在加载视图控制器之后加载collectionview的图像视图

Question

所以我正在swift中构建一个应用程序，用户可以在其中上传带有图片的产品。上传效果很好，但我遇到的问题是图片的下载。用户获得所有产品的概览并点击它们，这将向他发送该产品的详细概览。在该概述中，有一个包含所有图像的collectionview(这就是目标(。我的问题是图片加载速度太慢，无法显示在屏幕上。我想知道是否有一个选项可以在函数中提供图像视图并将图像分配给它们，并且在屏幕已经加载后，图片将逐一加载？

这就是我现在加载图像的功能：

func getPictures(imageStrings: [String], imageViews: [UIImageView]){
let storage = Storage.storage();
for index in 0...imageStrings.count - 1 {
let gsReference = storage.reference(forURL: imageStrings[index])
gsReference.getData(maxSize: 15 * 1024 * 1024) { data, error in
if let error = error {
// Uh-oh, an error occurred!
print(error)
return
} else {
DispatchQueue.main.async {
imageViews[index].image = UIImage(data: data!)
}
print(UIImage(data: data!) as Any)
}
}
}
}

这是我的收藏视图处于活动的视图控制器

import MessageUI
import FirebaseStorage
class ProductDetailViewController: UIViewController, MFMailComposeViewControllerDelegate, UINavigationControllerDelegate, UICollectionViewDelegate, UICollectionViewDataSource   {

@IBOutlet var TitleLable: UILabel!
@IBOutlet var PriceLable: UILabel!
@IBOutlet var ProductDate: UILabel!
@IBOutlet var UsernameLable: UILabel!
@IBOutlet var LocationLable: UILabel!
@IBOutlet var Userdate: UILabel!
@IBOutlet var ReserveerButton: UIButton!
@IBOutlet var DescriptionTextView: UITextView!
@IBOutlet var collectionView: UICollectionView!
var titleLable = String()
var priceLable = String()
var productDate = String()
var descriptionLable = String()
var userId = String()
var usernameLable = String()
var locationLable = String()
var userdate = String()
var email = String()
var imageStrings = [String]()
var images = [UIImage]()
var dbhelper = DBHelper()
override func viewDidLoad() {
super.viewDidLoad()
ReserveerButton.layer.cornerRadius = 20
loadUser(id: userId)
TitleLable.text = titleLable
PriceLable.text = priceLable
ProductDate.text = productDate
DescriptionTextView.text = descriptionLable
UsernameLable.text = usernameLable
loadImages()    
// Do any additional setup after loading the view.
}
private func loadUser(id: String){
let dbhelper = DBHelper()
dbhelper.getUserbyUserID(id: id){ success in
if(dbhelper.users[0].Bedrijf != "NULL"){
self.UsernameLable.text = dbhelper.users[0].Bedrijf
} else {
self.UsernameLable.text = dbhelper.users[0].Voornaam + " " + dbhelper.users[0].Familienaam
}
self.Userdate.text = dbhelper.users[0].Added_on
self.LocationLable.text = dbhelper.users[0].Stad
self.email = dbhelper.users[0].Email
}
}
@IBAction func ReserveerProduct(_ sender: Any) {
if !MFMailComposeViewController.canSendMail() {
print("Mail services are not available")
return
}
let composeVC = MFMailComposeViewController()
composeVC.mailComposeDelegate = self
// Configure the fields of the interface.
composeVC.setToRecipients([self.email])
composeVC.setSubject(self.titleLable)
composeVC.setMessageBody("Beste " + self.usernameLable + ", nnIk zou graag het zoekertje " + self.titleLable + " reserveren.  Is dit nog steeds mogelijk? nnMet vriendelijke groet" , isHTML: false)
// Present the view controller modally.
self.present(composeVC, animated: true, completion: nil)
}
func mailComposeController(_ controller: MFMailComposeViewController, didFinishWith result: MFMailComposeResult, error: Error?) {
switch result.rawValue {
case MFMailComposeResult.cancelled.rawValue :
print("Cancelled")
case MFMailComposeResult.failed.rawValue :
print("Failed")
case MFMailComposeResult.saved.rawValue :
print("Saved")
case MFMailComposeResult.sent.rawValue :
print("Sent")
default: break
}
self.dismiss(animated: true, completion: nil)
}
func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
return imageStrings.count
}
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "ImageCollectionViewCell", for: indexPath) as! ImageCollectionViewCell
cell.contentMode = .scaleAspectFill
return cell
}
func loadImages(){
let dbhelper = DBHelper()
//dbhelper.getPictures2(imageStrings: self.imageStrings, imageViews: self.images)
}
}

希望我能最终解决这个问题！亲切问候B.

Answer 1

我想您面临的问题是加载图像后没有更新集合视图。

首先，getPictures(...)方法需要一个UIImageViews数组。但事实上，不能将它们传递给方法，因为它们是在collectionView中动态创建的。相反，您应该在加载图像后返回这些图像。问题是图像是异步加载的。这意味着您需要使用一个完成处理程序。

func getPictures(imageStrings: [String], completionHandler: @escaping (UIImage) -> ()) {
let storage = Storage.storage();
for index in 0...imageStrings.count - 1 {
let gsReference = storage.reference(forURL: imageStrings[index])
gsReference.getData(maxSize: 15 * 1024 * 1024) { data, error in
if let error = error {
// Uh-oh, an error occurred!
print(error)
return
} else {
completionHandler(UIImage(data: data!))
print(UIImage(data: data!) as Any)
}
}
}
}

然后你需要修改你的loadImages()方法：

func loadImages() {
let dbhelper = DBHelper()
dbhelpergetPictures(imageStrings: [""]) { (loadedImage) in
DispatchQueue.main.async {
self.images.append(loadedImage)
self.collectionView.reloadData()
}
}
}

之后，您需要修改collectionView(numberOfItemsInSection(方法，以使显示的单元格数等于加载的图像数：

func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
return images.count
}

最后，您需要在收藏视图中的UIImageViews中实际显示图像：

func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "ImageCollectionViewCell", for: indexPath) as! ImageCollectionViewCell
cell.contentMode = .scaleAspectFill
cell.imageView.image = images[indexPath.row]
return cell
}

如果你对此有任何疑问，请在评论中提问。

(附言：一个善意的建议：看看swift命名惯例(这里有一个很好的风格指南(。除了类之外，所有名称都应该始终以小写字母开头，并且应该描述它们的用途。示例：var TitleLable: UILabel!->var titleLable: UILabel!和：var titleLable = String()->var title = String()这将使您的代码更加易于理解！(