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I am trying to save data via a codable protocol. It is an array of structures with structs inside. There are strings, images and bool values and I am thinking it is one of these data types that does not conform to the protocol.

Here is a pic of all the data I must save:
original

struct Checklist 

 var name: String
 var image: UIImage?
 var items: [Item] = 


struct Item 

 var nameOfNote: String
 var remind: Bool
 //var date: Date


struct alldata: Codable 

 var checklists: [Checklist] = 

I have tried to include the protocol in all the structs but it also produced an error. Here's a pic:
tried a solution picture

JSON in Swift 4 is fun (repeat this at 2am in the morning ;)).

One of the first things I always do is consult a good blog, like Ultimate Guide to JSON Parsing with Swift 4. While it might not answer the "direct" question, it will provide a lot of useful information.

Another thing to do, is consult the Apple documentation. In this, a quick look at the documentation for UIImage will point out that it does not conform to Codable, so that's a problem.

Another issue is, JSON doesn't support binary data, it's a text based solution.

This means that you need to figure out away to convert the binary image data to text. Lucky for us, people have already thought about this and the most common mechanism is to use Base 64 encoding.

A quick google search will turn up any number of solutions for encoding/decoding a UIImage to/from base 64, for example Convert between UIImage and Base64 string

Now, we just need to customise the encoding and decoding process.

The first thing is to make sure all the other fields/objects/data we use are also conform to Codable...

struct Item: Codable 
 var nameOfNote: String
 var remind: Bool
 //var date: Date

Then we can set out customising the encoding and decoding process for the image, maybe something like...

struct Checklist: Codable 

 enum CodingKeys: String, CodingKey 
 case image
 case name
 case items
 

 var name: String
 var image: UIImage?
 var items: [Item] = 

 init(from decoder: Decoder) throws 
 let container = try decoder.container(keyedBy: CodingKeys.self)
 name = try container.decode(String.self, forKey: .name)
 items = try container.decode([Item].self, forKey: .items)

 if let text = try container.decodeIfPresent(String.self, forKey: .image) 
 if let data = Data(base64Encoded: text) 
 image = UIImage(data: data)
 
 
 

 func encode(to encoder: Encoder) throws 
 var container = encoder.container(keyedBy: CodingKeys.self)

 if let image = image, let data = image.pngData() 
 try container.encode(data, forKey: .image)
 
 try container.encode(name, forKey: .name)
 try container.encode(items, forKey: .items)
 

nb: This is the basic process I've used for a couple of projects, I've not tested the above myself, but it should present the basic idea you need to get started