Swift: There is way to debug decodable object quickly

Question

I have an object from 20 fields. When I get the json from the server I get an error about the decode of the json.

There is a way to quickly find out which field is problematic instead of deleting all the fields and putting it back one after the other to find out which one is problematic.

Print the error message (and don't use optional properties unless they really are optional). — Joakim Danielson, Jan 22 '20 at 07:57

score 19 · Answer 1 · answered Sep 30 '20 at 19:22

You can also add additional catch blocks to understand exactly what is the nature of the error.

do {
    let decoder = JSONDecoder()
    let messages = try decoder.decode(Response.self, from: data)
    print(messages as Any)
} catch DecodingError.dataCorrupted(let context) {
    print(context)
} catch DecodingError.keyNotFound(let key, let context) {
    print("Key '\(key)' not found:", context.debugDescription)
    print("codingPath:", context.codingPath)
} catch DecodingError.valueNotFound(let value, let context) {
    print("Value '\(value)' not found:", context.debugDescription)
    print("codingPath:", context.codingPath)
} catch DecodingError.typeMismatch(let type, let context) {
    print("Type '\(type)' mismatch:", context.debugDescription)
    print("codingPath:", context.codingPath)
} catch {
    print("error: ", error)
}

Detailed debugging point, saved my day..Thanks..!! – Sakshi Jul 23 '21 at 14:41 — Sakshi, Jul 23 '21 at 14:41

score 18 · Accepted Answer · answered Jan 22 '20 at 07:58

18

If you're using Codable to parse your JSON, you can simply print the error in catch block and it will print the complete details of where the issue exist.

do {
    let response = try JSONDecoder().decode(Root.self, from: data)
    print(response)
} catch {
    print(error) //here.....
}

answered Jan 22 '20 at 07:58

PGDev

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Then the problem might be with the JSON. It might be invalid. Use https://jsonformatter.org to validate your JSON. – PGDev Jan 22 '20 at 08:00
1

Luv u again! xD – Andres Paladines Aug 14 '21 at 21:33

score 5 · Answer 3 · answered Jan 22 '20 at 07:58

5

Just print the error instance (never error.localizedDescription) in the catch block.

The error displays the CodingPath and the affected key where the error occurs.

answered Jan 22 '20 at 07:58

vadian

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4

Thanks this is my mistake I printed localized description – Mickael Belhassen Jan 22 '20 at 08:05

Swift: There is way to debug decodable object quickly

3 Answers3