Add spinner to loading video (#13330)

* Add spinner to loading video

examples/flutter_gallery/lib/demo/video_demo.dart

@@ -30,7 +30,7 @@ class VideoCard extends StatelessWidget {
           aspectRatio: 3 / 2,
           child: new Hero(
             tag: controller,
-            child: new VideoPlayer(controller),
+            child: new VideoPlayerLoading(controller),
           ),
         ),
       ),
@@ -97,6 +97,50 @@ class VideoCard extends StatelessWidget {
   }
 }
 
+class VideoPlayerLoading extends StatefulWidget {
+  final VideoPlayerController controller;
+
+  const VideoPlayerLoading(this.controller);
+
+  @override
+  _VideoPlayerLoadingState createState() => new _VideoPlayerLoadingState();
+}
+
+class _VideoPlayerLoadingState extends State<VideoPlayerLoading> {
+  bool _initialized;
+
+  @override
+  void initState() {
+    super.initState();
+    _initialized = widget.controller.value.initialized;
+    widget.controller.addListener(() {
+      if (!mounted) {
+        return;
+      }
+      final bool controllerInitialized = widget.controller.value.initialized;
+      if (_initialized != controllerInitialized) {
+        setState(() {
+          _initialized = controllerInitialized;
+        });
+      }
+    });
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    if (_initialized) {
+      return new VideoPlayer(widget.controller);
+    }
+    return new Stack(
+      children: <Widget>[
+        new VideoPlayer(widget.controller),
+        const Center(child: const CircularProgressIndicator()),
+      ],
+      fit: StackFit.expand,
+    );
+  }
+}
+
 class VideoPlayPause extends StatefulWidget {
   final VideoPlayerController controller;
 
@@ -132,9 +176,12 @@ class _VideoPlayPauseState extends State<VideoPlayPause> {
 
   @override
   Widget build(BuildContext context) {
-    final List<Widget> children = <Widget>[
+    return new Stack(
+      alignment: Alignment.bottomCenter,
+      fit: StackFit.expand,
+      children: <Widget>[
         new GestureDetector(
-        child: new VideoPlayer(controller),
+          child: new VideoPlayerLoading(controller),
           onTap: () {
             if (!controller.value.initialized) {
               return;
@@ -153,16 +200,7 @@ class _VideoPlayPauseState extends State<VideoPlayPause> {
           },
         ),
         new Center(child: imageFadeAnimation),
-    ];
-
-    if (!controller.value.initialized) {
-      children.add(new Container());
-    }
-
-    return new Stack(
-      alignment: Alignment.bottomCenter,
-      fit: StackFit.passthrough,
-      children: children,
+      ],
     );
   }
 }

examples/flutter_gallery/pubspec.yaml

@@ -8,7 +8,7 @@ dependencies:
   string_scanner: 1.0.2
   url_launcher: 0.4.2+5
   cupertino_icons: 0.1.1
-  video_player: 0.0.5
+  video_player: 0.0.6
 
   # Also update dev/benchmarks/complex_layout/pubspec.yaml
   flutter_gallery_assets: