Is it possible to save NSData(obtained from NSKeyedArchiver) as NSString and then read back as NSData? - swift

Question

I want to save some information to video metadata. Now I can save the text, that is String object.
// this works well
let metaItem = AVMutableMetadataItem()
metaItem.key = AVMetadataCommonKeySource as NSCopying & NSObjectProtocol
metaItem.keySpace = AVMetadataKeySpaceCommon
metaItem.value = String("some text") as! NSCopying & NSObjectProtocol
So instead of just String I'd like to serialize custom object:
class ARTRMetadata: NSObject, NSCoding {
// ...
required init(coder aDecoder: NSCoder) {
//...
}
func encode(with aCoder: NSCoder) {
//...
}
}
I tried to convert Data to String, it crashed, now I stucked at writing/reading that Data to .txt file:
static func saveMetadataObjectAsText(memento: ARTRMetadata)->String {
let tempFilepath = NSTemporaryDirectory().appending("someFile2.txt")
FileManager.default.createFile(atPath: tempFilepath, contents: nil, attributes: nil)
if NSKeyedArchiver.archiveRootObject(memento, toFile: tempFilepath) {}
else { print("archiveRootObject toFile: FAILURE") }
do {
let contentsFeedToMetadataItem = try String(contentsOfFile: tempFilepath)
//let contentsFeedToMetadataItem = try String(contentsOfFile: tempFilepath, encoding: String.Encoding.utf8) // The file “someFile2.txt” couldn’t be opened using text encoding Unicode (UTF-8).
return contentsFeedToMetadataItem
}
catch { print(error) }
return "ERROR in contentsFeedToMetadataItem"
}
Now it crashes because "The file “someFile2.txt” couldn’t be opened because the text encoding of its contents can’t be determined."
I suppose the problem is that NSData obtained from NSKeyedArchiver is not valid NSString. If I am correct, how to dump the data as text? And then restore it with the same bytes (for NSKeyedUnarchiver)?
Thanks in advance!

Answer 1

Why do you want to save data as text file? Even if you could save Data as string (indeed you can if you encode it with base64) it's not human readable anyway – well there might be a very few people who can read base64 fluently.
Long story short, save Data directly to disk and read it back. Data provides appropriate API.
By the way: archiveRootObject(toFile writes Data anyway, so read try Data(contentsOfFile: tempFilepath) and return that.