increment number using async calls in for loop

code.swift

// get number of files before starting.
var getNumberFull = DealWithFileSystem.fetchNumberOfFilesInFolder(folderName: "Folder2")
for asset in self.arrayOfSelectAssets {
	if let getNumberFromThumb = DealWithFileSystem.fetchNumberOfFilesInFolder(folderName: "Folder1") {
		let filePathThumb = DealWithFileSystem.fetchFolderName(folderName: "Folder1")?.appendingPathComponent("Image \(getNumberFromThumb).png")
		let fetchOption = PHImageRequestOptions()
		fetchOption.isSynchronous = true
		fetchOption.deliveryMode = .highQualityFormat
		PHImageManager.default().requestImage(for: asset, targetSize: CGSize(width:130,height:130), contentMode: .aspectFit, options: fetchOption, resultHandler: { (img, nil) in
			if let convert = UIImagePNGRepresentation(img!) {
				try! convert.write(to: filePathThumb!)
			}
		})
	}
	// increment number before writing (never affected by async call).
	getNumberFull = getNumberFull + 1
	let filePathFull = DealWithFileSystem.fetchFolderName(folderName: "Folder2")?.appendingPathComponent("Image \(getNumberFull!).png")
	let fetchOption = PHImageRequestOptions()
	fetchOption.isSynchronous = true
	PHImageManager.default().requestImageData(for: asset, options: nil, resultHandler: { (data, fetchOption, _, _) in
		try! data?.write(to: filePathFull!)
	})
}