从数组中删除重复的相集?

我正在使用第三方库 BSImagePicker 从照片库中选择多个图像。我可以设置最大值 PHAssets 但当我显示 BSImagePickerController 选择更多照片。那些 相集 只是添加到 selectedAssets 几乎可以复制图像。我试图删除副本 PHAsset 和使用但不起作用的图像:

extension Array where Element: Equatable {
mutating func removeDuplicates() {
    var result = [Element]()
    for value in self {
        if !result.contains(value) {
            result.append(value)
        }
    }
    self = result
   }
}

func presentBSImagePickerController(vc: BSImagePickerViewController) {
        self.bs_presentImagePickerController(vc, animated: true,
                                             select: { (asset: PHAsset) -> Void in

        }, deselect: { (asset: PHAsset) -> Void in
            // User deselected an assets.

        }, cancel: { (assets: [PHAsset]) -> Void in
            // User cancelled. And this where the assets currently selected.

        }, finish: { (assets: [PHAsset]) -> Void in


            // User finished with these assets

            for i in 0..<assets.count  {
                self.selectedAssets.append(assets[i])
            }
            self.selectedAssets.removeDuplicates()

            self.convertAssetToImages()

        }, completion: nil)
    }

    func convertAssetToImages() -> Void {

        if selectedAssets.count != 0 {

            for i in 0..<selectedAssets.count {

                let manager = PHImageManager.default()
                let option = PHImageRequestOptions()
                var thumbnail = UIImage()
                option.isSynchronous = true

                manager.requestImage(for: selectedAssets[i], targetSize: CGSize(width: 200, height: 200), contentMode: .aspectFill, options: option, resultHandler: {(result, info)->Void in
                    thumbnail = result!

                })

                let data = UIImageJPEGRepresentation(thumbnail, 0.7)
                let newImage = UIImage(data: data!)

                self.photosArray.append(newImage! as UIImage)
                self.photosArray.removeDuplicates()
                print(self.photosArray.removeDuplicates())

                DispatchQueue.main.async {
                    self.collectionView.reloadData() // reloads the collection view on main thread
                }
            }
        }
    }