我有以下代码

func collectionView(collectionView: UICollectionView,didSelectItemAtIndexPath indexPath: NSIndexPath) {
    let person = people[indexPath.item]
 
    let questionController = UIAlertController(title: "What u wanna do?",message: nil,preferredStyle: .Alert)
    questionController.addAction(UIAlertAction(title: "Rename person",style: .Default,handler: {
 
        (action:UIAlertAction!) -> Void in
 
        let ac = UIAlertController(title: "Rename person",preferredStyle: .Alert)
        ac.addTextFieldWithConfigurationHandler(nil)
 
        ac.addAction(UIAlertAction(title: "Cancel",style: .Cancel,handler: nil))
        ac.addAction(UIAlertAction(title: "OK",style: .Default) { [unowned self,ac] _ in
            let newName = ac.textFields![0] as! UITextField
            person.name = newName.text
 
            self.collectionView.reloadData() })
 
        self.presentViewController(ac,animated: true,completion: nil)
 
    }))
 
    questionController.addAction(UIAlertAction(title: "Delete Person",handler: {
 
        (action:UIAlertAction!) -> Void in
 
        println("hello world")
        self.collectionView.deleteItemsAtIndexPaths([indexPath.item])
        self.collectionView.reloadData()
 
    }))
 
    presentViewController(questionController,completion: nil)
}

当我按删除人员时,你好世界工作正常和应用程序崩溃

控制台输出是

hello world
2015-07-18 13:40:14.628 Project10[15888:1274436] -[__NSCFNumber section]:         unrecognized selector sent to instance 0xb000000000000003
2015-07-18 13:40:14.636 Project10[15888:1274436] *** Terminating app due to    uncaught exception 'NSInvalidArgumentException',reason: '-[__NSCFNumber    section]: unrecognized selector sent to instance 0xb000000000000003'

我究竟做错了什么 ？