In my application, I download a JSON file off of the internet and fill up a UITableView with items from the file. It does work well, and there are no problems or errors, but the scrolling performance is very laggy, and the UI glitches out a tiny bit.
在我的应用程序中，我从Internet上下载了一个JSON文件，并用文件中的项填充UITableView。它确实运行良好，并且没有任何问题或错误，但滚动性能非常滞后，并且UI出现了一点点故障。
I assume this is because of the images that I'm downloading from the JSON file, so I've looked into multi-threading, but I don't think I am doing it right because it does load much faster, but scrolling performance is still the same as before.
我认为这是因为我正在从JSON文件下载的图像，所以我研究了多线程，但我不认为我做得对，因为它的加载速度要快得多，但滚动性能是仍然和以前一样。
Can somebody please tell me how to fix this? This UITableView is the most important thing in the app, and I have been spending much time on trying to fix it. Thank you!
有人可以告诉我如何解决这个问题吗？这个UITableView是应用程序中最重要的东西，我花了很多时间试图修复它。谢谢！
Here is my code-
这是我的代码 -
import UIKit
class ViewController: UIViewController, UITableViewDataSource {
@IBOutlet weak var tableView: UITableView!
var nameArray = [String]()
var idArray = [String]()
var ageArray = [String]()
var genderArray = [String]()
var descriptionArray = [String]()
var imgURLArray = [String]()
let myActivityIndicator = UIActivityIndicatorView(activityIndicatorStyle: UIActivityIndicatorViewStyle.gray)
final let urlString = "https://pbsocfilestorage.000webhostapp.com/jsonDogs.json"
override func viewDidLoad() {
super.viewDidLoad()
self.downloadJsonWithURL()
// Activity Indicator
myActivityIndicator.center = view.center
myActivityIndicator.hidesWhenStopped = true
myActivityIndicator.startAnimating()
view.addSubview(myActivityIndicator)
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
func downloadJsonWithURL() {
let url = NSURL(string:urlString)
URLSession.shared.dataTask(with: (url as? URL)!, completionHandler: {(data, response, error) ->
Void in
print("Good so far...")
if let jsonObj = try? JSONSerialization.jsonObject(with: data!, options: .allowFragments) as? NSDictionary {
print(jsonObj!.value(forKey: "dogs"))
if let dogArray = jsonObj!.value(forKey: "dogs") as? NSArray {
print("Why u no work!")
for dog in dogArray {
if let dogDict = dog as? NSDictionary {
if let name = dogDict.value(forKey: "name") {
self.nameArray.append(name as! String)
}
if let name = dogDict.value(forKey: "id") {
self.idArray.append(name as! String)
}
if let name = dogDict.value(forKey: "age") {
self.ageArray.append(name as! String)
}
if let name = dogDict.value(forKey: "gender") {
self.genderArray.append(name as! String)
}
if let name = dogDict.value(forKey: "image") {
self.imgURLArray.append(name as! String)
}
if let name = dogDict.value(forKey: "description") {
self.descriptionArray.append(name as! String)
}
OperationQueue.main.addOperation ({
self.myActivityIndicator.stopAnimating()
self.tableView.reloadData()
})
}
}
}
}
}).resume()
}
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return nameArray.count
}
func tableView(tableView: UITableView, estimatedHeightForRowAtIndexPath indexPath: NSIndexPath) -> CGFloat {
return UITableViewAutomaticDimension;
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let imgURL = NSURL(string: imgURLArray[indexPath.row])
let cell = tableView.dequeueReusableCell(withIdentifier: "reusableCell") as! TableViewCell
URLSession.shared.dataTask(with: (imgURL as! URL), completionHandler: {(data, resp, error) -> Void in
if (error == nil && data != nil) {
OperationQueue.main.addOperation({
cell.dogNameLabel.text = self.nameArray[indexPath.row]
cell.idLabel.text = self.idArray[indexPath.row]
cell.ageLabel.text = self.ageArray[indexPath.row]
cell.genderLabel.text = self.genderArray[indexPath.row]
print("Cell info was filled in!")
if imgURL != nil {
let data = NSData(contentsOf: (imgURL as? URL)!)
cell.dogImage.image = UIImage(data: data as! Data)
}
})
}
}).resume()
return cell
}
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
if segue.identifier == "showDog" {
if let indexPath = self.tableView.indexPathForSelectedRow{
let detailViewController = segue.destination as! DetailViewController
detailViewController.imageString = imgURLArray[indexPath.row]
detailViewController.nameString = nameArray[indexPath.row]
detailViewController.idString = idArray[indexPath.row]
detailViewController.ageString = ageArray[indexPath.row]
detailViewController.descriptionString = descriptionArray[indexPath.row]
detailViewController.genderString = genderArray[indexPath.row]
}
}
}
}
1 个解决方案
#1
1
There is a big mistake. You are loading data with dataTask but you aren't using that returned data at all. Rather than you are loading the data a second time with synchronous contentsOf. Don't do that.
有一个很大的错误。您正在使用dataTask加载数据，但您根本没有使用返回的数据。而不是您使用同步contentsOf第二次加载数据。不要那样做。
And don't update the labels in the asynchronous completion block. The strings are not related to the image data.
并且不要更新异步完成块中的标签。字符串与图像数据无关。
This is more efficient:
这更有效：
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let imgURL = URL(string: imgURLArray[indexPath.row])
let cell = tableView.dequeueReusableCell(withIdentifier: "reusableCell", for: indexPath) as! TableViewCell
cell.dogNameLabel.text = self.nameArray[indexPath.row]
cell.idLabel.text = self.idArray[indexPath.row]
cell.ageLabel.text = self.ageArray[indexPath.row]
cell.genderLabel.text = self.genderArray[indexPath.row]
print("Cell info was filled in!")
URLSession.shared.dataTask(with: imgURL!) { (data, resp, error) in
if let data = data {
OperationQueue.main.addOperation({
cell.dogImage.image = UIImage(data: data)
})
}
}.resume()
return cell
}
Note: You are strongly discouraged from using multiple arrays as data source. It's very error-prone. Use a custom struct or class. And create imgURLArray with URL instances rather than strings. This is also much more efficient.
注意：强烈建议您不要将多个数组用作数据源。这很容易出错。使用自定义结构或类。并使用URL实例而不是字符串创建imgURLArray。这也更有效率。
Nevertheless you should use a download manager which caches the images and cancels downloads if a cell goes off-screen. At the moment each image is downloaded again when the user scrolls and cellFoRow is called again for this particular cell.
不过你应该使用一个下载管理器来缓存图像，如果一个单元离开屏幕就取消下载。此时，当用户滚动时再次下载每个图像，并再次为该特定单元调用cellFoRow。
#1
1
There is a big mistake. You are loading data with dataTask but you aren't using that returned data at all. Rather than you are loading the data a second time with synchronous contentsOf. Don't do that.
有一个很大的错误。您正在使用dataTask加载数据，但您根本没有使用返回的数据。而不是您使用同步contentsOf第二次加载数据。不要那样做。
And don't update the labels in the asynchronous completion block. The strings are not related to the image data.
并且不要更新异步完成块中的标签。字符串与图像数据无关。
This is more efficient:
这更有效：
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let imgURL = URL(string: imgURLArray[indexPath.row])
let cell = tableView.dequeueReusableCell(withIdentifier: "reusableCell", for: indexPath) as! TableViewCell
cell.dogNameLabel.text = self.nameArray[indexPath.row]
cell.idLabel.text = self.idArray[indexPath.row]
cell.ageLabel.text = self.ageArray[indexPath.row]
cell.genderLabel.text = self.genderArray[indexPath.row]
print("Cell info was filled in!")
URLSession.shared.dataTask(with: imgURL!) { (data, resp, error) in
if let data = data {
OperationQueue.main.addOperation({
cell.dogImage.image = UIImage(data: data)
})
}
}.resume()
return cell
}
Note: You are strongly discouraged from using multiple arrays as data source. It's very error-prone. Use a custom struct or class. And create imgURLArray with URL instances rather than strings. This is also much more efficient.
注意：强烈建议您不要将多个数组用作数据源。这很容易出错。使用自定义结构或类。并使用URL实例而不是字符串创建imgURLArray。这也更有效率。
Nevertheless you should use a download manager which caches the images and cancels downloads if a cell goes off-screen. At the moment each image is downloaded again when the user scrolls and cellFoRow is called again for this particular cell.
不过你应该使用一个下载管理器来缓存图像，如果一个单元离开屏幕就取消下载。此时，当用户滚动时再次下载每个图像，并再次为该特定单元调用cellFoRow。