Swift : Use of unresolved identifier 'json'

问题

I'm currently developing my first iOS app using Swift 2.0 and Xcode 7.0.1.

I'm getting a strange little error that I can't seem to fix:

        var err: NSError?

The original code:

        //var json = NSJSONSerialization.JSONObjectWithData(data, options: .MutableContainers, error: &err) as? NSDictionary

Swift2 rewrite code:

        do {
            if let json = try NSJSONSerialization.JSONObjectWithData(data!, options: []) as? NSDictionary {
                print(json)
            }
        } catch {
            print(error)
        }

Use of unresolved identifier 'json' before rewriting

        if let parseJSON = json {
            var resultValue = parseJSON["status"] as? String
            print("result: \(resultValue)")

            var isUserRegistered:Bool = false;
            if(resultValue=="Success") { isUserRegistered = true; }

            var messageToDisplay:String = parseJSON["message"] as! String!;
            if(!isUserRegistered)
            {
                messageToDisplay = parseJSON["message"] as! String!;
            }

            dispatch_async(dispatch_get_main_queue(),{

                //Display alert message with confirmation.
                var myAlert = UIAlertController(title:"Alert", message:messageToDisplay, preferredStyle: UIAlertControllerStyle.Alert);

                let okAction = UIAlertAction(title:"Ok", style:UIAlertActionStyle.Default){ action in
                    self.dismissViewControllerAnimated(true, completion: nil);
                }

                myAlert.addAction(okAction);
                self.presentViewController(myAlert, animated:true, completion:nil);
            });  
        }

The error is thrown at this line:

            if let parseJSON = json {

Can someone please tell me what I'm doing wrong here?

回答1:

the variable json is visible only in the scope of the do block.

Move the code into the do block.
Optional bindings is not needed, too. If the code passes the try statement, parseJSON is valid and non-optional.

do {
   let parseJSON = try NSJSONSerialization.JSONObjectWithData(data!, options: []) as! NSDictionary {
   print(parseJSON)
   var resultValue = parseJSON["status"] as? String
   print("result: \(resultValue)")

   var isUserRegistered:Bool = false;
   if(resultValue=="Success") { isUserRegistered = true; }

   var messageToDisplay:String = parseJSON["message"] as! String!;
   if(!isUserRegistered)
   {
      messageToDisplay = parseJSON["message"] as! String!;
   }

   dispatch_async(dispatch_get_main_queue(),{

      //Display alert message with confirmation.
      var myAlert = UIAlertController(title:"Alert", message:messageToDisplay, preferredStyle: UIAlertControllerStyle.Alert);

      let okAction = UIAlertAction(title:"Ok", style:UIAlertActionStyle.Default){ action in
          self.dismissViewControllerAnimated(true, completion: nil);
       }

       myAlert.addAction(okAction);
       self.presentViewController(myAlert, animated:true, completion:nil);
   });  

} catch let error as NSError {
    print(error)
}

来源：https://stackoverflow.com/questions/33253340/swift-use-of-unresolved-identifier-json

标签

ios

swift2