView.setInitialRoute(initialRoute);
+    }
     lifecycle.addObserver(new LifecycleObserver() {
       @OnLifecycleEvent(Lifecycle.Event.ON_CREATE)
       public void onCreate() {
-        delegate.onCreate(null);
-        GeneratedPluginRegistrant.registerWith(delegate);
+        final String appBundlePath = FlutterMain.findAppBundlePath(activity.getApplicationContext());
+        flutterView.runFromBundle(appBundlePath, null, "main", true);
+        GeneratedPluginRegistrant.registerWith(flutterView.getPluginRegistry());
       }
 
       @OnLifecycleEvent(Lifecycle.Event.ON_START)
       public void onStart() {
-        delegate.onStart();
+        flutterView.onStart();
       }
 
       @OnLifecycleEvent(Lifecycle.Event.ON_RESUME)
       public void onResume() {
-        delegate.onResume();
+        flutterView.onPostResume();
       }
 
       @OnLifecycleEvent(Lifecycle.Event.ON_PAUSE)
       public void onPause() {
-        delegate.onPause();
+        flutterView.onPause();
       }
 
       @OnLifecycleEvent(Lifecycle.Event.ON_STOP)
       public void onStop() {
-        delegate.onStop();
+        flutterView.onStop();
       }
 
       @OnLifecycleEvent(Lifecycle.Event.ON_DESTROY)
       public void onDestroy() {
-        delegate.onDestroy();
+        flutterView.destroy();
       }
     });
-    return delegate.getFlutterView();
+    flutterView.setAlpha(0.0f);
+    return flutterView;
   }
 }

packages/flutter_tools/templates/module/android/Flutter.tmpl/src/main/java/io/flutter/facade/FlutterFragment.java

@@ -2,14 +2,16 @@ package io.flutter.facade;
 
 import android.content.Context;
 import android.os.Bundle;
+import android.support.annotation.NonNull;
 import android.support.v4.app.Fragment;
 import android.util.AttributeSet;
 import android.view.LayoutInflater;
-import android.view.View;
 import android.view.ViewGroup;
 
+import io.flutter.view.FlutterView;
+
 /**
- * A {@link Fragment} managing a Flutter view.
+ * A {@link Fragment} managing a {@link FlutterView}.
  *
  * <p><strong>Warning:</strong> This file is auto-generated by Flutter tooling. Do not edit.
  * It may be moved into flutter.jar or another library dependency of the Flutter module project
@@ -33,8 +35,7 @@ public class FlutterFragment extends Fragment {
   }
 
   @Override
-  public View onCreateView(LayoutInflater inflater, ViewGroup container,
-                           Bundle savedInstanceState) {
+  public FlutterView onCreateView(@NonNull LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
     return Flutter.createView(getActivity(), getLifecycle(), mRoute);
   }
 }