6-17 AppBar 加入底圖或用圖片當標題

return Scaffold(
      appBar: AppBar(
        // title: Text(widget.title),
        title: Image.asset('assets/images/logo.png'),
        flexibleSpace: Image(
          image: AssetImage('assets/images/bg.jpg'),
          fit: BoxFit.cover,
        ),
        backgroundColor: Colors.transparent,
      ),
);