Swift AnyObject is not convertible to String/Int

问题

I want to parse a JSON to object, but I have no idea how to cast AnyObject to String or Int since I'm getting:

0x106bf1d07:  leaq   0x33130(%rip), %rax       ; "Swift dynamic cast failure"

When using for example:

self.id = reminderJSON["id"] as Int

I have ResponseParser class and inside of it (responseReminders is an Array of AnyObjects, from AFNetworking responseObject):

for reminder in responseReminders {
    let newReminder = Reminder(reminderJSON: reminder)
        ...
}

Then in Reminder class I'm initialising it like this (reminder as AnyObject, but is Dictionary(String, AnyObject)):

var id: Int
var receiver: String

init(reminderJSON: AnyObject) {
    self.id = reminderJSON["id"] as Int
    self.receiver = reminderJSON["send_reminder_to"] as String
}

println(reminderJSON["id"]) result is: Optional(3065522)

How can I downcast AnyObject to String or Int in case like this?

//EDIT

After some tries I come with this solution:

if let id: AnyObject = reminderJSON["id"] { 
    self.id = Int(id as NSNumber) 
}

for Int and

if let tempReceiver: AnyObject = reminderJSON["send_reminder_to"] { 
    self.id = "\(tempReceiver)" 
}

for string

回答1:

In Swift, String and Int are not objects. This is why you are getting the error message. You need to cast to NSString and NSNumber which are objects. Once you have these, they are assignable to variables of the type String and Int.

I recommend the following syntax:

if let id = reminderJSON["id"] as? NSNumber {
    // If we get here, we know "id" exists in the dictionary, and we know that we
    // got the type right. 
    self.id = id 
}

if let receiver = reminderJSON["send_reminder_to"] as? NSString {
    // If we get here, we know "send_reminder_to" exists in the dictionary, and we
    // know we got the type right.
    self.receiver = receiver
}

回答2:

reminderJSON["id"] gives you an AnyObject?, so you cannot cast it to Int You have to unwrap it first.

self.id = reminderJSON["id"]! as Int

if you're sure that id will be present in the JSON.

if id: AnyObject = reminderJSON["id"] {
    self.id = id as Int
}

otherwise

回答3:

Now you just need to import foundation. Swift will convert value type(String,int) into object types(NSString,NSNumber).Since AnyObject works with all objects now compiler will not complaint.

回答4:

This is actually pretty simple, the value can be extracted, casted, and unwrapped in one line: if let s = d["2"] as? String, as in:

var d:[String:AnyObject] = [String:AnyObject]()
d["s"] = NSString(string: "string")

if let s = d["s"] as? String {
    println("Converted NSString to native Swift type")
}

来源：https://stackoverflow.com/questions/25449080/swift-anyobject-is-not-convertible-to-string-int

标签

swift

xcode6-beta6