ios风格的按钮
CupertinoButton({
Key key,
@required this.child,
this.padding,
this.color,
this.disabledColor = CupertinoColors.quaternarySystemFill,
this.minSize = kMinInteractiveDimensionCupertino,
this.pressedOpacity = 0.4,
this.borderRadius = const BorderRadius.all(Radius.circular(8.0)),
@required this.onPressed,
})padding: EdgeInsets.fromLTRB(),color: Colors.green,disabledColor: Colors.blue,minSize: 40.0,pressedOpacity: 0.2,borderRadius: BorderRadius.all(Radius.circular(8.0)),onPressed: (){},