致命错误：使用字典为有效JSON展开可选值时意外发现nil

Question

As the title states, I am receiving the "fatal error: unexpectedly found nil while unwrapping an Optional value" error. My JSON is valid, and the link can be found here: http://www.mocky.io/v2/5844d2801100001d140e6b91 .

The line of code that is giving me an issue is here:

let fighterDetails = dictionary["Fighters"]! as! [[String:AnyObject]]

At one point, I had all working code. I went back and re-structed my entire code as I decided to change the topic. I fixed all other errors, but I'm left with this at run-time.

Answer 1

When parsing remote JSON data, you should never use the ! operator. Instead, use guard statements when unwrapping:

guard let fighterDetails = dictionary["Fighters"] as? [[String:AnyObject]] else {
    return []
}

And use try? instead of try! .

For the client developer, I recommend the usage of SwiftLint to help you use better Swift practices. It would have detected the issue with as! .

For the server developer, I recommend to stick to one lettercase convention. People tend to recommend camelCase when dealing with JSON keys . ie, you should rename "Fighters" to "fighters" to align with "name", "country", ... It may have avoided the issue of your missing key.

Answer 2

我检查了json网址，那里没有键“ Fighters”。