Xcode Playground使用简单的UITableViewController代码崩溃

Question

I encountered a very strange problem with a UITableViewController subclass instance in the Xcode Playground. I registered two UITableViewCell s programmatically in viewDidLoad , and dequeued cells in cellForRowAt method:

import UIKit
import PlaygroundSupport

class ViewController: UITableViewController {
  override func viewDidLoad() {
    super.viewDidLoad()
    tableView.register(UITableViewCell.self, forCellReuseIdentifier: "cell1")
    tableView.register(UITableViewCell.self, forCellReuseIdentifier: "cell2")
  }

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

  override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
    switch indexPath.row {
    case 0:
      return tableView.dequeueReusableCell(withIdentifier: "cell1", for: indexPath)
    case 1:
      return tableView.dequeueReusableCell(withIdentifier: "cell2", for: indexPath)
    default:
      fatalError()
    }
  }
}

let vc = ViewController(style: .plain)
PlaygroundPage.current.liveView = vc

But the Playground throws an NSException and shows:

error: Execution was interrupted, reason: signal SIGABRT.
The process has been left at the point where it was interrupted, use "thread return -x" to return to the state before expression evaluation.

Note that this code works well in a legit Xcode Project with an iPhone simulator. Am I making a mistake here, or is it a bug?

I'm using Version 10.3 (10G8).

Answer 1

Curious bug...

This works fine:

class ViewController: UITableViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        tableView.register(UITableViewCell.self, forCellReuseIdentifier: "cell1")
        tableView.register(UITableViewCell.self, forCellReuseIdentifier: "cell2")
    }

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

    override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        return tableView.dequeueReusableCell(withIdentifier: "cell1", for: indexPath)
    }
}

But this crashes:

class ViewController: UITableViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        tableView.register(UITableViewCell.self, forCellReuseIdentifier: "cell1")
        tableView.register(UITableViewCell.self, forCellReuseIdentifier: "cell2")
    }

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

    override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        return tableView.dequeueReusableCell(withIdentifier: "cell2", for: indexPath)
    }
}

The only difference is that the example that crashes is returning the second registered cell.

If you swap the order of the .register() statements, then "cell2" works and "cell1" crashes.

---

EDIT (Edit 2: we need to assign .delegate and .dataSource -- could be done in loadView() or viewDidLoad() )

Note that, since registering (and using) only one cell works as-is, it shouldn't be necessary to set the view. However, if you do set the view in loadView() the code will run in Playground without crashing:

class ViewController: UITableViewController {

    override func loadView() {
        let v = UITableView()
        v.delegate = self
        v.dataSource = self
        self.view = v
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        tableView.register(UITableViewCell.self, forCellReuseIdentifier: "cell1")
        tableView.register(UITableViewCell.self, forCellReuseIdentifier: "cell2")
    }

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

    override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        switch indexPath.row {
        case 0:
            return tableView.dequeueReusableCell(withIdentifier: "cell1", for: indexPath)
        case 1:
            return tableView.dequeueReusableCell(withIdentifier: "cell2", for: indexPath)
        default:
            fatalError()
        }
    }
}