Question

我正在尝试构建一个简单的iPhone应用程序，使用UITextView和UIButton将用户输入的文本保存到iCloud。我从来没有这样做过，所以我跟着this tutorial。到目前为止，他们的教程对我来说都是完美无缺的，直到这一次。该应用程序构建良好，并在我的iPhone上运行，显示输入文本的位置，以及用于将文本保存到iCloud的按钮。但是，当我点击屏幕输入文字时，应用程序会崩溃：

2017-03-24 08：45：56.093572 Gaethr2 [6342：1419021] *由于未捕获的异常'NSInvalidArgumentException'而终止应用程序，原因：'* - [NSMetadataQuery valueOfAttribute：forResultAtIndex：]： index（0）越界（0）' ***第一次抛出调用堆栈：（0x184b611b8 0x18359855c 0x184b61100 0x1855f1460 0x100056ffc 0x10005857c 0x184afab10 0x184afa214 0x184af9f90 0x184b69b8c 0x184a3be64 0x185570e0c 0x1855ef268 0x184afab10 0x184afa214 0x184af9f90 0x184b69b8c 0x184a3be64 0x185570e0c 0x1968d93e4 0x1968db29c 0x184b0ea44 0x184b0e240 0x184b0c094 0x184a3a2b8 0x1864ee198 0x18aa817fc 0x18aa7c534 0x10005b720 0x183a1d5b8） libc ++ abi.dylib：以NSException类型的未捕获异常终止来自调试器的消息：无法发送k数据包

这是ViewController代码：

import UIKit

class ViewController: UIViewController
{
    @IBOutlet weak var textView: UITextView!

    var document: MyDocument?
    var documentURL: URL?
    var ubiquityURL: URL?
    var metaDataQuery: NSMetadataQuery?



    func metadataQueryDidFinishGathering(notification: NSNotification) -> Void
    {
        let query: NSMetadataQuery = notification.object as! NSMetadataQuery

        query.disableUpdates()

        NotificationCenter.default.removeObserver(self,
                                                  name: NSNotification.Name.NSMetadataQueryDidFinishGathering,
                                                  object: query)

        query.stop()

        let resultURL = query.value(ofAttribute: NSMetadataItemURLKey,
                                    forResultAt: 0) as! URL

        if query.resultCount == 1 {
            let resultURL = query.value(ofAttribute: NSMetadataItemURLKey,
                                        forResultAt: 0) as! URL

            document = MyDocument(fileURL: resultURL as URL)

            document?.open(completionHandler: {(success: Bool) -> Void in
                if success {
                    print("iCloud file open OK")
                    self.textView.text = self.document?.userText
                    self.ubiquityURL = resultURL as URL
                } else {
                    print("iCloud file open failed")
                }
            })
        } else {
            document = MyDocument(fileURL: ubiquityURL!)

            document?.save(to: ubiquityURL!,
                           for: .forCreating,
                           completionHandler: {(success: Bool) -> Void in
                            if success {
                                print("iCloud create OK")
                            } else {
                                print("iCloud create failed")
                            }
            })
        }
    }



    override func viewDidLoad()
    {
        super.viewDidLoad()

        let filemgr = FileManager.default

        ubiquityURL = filemgr.url(forUbiquityContainerIdentifier: nil)

        guard ubiquityURL != nil else {
            print("Unable to access iCloud Account")
            print("Open the Settings app and enter your Apple ID into iCloud settings")
            return
        }

        ubiquityURL = ubiquityURL?.appendingPathComponent(
            "Documents/savefile.txt")

        metaDataQuery = NSMetadataQuery()

        metaDataQuery?.predicate =
            NSPredicate(format: "%K like 'savefile.txt'",
                        NSMetadataItemFSNameKey)
        metaDataQuery?.searchScopes =
            [NSMetadataQueryUbiquitousDocumentsScope]

        NotificationCenter.default.addObserver(self,
                                               selector: #selector(
                                                ViewController.metadataQueryDidFinishGathering),
                                               name: NSNotification.Name.NSMetadataQueryDidFinishGathering,
                                               object: metaDataQuery!)

        metaDataQuery!.start()
    }

    @IBAction func saveDocument(_ sender: AnyObject)
    {

        document!.userText = textView.text

        document?.save(to: ubiquityURL!,
                       for: .forOverwriting,
                       completionHandler: {(success: Bool) -> Void in
                        if success {
                            print("Save overwrite OK")
                        } else {
                            print("Save overwrite failed")
                        }
        })
    }

    override func didReceiveMemoryWarning()
    {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }


}

这是MyDocument.Swift的代码

import UIKit

class MyDocument: UIDocument
{
    var userText: String? = "Some Sample Text"

    override func contents(forType typeName: String) throws -> Any
    {
        if let content = userText
        {

            let length =
                content.lengthOfBytes(using: String.Encoding.utf8)
            return NSData(bytes:content, length: length)
        }
        else
        {
            return Data()
        }
    }

    override func load(fromContents contents: Any, ofType typeName: String?) throws
    {
        if let userContent = contents as? Data
        {
            userText = NSString(bytes: (contents as AnyObject).bytes,
                                length: userContent.count,
                                encoding: String.Encoding.utf8.rawValue) as? String
        }
    }
}

以下是崩溃的截图：

感谢您的帮助！

Answer 1

未捕获的异常是

- [NSMetadataQuery valueOfAttribute：forResultAtIndex：]：index（0）越界（0）＆＃39;

删除第一次出现的

let resultURL = query.value(ofAttribute: NSMetadataItemURLKey,
                                forResultAt: 0) as! URL

如果query.results为空

，则会造成错误

什么是“未捕获的例外”？

1 个答案: