部分圆角

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