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在点击 postVC 上的按钮以加载数据并导航到 guestVC 后，我正在尝试从 Parse 服务器加载数据。它工作正常，在某些时候开始使应用程序崩溃......不知道为什么？我收到了致命错误：在展开可选值时意外发现 nil ......任何和所有方向或帮助将不胜感激。谢谢！

import UIKit
import Parse

var postuuid = [String]()

class postVC: UITableViewController {

//postVC button click function
//clicked username button from post
    @IBAction func usernameBtn_click(sender: AnyObject) {
        let i = sender.layer.valueForKey("index") as! NSIndexPath
        let cell = tableView.cellForRowAtIndexPath(i) as! postCell

        // if user tapped on himself go home, else go guest
        if cell.usernameBtn.titleLabel?.text == PFUser.currentUser()?.username {
            let home = self.storyboard?.instantiateViewControllerWithIdentifier("homeVC") as! homeVC
            self.navigationController?.pushViewController(home, animated: true)    
        } else {
            let guest = self.storyboard?.instantiateViewControllerWithIdentifier("guestVC") as! guestVC
            self.navigationController?.pushViewController(guest, animated: true)
        }  
    } 



// guestVC relevant code
import UIKit
import Parse

var guestname = [String]()

class guestVC: UICollectionViewController {

    var uuidArray = [String]()
    var picArray = [PFFile]()

    // posts loading function
    func loadPosts() {     

            let query = PFQuery(className: "posts")
// app keeps crashing in line below when I try to load data to guestVC
            query.whereKey("username", equalTo: guestname.last!)
            query.limit = self.page
            query.findObjectsInBackgroundWithBlock( { (objects:[PFObject]?, error:NSError?) -> Void in

                if error == nil {

                    self.uuidArray.removeAll(keepCapacity: false)
                    self.picArray.removeAll(keepCapacity: false)

                    for object in objects! {
                        self.uuidArray.append(object.valueForKey("uuid") as! String)
                        self.picArray.append(object.valueForKey("pic") as! PFFile)
                    }

                    self.collectionView?.reloadData()
                } else {
                    print(error!.localizedDescription)
                }
                dispatch_async(dispatch_get_main_queue(), { () -> Void in

                    // code here will be executed as the main queue

                })
            })

    }
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2 回答 2

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您使用大量感叹号来强制解开代码中的可选值，这是一个坏习惯。例如，您可以通过以下方式安全地打开 guestname.last：

guard let lastItem = guestname.last else {
// do something else
return
}
query.whereKey("username", equalTo: lastItem)
于 2016-03-17T03:54:26.573 回答
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在添加或追加之前，检查字典键是否具有有效值。检查 'uuid' 或 'pic' 键是否在字典中具有值。如果它有然后添加/附加。

于 2016-03-17T03:49:09.067 回答