ios中如何对view画圆角

UIBezierPath *maskPath = [UIBezierPath bezierPathWithRoundedRect:_view2.bounds byRoundingCorners:UIRectCornerTopLeft|UIRectCornerTopRight cornerRadii:CGSizeMake(20, 20)];

    CAShapeLayer *maskLayer = [[CAShapeLayer alloc] init];

    maskLayer.frame = _view2.bounds;

    maskLayer.path = maskPath.CGPath;

    _view2.layer.mask = maskLayer;

以上方法来自http://webfrogs.me/2013/05/22/ios-view-assign-corner-radius/