从在线数据库填充 UICollectionView

Question

我正在创建一个简单的聊天应用程序，它有一个加载屏幕，如果用户未登录，则可以转到登录屏幕，如果用户已登录，则可以直接转到他的聊天。聊天记录显示在 UICollectionView 中。当我第一次测试时，我用我在 class 本身声明的虚拟数据填充它，一切正常。现在我在加载屏幕中从在线数据库中获取用户的聊天记录，并将它们存储在一个名为 user_chats 的数组中，该数组在全局声明。

我使用以下代码填充 UICollectionView ：

func collectionView(collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
   // getUserChats()
    return user_chats.count

}

func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell {

let cell = collectionView.dequeueReusableCellWithReuseIdentifier("chat_cell" , forIndexPath: indexPath) as! SingleChat

cell.chatName?.text = user_chats[indexPath.row].chat_partner!.name
cell.chatTextPreview?.text = user_chats[indexPath.row].chat_messages!.last!.text
let profile_pic_URL = NSURL(string : user_chats[indexPath.row].chat_partner!.profile_pic!)
downloadImage(profile_pic_URL!, imageView: cell.chatProfilePic)
cell.chatProfilePic.layer.cornerRadius = 26.5
cell.chatProfilePic.layer.masksToBounds = true

    let dividerLineView: UIView = {
        let view = UIView()
        view.backgroundColor = UIColor(white: 0.5, alpha: 0.5)
        return view
    }()
    dividerLineView.translatesAutoresizingMaskIntoConstraints = false

    cell.addSubview(dividerLineView)
    cell.addConstraints(NSLayoutConstraint.constraintsWithVisualFormat("H:|-1-[v0]|", options: NSLayoutFormatOptions(), metrics: nil, views: ["v0": dividerLineView]))
    cell.addSubview(dividerLineView)
    cell.addConstraints(NSLayoutConstraint.constraintsWithVisualFormat("V:[v0(1)]|", options: NSLayoutFormatOptions(), metrics: nil, views: ["v0": dividerLineView]))
    return cell

}

func collectionView(collectionView: UICollectionView, didSelectItemAtIndexPath indexPath: NSIndexPath) {

    self.performSegueWithIdentifier("showChat", sender: self)
}

override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {

    if (segue.identifier == "showChat") {

        let IndexPaths = self.collectionView!.indexPathsForSelectedItems()!
        let IndexPath = IndexPaths[0] as NSIndexPath
        let vc = segue.destinationViewController as! SingleChatFull

        vc.title = user_chats[IndexPath.row].chat_partner!.name
    }

}

数据获取：

func getUserChats() {
    let scriptUrl = "*****"
    let userID = self.defaults.stringForKey("userId")
    let params = "user_id=" + userID!
    let myUrl = NSURL(string: scriptUrl);
    let request: NSMutableURLRequest = NSMutableURLRequest(URL: myUrl!)
    request.HTTPMethod = "POST"
    let data = params.dataUsingEncoding(NSUTF8StringEncoding)
    request.timeoutInterval = 10
    request.HTTPBody=data
    request.HTTPShouldHandleCookies=false
    UIApplication.sharedApplication().networkActivityIndicatorVisible = true
    let queue:NSOperationQueue = NSOperationQueue()
    NSURLConnection.sendAsynchronousRequest(request, queue: queue, completionHandler:{ (response: NSURLResponse?, data: NSData?, error: NSError?) -> Void in
        do {
            if (data != nil) {
                do {
                    var dataString = String(data: data!, encoding: NSUTF8StringEncoding)
                    var delimiter = "]"
                    var token = dataString!.componentsSeparatedByString(delimiter)
                    dataString = token[0] + "]"
                    print(dataString)
                    let data_fixed = dataString!.dataUsingEncoding(NSUTF8StringEncoding)
                    do {
                        let jsonArray = try NSJSONSerialization.JSONObjectWithData(data_fixed!, options:[])


                        // LOOP THROUGH JSON ARRAY AND FETCH VALUES
                        for anItem in jsonArray as! [Dictionary<String, AnyObject>] {
                            let curr_chat = Chat()
                            if let chatId = anItem["chatId"] as? String {
                                curr_chat.id = chatId
                            }
                            let friend = Friend()
                            let user1id = anItem["user1_id"] as! String
                            let user2id = anItem["user2_id"] as! String
                            if (user1id == userID) {
                                if let user2id = anItem["user2_id"] as? String {
                                    friend.id = user2id
                                }
                                if let user2name = anItem["user2_name"] as? String {
                                    friend.name = user2name
                                }
                                if let user2profilepic = anItem["user2_profile_pic"] as? String {
                                    friend.profile_pic = user2profilepic
                                }
                            }
                            else if (user2id == userID){
                                if let user1id = anItem["user1_id"] as? String {
                                    friend.id = user1id
                                }
                                if let user1name = anItem["user1_name"] as? String {
                                    friend.name = user1name
                                }
                                if let user1profilepic = anItem["user1_profile_pic"] as? String {
                                    friend.profile_pic = user1profilepic
                                }
                            }

                            curr_chat.chat_partner = friend

                            var chat_messages = [Message]()
                            if let dataArray = anItem["message"] as? [String : AnyObject] {
                                for (_, messageDictionary) in dataArray {
                                    if let onemessage = messageDictionary as? [String : AnyObject] {                                        let curr_message = Message()
                                        if let messageid = onemessage["message_id"] as? String {
                                            curr_message.id =  messageid
                                        }
                                        if let messagedate = onemessage["timestamp"] as? String {
                                            let dateFormatter = NSDateFormatter()
                                            dateFormatter.dateFormat = "yyyy-MM-dd HH:mm:ss"
                                            let date = dateFormatter.dateFromString(messagedate)
                                            curr_message.date = date
                                        }
                                        if let messagesender = onemessage["sender"] as? String {

                                            curr_message.sender = messagesender
                                        }
                                        if let messagetext = onemessage["text"] as? String {
                                            curr_message.text = messagetext
                                        }
                                        chat_messages.append(curr_message)
                                    }}
                            }

                            curr_chat.chat_messages = chat_messages
                            user_chats.append(curr_chat)
                        }

                    }
                    catch {
                        print("Error: \(error)")
                    }
                }
//                       NSUserDefaults.standardUserDefaults().setObject(user_chats, forKey: "userChats")

            }
            else {
                dispatch_async(dispatch_get_main_queue(), {
                    let uiAlert = UIAlertController(title: "No Internet Connection", message: "Please check your internet connection.", preferredStyle: UIAlertControllerStyle.Alert)

                    uiAlert.addAction(UIAlertAction(title: "Ok", style: .Default, handler: { action in
                        self.dismissViewControllerAnimated(true, completion:nil)
                    }))
                    self.presentViewController(uiAlert, animated: true, completion: nil)
                })
            }

        } catch _ {
            NSLog("error")
        }

    })
}

问题是集合视图现在总是空的。我做了一些调试并在第一个函数中放置了一个断点，我看到当加载屏幕仍然显示给用户并且甚至还没有加载聊天屏幕时调用了这个方法。我怀疑这是在加载屏幕中从互联网获取数据之前调用的，因此 user_chats 数组的大小为 0。我习惯于使用 Android 和 ListView 其中 ListView 永远不会填充，直到父视图显示在屏幕上，因此我很困惑。 从网上数据库取数据的方法很好，我已经调试了很多，所以问题不存在。

Answer 1

听起来这是一个异步问题。我不确定您的项目是如何设置的，但您需要在返回响应时在集合视图上调用 reloadData()。

Answer 2

在你从服务器接收到返回的数据并更新了集合视图的数据源之后，你需要刷新集合视图（确保你在主线程上，因为它正在修改 UI):

dispatch_async(dispatch_get_main_queue()) {
        self.collectionView.reloadData()
}

编辑：

另外，我不完全确定你是如何设置你的项目的，但是你可以为你的数据获取创建一个委托，所以每次你从服务器取回一些东西时，它都会调用一个委托方法，它有新的消息。您的集合视图控制器将订阅该委托，并且每次调用该方法时都会重新加载您的集合视图。

代表：

protocol ChatsDelegate {
   func didUpdateChats(chatsArray: NSArray)
}

在您的数据获取中：

user_chats.append(cur_chat)
self.delegate.didUpdateChats(user_chats)

在您的 collectionView 控制器中：

class viewController: ChatsDelegate, ... {
...
   func didUpdateChats(chatsArray: NSArray) {
      dispatch_async(dispatch_get_main_queue()) {
         self.collectionView.reloadData()
      }
   }

Answer 3

最好的选择是在您的函数中添加一个 completionHandler，以便在数据为 return and/or 和 async 函数执行完毕时得到通知。下面的代码是带有 completionHandler 的 getUserCharts 函数的截断版本，当数据加载时 returns 为真或假（您可以将其修改为 return 任何内容你希望）。您可以阅读更多关于闭包/完成处理程序 https://developer.apple.com/library/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Closures.html 或 google.

函数

func getUserChats(completionHandler: (loaded: Bool, dataNil: Bool) -> ()) -> (){
        NSURLConnection.sendAsynchronousRequest(request, queue: queue, completionHandler:{ (response: NSURLResponse?, data: NSData?, error: NSError?) -> Void in
            do {
                if (data != nil) {
                    do {
                        var dataString = String(data: data!, encoding: NSUTF8StringEncoding)
                        var delimiter = "]"
                        var token = dataString!.componentsSeparatedByString(delimiter)
                        dataString = token[0] + "]"
                        print(dataString)
                        let data_fixed = dataString!.dataUsingEncoding(NSUTF8StringEncoding)
                        do {
                            let jsonArray = try NSJSONSerialization.JSONObjectWithData(data_fixed!, options:[])

                            // LOOP THROUGH JSON ARRAY AND FETCH VALUES
                            completionHandler(loaded: true, dataNil: false)
                        }
                        catch {
                            print("Error: \(error)")
                        }
                    }
                }
                else {
                    //Handle error or whatever you wish
                    completionHandler(loaded: true, dataNil: true)
                }

            } catch _ {
                NSLog("error")
            }

使用方法

override func viewDidLoad() {
        getUserChats(){
            status in
            if status.loaded == true && status.dataNil == false{
                self.collectionView?.reloadData()
            }
        }
    }

从在线数据库填充 UICollectionView

Populating UICollectionView from Online Database

ios

uicollectionview

swift

ios-lifecycle