ios - 快速的 NSRangeException

Question

大家好，我是 swift 的新手，我的程序面临一个问题。我已在“let defaultStudentId = NSUserDefaults.standardUserDefaults()”中保存一些数据，但每次应用程序停止时。 defaultStudentId.objectForKey("studentId") 这个“studentId”来自另一个 ViewController....我需要帮助这是我的代码和错误......

import UIKit

class OTPViewController: ViewController {

    @IBOutlet weak var OTP_code: UITextField!
    let defaultStudentId = NSUserDefaults.standardUserDefaults()
    override func viewDidLoad() {
        super.viewDidLoad()

    }


    @IBAction func confirm(sender: AnyObject) {

        let std_id = defaultStudentId.objectForKey("studentId")
        let sendOTPCode = "StudentId=\(std_id)&CODE=\(self.OTP_code.text)&PartnerID=4B67B239CF3735814C063DB89D750481"
        let url = NSURL(string: "http://serviceforonair.examonair.com/AndroidService.asmx/VerifyOTPAndActivateStudent")
        let request = NSMutableURLRequest(URL: url!)
        request.HTTPMethod = "POST"
        request.setValue("application/x-www-form-urlencoded", forHTTPHeaderField: "Content-Type")
        request.HTTPBody = sendOTPCode.dataUsingEncoding(NSUTF8StringEncoding)
        let task = NSURLSession.sharedSession().dataTaskWithRequest(request){data, response, error in
            if error != nil{
                print(error)
                return
            }
            do{
                let responseString = NSString(data: data!, encoding: NSUTF8StringEncoding)
                var message : String!
                message = responseString?.stringByReplacingCharactersInRange(NSMakeRange(0, 76), withString: "").stringByReplacingOccurrencesOfString("</string>", withString: "")
                print(self.defaultStudentId)

            }
            catch let jsonException{
                print(jsonException)
            }
        }
        task.resume()



    }
}

错误2016-08-15 20:14:10.555 DBMCI [21415:143621] * 由于未捕获的异常“NSRangeException”而终止应用程序，原因:“-[__NSCFString ReplaceCharactersInRange:withString:]:范围或索引超出范围”* 首先抛出调用堆栈:( 0 CoreFoundation 0x000000010dcedd85 异常预处理 + 165 1 libobjc.A.dylib 0x0000000110159deb objc_异常_抛出 + 48 2 CoreFoundation 0x000000010dcedcbd +[NSException 引发:格式:] + 205 3 CoreFoundation 0x000000010dcb90ad mutateError + 221 4 基础 0x000000010e7c887c -[NSString stringByReplacingCharactersInRange:withString:] + 142 5 DBMCI 0x000000010d62de96 _TFFC5DBMCI17OTPViewController7confirmFPs9AnyObject_T_U_FTGSqCSo6NSData_GSqCSo13NSURLResponse_GSqCSo7NSError__T_ + 902 6 DBMCI 0x000000010d622c87 _TTRXFo_oGSqCSo6NSData_oGSqCSo13NSURLResponse_oGSqCSo7NSError__dT__XFdCb_dGSqS__dGSqS0__dGSqS1___dT + 103 7 CFNetwork 0x0000000111118b49 75-[__NSURLSessionLocal taskForClass:request:uploadFile:bodyData:completion:]_block_invoke + 19 8 CFNetwork 0x000000011112b0f2 __49-[__NSCFLocalSessionTask _task_onqueue_didFinish]_block_invoke + 302 9 基础 0x000000010e82f630 __NSBLOCKOPERATION_IS_CALLING_OUT_TO_A_BLOCK + 7 10 基础 0x000000010e76a805 -[NSBlockOperation main] + 101 11 基础 0x000000010e74d725 -[__NSOperationInternal _start:] + 646 12 基础 0x000000010e74d336 __NSOQSchedule_f + 194 13 libdispatch.dylib 0x000000011197a3eb _dispatch_client_callout + 8 14 libdispatch.dylib 0x000000011196082c _dispatch_queue_drain + 2215 15 libdispatch.dylib 0x000000011195fd4d _dispatch_queue_invoke + 601 16 libdispatch.dylib 0x0000000111962996 _dispatch_root_queue_drain + 1420 17 libdispatch.dylib 0x0000000111962405 _dispatch_worker_thread3 + 111 18 libsystem_pthread.dylib 0x0000000111cb74de _pthread_wqthread + 1129 19 libsystem_pthread.dylib 0x0000000111cb5341 start_wqthread + 13)libc++abi.dylib:以 NSException 类型的未捕获异常终止(lldb)

Answer 1

基本上

let std_id = defaultStudentId.objectForKey("studentId")

返回一个可选值，因此在字符串插值中“StudentId=\(std_id)”您将得到例如“StudentId=Optional(24)”而不是预期的 "StudentId=24" 这肯定不是您想要的。

假设键 studentId 的对象是一个 String 将上面的行替换为

guard let std_id = defaultStudentId.stringForKey("studentId") else { return }

它检查 key 的值是否存在，并在成功时解包可选值，否则退出该方法。

崩溃的错误信息与该行相关

message = responseString?.stringByReplacingCharactersInRange(NSMakeRange(0, 76), withString: "").stringByReplacingOccurrencesOfString("</string>", withString: "")

避免硬编码范围长度，而是计算它。如果不能，请检查字符串的长度。