demo:add shareVideo

example/lib/main.dart

@@ -47,7 +47,8 @@ class _MyAppState extends State<MyApp> {
 class ShareSelectorPage extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
-    return new Column(
+    return Center(
+      child: new Column(
         children: <Widget>[
           new OutlineButton(onPressed: () {
             Navigator.of(context).pushNamed("shareText");
@@ -63,7 +64,12 @@ class ShareSelectorPage extends StatelessWidget {
             Navigator.of(context).pushNamed("shareMusic");
 
           }, child: const Text("share music")),
+          new OutlineButton(onPressed: () {
+            Navigator.of(context).pushNamed("shareVideo");
+
+          }, child: const Text("share video")),
         ],
+      ),
     );
   }
 }