在 UITableView Swift 中重构 cellForRowIndexPath

Question

我有一个相当长的cellForRowAtIndexPath 函数。我使用 parse 作为我的后端并且有很多事情要做。我想提取很多这些条件并将它们放在自己的函数中。尤其是 PFUser 查询，但不幸的是，我不知道最好的方法是什么，因为我不知道如何访问我想要编写的那些函数中每个单元格的元素。

override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {

    let cell = tableView.dequeueReusableCellWithIdentifier("PostCells", forIndexPath: indexPath) as! NewsFeedTableCellTableViewCell

    // Configure the cell...

    // A drive is a post
    let drive: PFObject = self.timelineData[indexPath.row] as PFObject
    var driverId = drive.objectForKey("driver")!.objectId!
    var currentUserObjectId = PFUser.currentUser()!.objectId
    if(driverId != currentUserObjectId){
        cell.requestButton.layer.borderWidth = 1
        cell.requestButton.titleLabel!.font = UIFont.systemFontOfSize(11)
        cell.requestButton.tintColor = UIColor.orangeColor()
        cell.requestButton.layer.borderColor = UIColor.orangeColor().CGColor
        cell.requestButton.setTitle("REQUEST", forState: UIControlState.Normal)

    }
    else {

        cell.requestButton.layer.borderWidth = 1
        cell.requestButton.titleLabel!.font = UIFont.systemFontOfSize(11)
        cell.requestButton.tintColor = UIColor.grayColor()
        cell.requestButton.layer.borderColor = UIColor.lightGrayColor().CGColor
        cell.requestButton.setTitle("REQUEST", forState: UIControlState.Normal)
        cell.requestButton.enabled = false

    }


    // Setting up the attributes of the cell for the news feed
    cell.driveTitleTextField.text = drive.objectForKey("title") as! String
    cell.wayTextField.text = drive.objectForKey("way") as! String

    var departureDate = NSDate()
    departureDate = drive.objectForKey("departureDate") as! NSDate
    var dateFormat = NSDateFormatter()
    dateFormat.dateFormat = "M/dd hh:mm a"
    cell.departureDateTextField.text = dateFormat.stringFromDate(departureDate)

    if((drive.objectForKey("way")!.isEqualToString("Two Way")))
    {
        var returnDate = NSDate()
        returnDate = drive.objectForKey("returnDate") as! NSDate
        cell.returningDateTextField.text = dateFormat.stringFromDate(returnDate)
    }
    else if((drive.objectForKey("way")!.isEqualToString("One Way")))
    {
        cell.returningDateTextField.enabled = false
        cell.returningDateTextField.userInteractionEnabled = false
        cell.returningDateTextField.hidden = true
        cell.returningLabel.hidden = true
    }

    var seatNumber = NSNumber()
    seatNumber = drive.objectForKey("seatNumber") as! NSInteger
    var numberFormat = NSNumberFormatter()
    numberFormat.stringFromNumber(seatNumber)
    cell.seatNumberTextField.text = numberFormat.stringFromNumber(seatNumber)


    // this is a PFUser query so we can get the users image and name and email from the User class 
    var findDrive = PFUser.query()
    var objectId: AnyObject? = drive.objectForKey("driver")!.objectId!
    findDrive?.whereKey("objectId", equalTo: objectId!)
    findDrive?.findObjectsInBackgroundWithBlock{
        (objects:[AnyObject]?, error:NSError?)->Void in
        if (error == nil){
            if let actualObjects = objects {
                let possibleUser = (actualObjects as NSArray).lastObject as? PFUser
                if let user = possibleUser {
                    cell.userProfileNameLabel.text = user["fullName"] as? String
                    cell.userEmailLabel.text = user["username"] as? String

                    //Profile Image
                    cell.profileImage.alpha = 0
                    if let profileImage = user["profilePicture"] as? PFFile {
                        profileImage.getDataInBackgroundWithBlock{
                            (imageData:NSData? , error:NSError?)-> Void in

                            if(error == nil) {
                                if imageData != nil{
                                    let image:UIImage = UIImage (data: imageData!)!
                                    cell.profileImage.image = image
                                }
                            }
                        }

                    }

                    UIView.animateWithDuration(0.5, animations: {
                        cell.driveTitleTextField.alpha = 1
                        cell.wayTextField.alpha = 1
                        cell.profileImage.alpha = 1
                        cell.userProfileNameLabel.alpha = 1
                        cell.userEmailLabel.alpha = 1
                        cell.seatNumberTextField.alpha = 1
                        cell.returningDateTextField.alpha = 1
                        cell.departureDateTextField.alpha = 1

                    })

                }
            }

        }
    }
    return cell
}

编辑 1

我想出了一种重构我的代码的方法，我希望得到批评！

1.我提取了很多单元格配置并将它们放入函数中，一个用于单元格上的按钮，另一个用于解析的所有数据。

func configureDataTableViewCell(cell:NewsFeedTableCellTableViewCell, drive: PFObject)
{
    cell.driveTitleTextField.text = drive.objectForKey("title") as! String
    cell.wayTextField.text = drive.objectForKey("way") as! String
    cell.userEmailLabel.text = drive.objectForKey("username") as? String
    cell.userProfileNameLabel.text = drive.objectForKey("name") as? String

    var departureDate = NSDate()
    departureDate = drive.objectForKey("departureDate") as! NSDate
    var dateFormat = NSDateFormatter()
    dateFormat.dateFormat = "M/dd hh:mm a"
    cell.departureDateTextField.text = dateFormat.stringFromDate(departureDate)

    if((drive.objectForKey("way")!.isEqualToString("Two Way")))
    {
        var returnDate = NSDate()
        returnDate = drive.objectForKey("returnDate") as! NSDate
        cell.returningDateTextField.text = dateFormat.stringFromDate(returnDate)
    }
    else if((drive.objectForKey("way")!.isEqualToString("One Way")))
    {
        cell.returningDateTextField.enabled = false
        cell.returningDateTextField.userInteractionEnabled = false
        cell.returningDateTextField.hidden = true
        cell.returningLabel.hidden = true
    }

    var seatNumber = NSNumber()
    seatNumber = drive.objectForKey("seatNumber") as! NSInteger
    var numberFormat = NSNumberFormatter()
    numberFormat.stringFromNumber(seatNumber)
    cell.seatNumberTextField.text = numberFormat.stringFromNumber(seatNumber)


}

func configureButtonTableViewCell(cell:NewsFeedTableCellTableViewCell, userID: String)
{
    var currentUserObjectId = PFUser.currentUser()!.objectId
    if(userID != currentUserObjectId){
        cell.requestButton.layer.borderWidth = 1
        cell.requestButton.titleLabel!.font = UIFont.systemFontOfSize(11)
        cell.requestButton.tintColor = UIColor.orangeColor()
        cell.requestButton.layer.borderColor = UIColor.orangeColor().CGColor
        cell.requestButton.setTitle("REQUEST", forState: UIControlState.Normal)
        println("orange")
    }
    else {

        cell.requestButton.layer.borderWidth = 1
        cell.requestButton.titleLabel!.font = UIFont.systemFontOfSize(11)
        cell.requestButton.tintColor = UIColor.grayColor()
        cell.requestButton.layer.borderColor = UIColor.lightGrayColor().CGColor
        cell.requestButton.setTitle("REQUEST", forState: UIControlState.Normal)
        cell.requestButton.enabled = false
        println("gray")
    }

}

2.然后我将第 1 步中的函数传入我的cellForRowIndexPath

    // A drive is a post
    let drive: PFObject = self.timelineData[indexPath.row] as PFObject
    var driverId : String = drive.objectForKey("driver")!.objectId!!
    configureButtonTableViewCell(cell, userID: driverId)
    configureDataTableViewCell(cell, drive: drive)

3. 我在保存时将所有 PFUser 数据存储到我的对象中，而不是查询用户类。因此，当他们保存帖子时，我会得到 PFUser.currentUser() 用户名、全名和个人资料图片。

我的负载数据已被修改。我将所有个人资料图片存储在自己的数组中。

func loadData(){


    var findItemData:PFQuery = PFQuery(className:"Posts")

    findItemData.addDescendingOrder("createdAt")

    findItemData.findObjectsInBackgroundWithBlock{
        (objects:[AnyObject]? , error:NSError?) -> Void in
            if error == nil
            {
                self.timelineData.removeAll(keepCapacity: false)
                self.profilePictures.removeAll(keepCapacity: false)
                self.timelineData = objects as! [PFObject]
                for object in objects! {

                    self.profilePictures.append(object.objectForKey("profilePicture") as! PFFile)


                }

                self.newsFeedTableView.reloadData()


            }

    }
}

最后，这是我更新的cellForRowIndexPath

override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {

    var cell = tableView.dequeueReusableCellWithIdentifier("PostCells", forIndexPath: indexPath) as! NewsFeedTableCellTableViewCell

    // Configure the cell...

    // A drive is a post
    let drive: PFObject = self.timelineData[indexPath.row] as PFObject
    var driverId : String = drive.objectForKey("driver")!.objectId!!
    configureButtonTableViewCell(cell, userID: driverId)
    configureDataTableViewCell(cell, drive: drive)
    println(PFUser.currentUser()?.objectForKey("username"))


    if let profileImage = drive["profilePicture"] as? PFFile {
        profileImage.getDataInBackgroundWithBlock{
            (imageData:NSData? , error:NSError?)-> Void in

            if(error == nil) {
                if imageData != nil{
                    let image:UIImage = UIImage (data: imageData!)!
                    cell.profileImage.image = image
                }
            }
        }

    }


    return cell
}

让我知道你们的想法，我想让我的代码更具可读性、速度和内存效率。

Answer 1

您不应该在 cellForRow 中做任何繁重的模型工作。 您当前尝试执行的操作会大大降低您的 UI 速度。

在大多数情况下，您会希望您的模型对象设置好，并在您到达 cellForRow 之前做好准备。

这意味着在 viewDidLoad 等某处执行 Parse 查询，将这些结果保存在一个数组中，并在需要时将它们应用到 cellForRow 中的单元格。这样，当用户滚动时，不会为进入视图的每个新单元格调度新查询。它已经可用了。

除此之外，如果您需要在获取这些项目后对其进行任何更改，您可以这样做，并且即使在用户滚动时也让它们保持不变。

Answer 2

重构，让你有一些数据类型或一组实例变量作为视图模型。避免进行使 cellForRowAtIndexPath 中的单元格发生变异的异步调用。而是让您的数据访问方法发生变异或重新创建视图模型，并在回调结束时将 dispatch_async 发送到主队列。给它一个闭包，告诉你的表视图重新加载数据以及你需要做的任何其他事情来让视图显示新数据。

这里有一段伪代码来描述我的意思：

func loadData() {
    parseQueryWithCallback() { data in
        self.viewModel = doWhateverTransformsAreNeeded(data)
        dispatch_async(dispatch_get_main_queue(), self.tableView.reloadData)
    }
}

func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) {
    let cell = dequeue(...)
    cell.thingOne = self.viewModel.things[indexPath.row].thingOne
    cell.thingTwo = self.viewModel.things[indexPath.row].thingTwo
    return cell
}