实现圆形头像的效果有三种，喜欢哪种用哪种

（1）ClipOval

new ClipOval(
	child:new Image.asset("assets/image/a.png");
)

（2）CircleAvatar

new CircleAvatar (
	radius:30.0,
	backgroundImage:AssetImage("assets/image/a.png"),
)

（3）BoxDecoration BoxShape.circle

Container(
	width:72.0,
	height:72.0,
	decoration:BoxDecoration(
		shape:BoxShape.circle,
		image:DecorationImage(
			image:AssetImage("assets/images/a.png"),
		)
	)
)

效果：

仅供学习使用