从url下载图像并存储到Swift中的照片库中

从URL下载图像并显示到表视图中,当我选择图像时,它将存储到照片库中。我已成功从URL获取图像并显示到表视图,但在选择图像后无法将其存储到照片库中。

这是我的代码:

var parsingdata = [Datavalues]()

func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
    let cell = Tableview.dequeueReusableCell(withIdentifier: "cell", for: indexPath) as! CustomTableViewCell
    let row = indexPath.row
    let cellvalues = parsingdata[row] as Datavalues
    cell.CategoryImage.downloadImageFrom(link: cellvalues.categoryImage, contentMode: .scaleToFill)
    cell.categoryName.text = cellvalues.categoryName
    cell.IDLabel.text = String(cellvalues.id)
    return cell
}

func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {

    let indexPath = tableView.indexPathForSelectedRow!

    let imagestring = String(parsingdata[indexPath.row].categoryImage)

//Image add name is stored into the imagestring 

    let documentsDirectoryURL = try! FileManager().url(for: .documentDirectory, in: .userDomainMask, appropriateFor: nil, create: true)
    let fileURL = documentsDirectoryURL.appendingPathComponent("Savedframe.png")
    if !FileManager.default.fileExists(atPath: fileURL.path) {
        do {
            try UIImagePNGRepresentation(imagestring)!.write(to: fileURL)
            print("Image Added Successfully")
        } catch {
            print(error)
        }
    } else {
        print("Image Not Added")
    }
}

我哪里做错了?我的目标是从url下载图像,选择图像后将其存储到照片库中。