Storing a Custom Transformable Array in Core Data Persistently

Sorry I meant 'class NSObject, NSCoding' in the second last line.

I have managed to find the solution on Youtube. https://www.youtube.com/watch?v=Ema17hA0fGQ

Basically, you would still need to transform the string array into coredata readable data using a ValueTransformer class. Details of how to create it are in the video.

Then, under the inspector of the mediaFile attribute, key in the name of the ValueTransformer class you have just created in the 'Value Transformer Name' field.

I tried the solution in the video and it didn't work for me. I have the following setup in my .xcdatamodeld file

I'm trying to work with an array of strings for the notificationUuids property. I'm transforming the values like this

class AttributedStringToDataTransformer: ValueTransformer {
    
    override func transformedValue(_ value: Any?) -> Any? {
        let boxedData = try! NSKeyedArchiver.archivedData(withRootObject: value!, requiringSecureCoding: true)
        return boxedData
    }
    
    override func reverseTransformedValue(_ value: Any?) -> Any? {
        let typedBlob = value as! Data
        let data = try! NSKeyedUnarchiver.unarchivedObject(ofClasses: [NSString.self], from: typedBlob)
        return (data as! String)
    }
    
}

which is almost exactly like it was in the video. I'm trying to store the notificationUuids as an array of [String] and have everything set up to transform from an NSString to a String but it doesn't work. When an Alarm is stored in Core Data with one notificationUuid, everything works as expected. But when it's got more than one notificationUuid, like in the case that recurrence is set to .daily, then nothing gets saved in the notificationUuids array and when that array is fetched during loading it is empty. Why is this?

Hi Hoid,

Sorry for the late reply.

override func reverseTransformedValue(_ value: Any?) -> Any? {  
        let typedBlob = value as! Data  
        let data = try! NSKeyedUnarchiver.unarchivedObject(ofClasses: [NSString.self], from: typedBlob)  
        return (data as! String)  
    } 

In the above, you declared data to be of class NSString. There could be a conflict when you tried to return String instead of NSString? And you should be returning [String] instead of String if your intention is to store as an array. If you archive it as an array, you should unarchive and return an array.

Try this instead [with usage of unarchivedObject(with:...) method]:

class AttributedStringToDataTransformer: ValueTransformer {  
    override func transformedValue(_ value: Any?) -> Any? {  
        let boxedData = NSKeyedArchiver.archivedData(withRootObject: value!)  
        return boxedData  
    }  
    override func reverseTransformedValue(_ value: Any?) -> Any? {  
        let typedBlob = value as! Data        
        let data = NSKeyedUnarchiver.unarchivedObject(with: typedBlob)  
        return (data as! [String])  
    }  
}