错误：在解包可选值时意外发现nil

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我一直在制作应用程序是Swift但我在TableViewController类中一直出错。我找不到任何方法来解决这个问题，并继续收到此错误：

I have been making an app is Swift but I keep getting an error in my TableViewController class. I could not find any way to fix this and kept getting this error :

override func tableView(tableView: UITableView?, cellForRowAtIndexPath indexPath: NSIndexPath!) -> UITableViewCell! { let cell : TextTableViewCell = tableView!.dequeueReusableCellWithIdentifier("Cell", forIndexPath : indexPath!) as TextTableViewCell let madan : PFObject = self.timeLineData.objectAtIndex(indexPath!.row) as PFObject cell.timestampLabel.alpha = 0 cell.usernameLabel.alpha = 0 cell.madanTextView.alpha = 0 cell.madanTextView.text = madan.objectForKey("content") as String var dateFormatter : NSDateFormatter = NSDateFormatter() dateFormatter.dateFormat = "MM-dd-yyyy HH:mm" cell.timestampLabel.text = dateFormatter.stringFromDate(madan.createdAt) var findSender : PFQuery = PFUser.query() findSender.whereKey("objectId", equalTo: madan.objectForKey("sender").objectId) var i = 1 findSender.findObjectsInBackgroundWithBlock { (objects: [AnyObject]!, error: NSError!) -> Void in if !error { let user : PFUser = (objects as NSArray).lastObject as PFUser // Error here cell.usernameLabel.text = user.username UIView.animateWithDuration(0.5, animations: { cell.timestampLabel.alpha = 1 cell.usernameLabel.alpha = 1 cell.madanTextView.alpha = 1 }) } } return cell }

我找不到任何解决方法。

I cannot find any way to fix this.

推荐答案

看起来像如果对象以 nil 的形式返回。首先检查nil：

It looks as if objects is coming back as nil. First check for nil:

if !error { if let actualObjects = objects { let possibleUser = (actualObjects as NSArray).lastObject as? PFUser if let user = possibleUser { cell.usernameLabel.text = user.username // ... } } }

注意：我将更改为到为？。 lastObject 已经返回一个Optional，所以如果最后一个对象无法转换为PFUser，你也可以继续执行。另外，因为 lastObject 可能返回nil，你还需要检查 nil 。

Note: I changed your as to as?. lastObject is already returning an Optional and so you might as well let the execution continue if the last object cannot be converted to PFUser. Also, because lastObject might return nil, you also need to check that for nil.