Determine “nil” value in JSON

Question

The app receives JSON object from the server. And some field in the object can be missing, or be nil . So, I need to find them before computing a value. I have a code fragment as below:

print(package["store"]!["cover"]) //here, console output: "nil"
if ((package["store"]!["cover"]) != nil) {
    //the 'if' statment above has no effect, statment below is executed,
    // and error occurs.
    imageName = STATIC_IMAGE_URL + (package["cover"] as! String)
}

How can I detect if the response JSON has some missing or nil fields?

Answer 1

You can use optional chaining , optional binding , and conditional casting combined in the same if-let statement:

if let cover = package["store"]?["cover"] as? String {
    imageName = STATIC_IMAGE_URL + cover
} else {
    imageName = "someDefaultImage"
}

It works like this:

• package["store"]?["cover"] will return nil if either package["store"] , or package["store"]["cover"] is nil
• the conditional cast as? String as? String returns nil if the expression to the left is not a String
• finally the if-let construct will either populate cover with the actual string, or will go on the else branch if there's no match