为什么我收到错误：致命错误：在展开可选值时意外发现 nil？

Question

下面有一个 TableViewController，我试图用 Parse 的查询请求填充它。这个想法是调用（我已经检查并返回必要的信息）然后填充数组，然后我用它来填充 TableViewCells。这些单元格还有一个自定义类（'TableViewCell'）。

出于某种原因，'self.tableView.reloadData()' 肯定会导致崩溃。当我删除它时，它不会崩溃，但 tableviewcells 不会更新解析信息。有什么想法吗？

 import UIKit
 import Parse

 class AuctionViewController: UITableViewController {

override func viewDidLoad() {
    super.viewDidLoad()

    self.tableView.registerClass(TableViewCell.self, forCellReuseIdentifier: "Cell")


} 

var capArray = [String]()
var imageDic = [String: [PFFile]]()
var priceArray = [Int]()


override func viewDidAppear(animated: Bool) {

    capArray.removeAll(keepCapacity: true)
    imageDic.removeAll(keepCapacity: true)
    priceArray.removeAll(keepCapacity: true)

    let query = PFQuery(className: "SellerObject")
    query.findObjectsInBackgroundWithBlock { (objects, error) -> Void in

        if let objects = objects {
            for o in objects {
                if o.objectForKey("caption") != nil && o.objectForKey("imageFile") != nil && o.objectForKey("price") != nil {
                let cap = o.objectForKey("caption") as? String
                    self.capArray.append(cap!)
                let imdic = o.objectForKey("imageFile") as? [PFFile]
                self.imageDic[cap!] = imdic
                let price = o.objectForKey("price") as? String
                let priceInt = Int(price!)
                self.priceArray.append(priceInt!)
                print(self.capArray)
                print(self.imageDic)
                print(self.priceArray)

            }
                self.tableView.reloadData()
            }

        }

    }


}


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

// MARK: - Table view data source

override func numberOfSectionsInTableView(tableView: UITableView) -> Int {
    // #warning Incomplete implementation, return the number of sections
    return 1
}

override func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
    // #warning Incomplete implementation, return the number of rows
    return capArray.count
}


override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
    let cell = tableView.dequeueReusableCellWithIdentifier("Cell", forIndexPath: indexPath) as! TableViewCell

    cell.captionLabel.text = self.capArray[indexPath.row]
    return cell
}

Answer 1

首先，您没有按类型检查 cap、imdic、price。并在循环中多次重新加载 tableView。替换

for o in objects {
            if o.objectForKey("caption") != nil && o.objectForKey("imageFile") != nil && o.objectForKey("price") != nil {
            let cap = o.objectForKey("caption") as? String
                self.capArray.append(cap!)
            let imdic = o.objectForKey("imageFile") as? [PFFile]
            self.imageDic[cap!] = imdic
            let price = o.objectForKey("price") as? String
            let priceInt = Int(price!)
            self.priceArray.append(priceInt!)
            print(self.capArray)
            print(self.imageDic)
            print(self.priceArray)

        }
            self.tableView.reloadData()
        }

与

for o in objects {
           if let cap = o.objectForKey("caption") as? String,
           let imdic = o.objectForKey("imageFile") as? [PFFile],
           let priceInt = (o.objectForKey("price") as? String).flatMap({ Int($0))}) {
              self.capArray.append(cap)
              self.imageDic[cap] = imdic
              self.priceArray.append(priceInt)
              print(self.capArray)
              print(self.imageDic)
              print(self.priceArray)
           }
        }
self.tableView.reloadData()

另外，不要以这种方式使单元格出队。替换

override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
      let cell = tableView.dequeueReusableCellWithIdentifier("Cell", forIndexPath: indexPath) as! TableViewCell

      cell.captionLabel.text = self.capArray[indexPath.row]
      return cell
}

与

override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
    guard let cell = tableView.dequeueReusableCellWithIdentifier("Cell", forIndexPath: indexPath) as? TableViewCell else {
        assertionFailure("cell for index-path:\(indexPath) not found")
        return UITableViewCell()
    }

    cell.captionLabel.text = self.capArray[indexPath.row]
    return cell
}

但我认为问题总是在 TableViewCell 类中? 例如，captionLabel 可能是 nil。