How to reload tableview using view controller (swift)

Question

i'm quite new to this. I've spent some hours to go through the various questions on this topic but couldn't find an answer that fits to me question.

I have an viewcontroller (not a tableviewcontroller) with a tableview as subview. My question is how to reload the table data inside the :viewwillappear method of the view controller. Inside the method i can't "access" the tableview instance. (Also i understand i can't use reloaddata() because im not using a tableviewcontroller).

Do you know any simple solution? (i very much assume that a protocol could help here?)

this is the code in short:

class ViewController3: UIViewController, UITableViewDataSource, UITableViewDelegate {

    var Person_data = [Person]()

    override func viewDidLoad() {
        super.viewDidLoad()

        let tb: UITableView = UITableView(frame: CGRect(x: 10, y: 50, width: 200, height:600), style: UITableViewStyle.Plain)

        tb.dataSource = self
        tb.delegate = self
        super.view.addSubview(tb)

        fetch_data()
    }


        func tableView(tableview: UITableView, numberOfRowsInSection section: Int) -> Int {
            let rows = Person_data.count
            return rows
        }


       func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell
        {  
            let cell: UITableViewCell = UITableViewCell()
            cell.textLabel?.text = Person_data[indexPath.row].name
            return cell
        }

    override func viewWillAppear(animated: Bool) {
        super.viewWillAppear(animated)
        fetch_data()      
      // reload at this point

    } 


    func fetch_data() {

       let tb_fetchRequest = NSFetchRequest(entityName: "Person")
        do {

            let tb_fetchResults = try my_moc.executeFetchRequest(tb_fetchRequest) as? [Person]
            Person_data = tb_fetchResults!
        } catch let error as NSError {
                print("request error: \(error)")
            }

        }
    }

Solution 1

Your problem is that tb is a local variable, so it is not visible outside of viewDidLoad().

If you make tb a property (a.k.a. instance variable) of your view controller, then you can use it from any of the controller’s methods:

class ViewController3: UIViewController, UITableViewDataSource, UITableViewDelegate {

    var Person_data = [Person]()

    private var tb: UITableView?  // Now the scope of tb is all of ViewController3...

    override func viewDidLoad() {
        super.viewDidLoad()

        // ...so it is visible here...

        tb = UITableView(frame: CGRect(x: 10, y: 50, width: 200, height:600), style: UITableViewStyle.Plain)

        ...
    }

    override func viewWillAppear(animated: Bool) {
        super.viewWillAppear(animated)
        fetch_data()      

        tb?.reloadData()   // ...and it is also visible here.
    } 

Note that in your code, the fact that tb is a local variable doesn’t mean that your UITableView object disappears when viewDidLoad() finishes. It means that your reference to the UITableView disappears. The table view object itself lives on because it is added to your view hierarchy, but you don’t have a reference to it anymore because your variable went out of scope.

For further reading on the distinction between variables and the objects they reference, search for “scope” and “pass by reference.”

Solution 2

You can access your tableView IBOutlet in viewWillAppear:, you can also call reloadData. I'm not sure why you think you can't, but it should work fine.

Solution 3

You have to create a variable with link to tableView and create it before viewWillAppear.

class ViewController3: UIViewController, UITableViewDataSource, UITableViewDelegate {
    private let tableView = UITableView(frame: CGRect(x: 10, y: 50, width: 200, height:600), style: UITableViewStyle.Plain)
    var Person_data = [Person]()

    override func viewDidLoad() {
        super.viewDidLoad()

        tableView.dataSource = self
        tableView.delegate = self
        super.view.addSubview(tb)

        fetch_data()
    }

    override func viewWillAppear(animated: Bool) {
        super.viewWillAppear(animated)
        fetch_data()      
        tableView.reloadData()
    } 
}

Comments

[Netzer]

Thanks for the hint. I Took a deeper look at instance variables

[Paul Cantrell]

Also take a look at @Arsen’s answer, which shows how you can prevent tableView from being an optional be initializing it immediately. That technique often does not work with UI elements, but it does work in this case.

[Sylar]

Thank you from Swift 4 in 2019! 🎉