Struct v Class - TableView Hidden Data-CodePudding

I have run into a problem in my code and I am new so I am learning as I go (so please be lenient!). Essentially, I have a tableView that shows data when the user adds them. For example, a user adds his weight on multiple days and it shows. I found out that if I use a struct for 'Log', it only shows one tableview cell with one piece of data. HOWEVER, when I use a class for 'Log', it shows all the data. Is this the case in general? I wrote the code for the tableview initially as a 'class Log' but need to change it to a struct and I am encountering this problem. I hope the code is easy to read! Could someone let me know how I could improve my code / give me any pointers? Thank you!

struct Log {
    var title: String
    var Diary: [Diary]
    init(title: String, Diary: [Diary]) {
        self.title = title
        self.Diary = Diary
    }
}
 
struct Diary {
    
    var id: String?
    var Weight: String
    var Body: String
    var date: String?
    var dateFormatted: Date?

    init(id: String? = nil, Weight: String, Body: String, date: String? = nil, dateFormatted: Date? = nil) {
            
        self.id = id
        self.Weight = Weight
        self.Body = Body
        self.date = date
        self.dateFormatted = dateFormatted

    }

 }
 
 @IBOutlet weak var logList: UITableView!
 @IBOutlet weak var logTitle: UILabel!
 var Diary = [Diary]()
 var Logs: [Log] = [Log].init()
 
 override func viewDidLoad() {
    super.viewDidLoad()
    self.fetchData(for: todayDate)
}

GETTING DATA

 func fetchData(for date: String) {

     guard let userId = Auth.auth().currentUser?.uid else { return }
     let LogRef = Database.database().reference().child("users/\(userId)/Log")
     LogRef.removeAllObservers()
     databaseRef = LogRef.child(date)
     databaseRef.observe(.value, with: {(snapshot) in
         self.Diary.removeAll()
         self.Logs.removeAll()
         if snapshot.childrenCount>0 {
             for title in snapshot.children.allObjects as! [DataSnapshot] {
                     print("title = ", title)
                 if let logObject = title.value as? [String: AnyObject],
                    let title = logObject["Body"] as? String,
                    let Weight = logObject["Weight"] as? String {
                     let title = Diary(id: title.key, Body: Body, Weight: Weight)
                     self.Diary.append(title)
                     if var Log = self.Logs.first(where: {$0.title == title}) {
                         Log.Diary.append(title)
                     }else {
                         self.Logs.append(Log.init(title: title, Diary: [title]))
                     }
                 }else if title.key == "logTitle",
                          let logTitle = title.value as? String {
                     self.logTitle.text = logTitle
                 }
             }
         }
         self.logList.reloadData()
     })
 }

TABLEVIEW CODE RELATED:

 func numberOfSections(in tableView: UITableView) -> Int {
     return self.Logs.count
 }

 func tableView(_ tableView: UITableView, titleForHeaderInSection section: Int) -> String? {
     return self.Logs[section].title.uppercased()
 }

 public func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
     if self.hiddenSections.contains(section) {
             return 0
         }
     return self.Logs[section].Diary.count
 }

 public func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
     let cell = logList.dequeueReusableCell(withIdentifier: "cell", for: indexPath) as! LogTableViewCell
     let title: Diary = self.Logs[indexPath.section].Diary[indexPath.row]
     cell.body.text = title.Body
     cell.weight.text = title.Weight
    
     return cell
 }

 }

CodePudding user response：

It largely comes down to this line:

if var Log = self.Logs.first(where: {$0.title == title}) {
    Log.Diary.append(title)
}

If a Log is a class instance, that changes the Diary array of a Log in the array self.Logs.

But if a Log is a struct instance, it doesn't. var Log is a copy, and changing it has no effect on anything in self.Logs.

For the workaround see my https://stackoverflow.com/a/56916573/341994. As I say there:

When you have an array of struct, then in order to make a change to a struct within the array, you must refer to that struct by index.

if let index = self.Logs.firstIndex(where: {$0.title == title}) {
    self.Logs[index].Diary.append(title)
}