将小部件树包装在SingleChildScrollView中
body: SingleChildScrollView(child: Stack( children: <Widget>[ new Container( decoration: BoxDecoration( image: DecorationImage(...), new Column(children: [ new Container(...), new Container(...... ), new Padding( child: SizedBox( child: RaisedButton(..), ),....... ); // Single child scroll view
请记住，SingleChildScrollView只能有一个直接小部件（就像Android中的ScrollView）
