内容视图未显示在UITableViewCell上

Question

This is a part of my storyboard:

this is my running app:

This is my part of codes:

override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        if indexPath.section == 0 {
            if indexPath.row == 0 {
                 return super.tableView(tableView, cellForRowAt: indexPath)
            } else {
                tableView.register(SubTextFieldCell.self, forCellReuseIdentifier: "SubTextFieldCell")
                let cell = tableView.dequeueReusableCell(withIdentifier: "SubTextFieldCell", for: indexPath) as! SubTextFieldCell

//                cell.deleteButton.isEnabled = true
//                cell.subTextfield.text = "OK"

                print("indexPath.row: \(indexPath.row)")

                return cell
            }
...

I have already connected the button and the textfield in various places and I can guarantee that this part is not wrong, but when I click the Add button in the first row, I only get a cell without any content.

If I use code like this cell.deleteButton... , Xcode will report an error:

Thread 1: Fatal error: Unexpectedly found nil while unwrapping an Optional value

Then I tried to use the viewWithTag method to see if show the content, but I still get the same error as before.

This is the first time I have encountered this kind of error. I have no error with similar code and methods in my other programs.

Answer 1

When you configure custom cells inside a storyboard file, you don't need to call register(_:forCellReuseIdentifier:) because the storyboard should have done that for you.

The reason deleteButton is nil is because by re-registering the cell class as you did, you overwrote what the storyboard registered for you. All cells created by dequeueing with that reuse identifier will have no connection to the storyboard and simply be empty.

Assuming all the @IBOutlet s and reuse identifiers and things are set up (which you said you did), then simply dequeue the cell with the reuse identifier set up in storyboard.

Dequeue Cell Example:

override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
    if indexPath.section == 0 {
        if indexPath.row == 0 {
            return super.tableView(tableView, cellForRowAt: indexPath)
        } else {
            // Registering again is unnecessary, because the storyboard should have already done that.
//            tableView.register(SubTextFieldCell.self, forCellReuseIdentifier: "SubTextFieldCell")
            let cell = tableView.dequeueReusableCell(withIdentifier: "SubTextFieldCell") as! SubTextFieldCell

            cell.deleteButton.isEnabled = true
            cell.subTextfield.text = "OK"

            return cell
        }
    } else {
        ...
    }
}

Note:

Even in cases where you do need to register a class with a table view, you should only have to do this once. (For example, during viewDidLoad )

Even in those times, you should not call it every time you dequeue a cell. You're just making your app work harder.

Connecting views to cells in Storyboard

Set a subclass to the table view

Set a subclass to the first prototype cell

Set a reuse identifier to the prototype cell

Make sure subview ( UIButton , etc.) is connected to property with @IBOutlet (subclass code shown below)

Example UITableViewController subclass:

class MyTableViewController: UITableViewController {

    override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return 2
    }

    override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        if indexPath.row == 0 {
            let cell = tableView.dequeueReusableCell(withIdentifier: "MyFirstCell", for: indexPath) as! MyFirstTableViewCell

            // Configure cell if needed
            cell.myButton.setTitle("New Button Text", for: .normal)
            cell.myButton.tintColor = .green

            return cell
        } else {
            let cell = tableView.dequeueReusableCell(withIdentifier: "MySecondCell", for: indexPath) as! MySecondTableViewCell

            // Configure cell if needed
            cell.myTextField.backgroundColor = .red

            return cell
        }
    }

}

Example UITableViewCell subclass:

class MyFirstTableViewCell: UITableViewCell {

    @IBOutlet weak var myButton: UIButton!

}

Result: