无法从父级ViewController在UITableViewCell中设置变量

Question

I have a UITableView and a custom TableViewCell class, I am setting a non-null value in viewDidLoad method, but while setting the value to UITableViewCell in cellForRow method , the value magically becomes nil. I am unable to access the set variable from my custom UITableViewCell Here is the snippet of code. Print statement in ViewDidLoad prints the value while the one in cellForRowAtIndexPath returns nil

override func viewDidLoad() {
    super.viewDidLoad()
    Docco360Util.shared().getDoctorsWithResultBlock { (doctorObjects, error) in
        if let err = error{
            print(err)
        }else{
            self.doctors=doctorObjects
            print(doctorObjects![1].professionalHeader)//output is printed here
            self.doctorTableView.reloadData()
        }
    }

    // Do any additional setup after loading the view.
}

func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
    let identifierForUsers = "DoctorTableViewCell"
    var cell = tableView.dequeueReusableCell(withIdentifier: identifierForUsers, for: indexPath) as! DoctorTableViewCell
    if cell == nil{
        cell=DoctorTableViewCell(style: .default, reuseIdentifier: identifierForUsers)
    }
    print(self.doctors[indexPath.row].professionalHeader)//output in nil here
    cell.doctor=self.doctors[indexPath.row]
    return cell
}

Answer 1

func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {

    let cell = tableView.dequeueReusableCell(withIdentifier: "DoctorTableViewCell", for: indexPath) as! DoctorTableViewCell

    print(self.doctors[indexPath.row].professionalHeader)
    cell.doctor = self.doctors[indexPath.row]
    return cell
}

Answer 2

First, you should ensure that the closure of Docco360Util.shared().getDoctorsWithResultBlock is executed in the main (UI) thread. If not, you should put it into a DispatchQueue.main.async block.

Then, you should verify that the result block is executed (eg the print statement prints something). Btw, why do you call print(doctorObjects![1].professionalHeader) with index 1 and not 0 ? In tableView(tableView:cellForRowAt:) you element with index 0 - maybe this doctor is nil ?

You could start by setting a breakpoint to your property declaration, a watchpoint, or implement a property observer ( willSet ) and add a breakpoint her, to check if somebody is messing up with your variables.

If all this does not help, you might want to post more code, expecially all lines of code where you write your self.doctors array.

Answer 3

I could finally fix it. The problem was in declaration of variables. I was using Objective-C header file for declarations. While declaring I declared them as "weak" instead of "retain" and that was causing the problem.