      *  rotationRadius表示旋转的半径
      *  @warning 仅当 style 为 QMUICollectionViewPagingLayoutStyleRotation 时才生效
      */
+    private var _rotationRatio: CGFloat = 0
     public var rotationRatio: CGFloat {
         get {
-            return validated(rotationRatio: self.rotationRatio)
+            return validated(rotationRatio: _rotationRatio)
         }
         set {
-            self.rotationRatio = newValue
+            _rotationRatio = newValue
         }
     }
 

                    attribute.center.x
                let degress = -90 * self.rotationRatio * (distance / (self.collectionView?.bounds.width ?? 1))

                let cosValue = CGFloat(fabs(cosf(Float(AngleWithDegrees(degress)))))
                let translateY = self.rotationRadius - self.rotationRadius * cosValue
                var transform = CGAffineTransform(translationX: 0, y: translateY)
                transform = transform.rotated(by: AngleWithDegrees(degress))

            return true
        }

        guard let notNilCollectionView = collectionView else {
            return true
        }
        return !notNilCollectionView.bounds.size.equalTo(newBounds.size)
    }

    override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
