ios - "The data couldn’t be read because it is missing" error when decoding JSON in Swift

Question

I am getting the following error :

The data couldn’t be read because it is missing.

When I run the following code:

struct Indicator: Decodable {
    let section: String
    let key: Int
    let indicator: Int
    let threshold: Int
}
    var indicators = [Indicator]()

    do {
        if let file = Bundle.main.url(forResource: "indicators", withExtension: "json") {
            indicators = try JSONDecoder().decode([Indicator].self, from: try Data(contentsOf: file))
        }
    } catch {
        print(error.localizedDescription)
    }

These are in a function, but I have removed them for clarity. I have a code block which is very similar in a different file (I copied this code from there and changed the names essentially) so I'm not sure why it's happening. The json file is valid json and has it's target properly set.

Thanks

Answer 1

Printing error.localizedDescription is misleading because it displays only a quite meaningless generic error message.

So never use localizedDescription in Decodable catch blocks.

In the simple form just

print(error)

It shows the full error including the crucial information debugDescription and context.Decodable errors are very comprehensive.

---

While developing code you could catch each Decodable error separately for example

} catch let DecodingError.dataCorrupted(context) {
    print(context)
} catch let DecodingError.keyNotFound(key, context) {
    print("Key '(key)' not found:", context.debugDescription)
    print("codingPath:", context.codingPath)
} catch let DecodingError.valueNotFound(value, context) {
    print("Value '(value)' not found:", context.debugDescription)
    print("codingPath:", context.codingPath)
} catch let DecodingError.typeMismatch(type, context)  {
    print("Type '(type)' mismatch:", context.debugDescription)
    print("codingPath:", context.codingPath)
} catch {
    print("error: ", error)
}

It shows only the most significant information.