How do I get the error message in Swift 2.0?

Question

I used this method very much in Swift 1.2: NSURLConnection.sendSynchronousRequest(:_:_:_) but this is apparently deprecated in iOS9. It still works however but now it uses the new Swift 2.0 Error Handling and I don't know how I will get the error message if it fails, ex. if time runs out.

I know I have to put it into a do-catch and then say try before the metho but I dont know how to catch the error message.

do {
    let data = try NSURLConnection.sendSynchronousRequest(request, returningResponse: nil)
    return data 
}
catch _ {
    return nil
}

Before I used NSError and then its description property, but now I have no clue.

Answer 1

Use automatic error variable, and you can cast it to NSError if you wish:

catch {
    let nsError = error as NSError
    print(nsError.localizedDescription)
}

Answer 2

You can now throw any object inheriting ErrorType , and provide custom handling in the catch sentence. You can also cast the error to NSError to access localizedDescription for handling third party errors.

Casting an enum ErrorType will produce a NSError with domain equal to the enum name, code equal to the enum value and an auto-generated localizedDescription with the following format:

The operation couldn't be completed. (DOMAIN error CODE.)

For example, the following code:

enum AwfulError: ErrorType {
    case Bad
    case Worse
    case Terrible
}

func throwingFunction() throws {
    throw AwfulError.Worse
}

do {
    try throwingFunction()
}
catch AwfulError.Bad {
    print("Bad error")
}
catch let error as NSError {
    print(error.localizedDescription)
}

Will print

The operation couldn't be completed. (AwfulError error 1.)

Answer 3

Despite the question title specifying Swift 2, this answer is for Swift 3.

As @redent84 points out, since Swift 2 an Error object may be a home-made one. Here's a method I wrote to analyze and print the default error object available in a "catch" statement that doesn't specify any specific error type:

   // Method to print an unknown Error type object to the system output.
   static func printCaughtError(_ unknownError : Error) {
      let objectDescription = String(describing: unknownError)
      let localizedDescription = unknownError.localizedDescription
      if localizedDescription != "" {
         if localizedDescription.contains(objectDescription) {
            print(localizedDescription)
            return
         }
         if !objectDescription.contains(localizedDescription) {
            print(objectDescription + ": " + localizedDescription)
            return
         }
      }
      print(objectDescription)
   }

Then you can call it like this:

    catch {
       printCaughtError(error)
    }

Answer 4

如何获取userInfo 中的错误消息：

let errorMessage = (error as NSError).userInfo["message"] as? String