單獨設置圓角

UIBezierPath *topmaskPath = [UIBezierPath bezierPathWithRoundedRect:topView.bounds byRoundingCorners:UIRectCornerTopLeft | UIRectCornerTopRight cornerRadii:CGSizeMake(10, 10)];
   CAShapeLayer *topmaskLayer = [[CAShapeLayer alloc] init];
   topmaskLayer.frame = topView.bounds;
   topmaskLayer.path = topmaskPath.CGPath;
   topView.layer.mask = topmaskLayer;