我在 Storyboard 中的 UITableView 中放置了一个事件指示器。 我怎样才能将它居中放置在屏幕中间和表格 View 的前面？

我试过:

self.activityIndicator.center = self.tableView.center

但是现在，事件指示器位于 View 的中上部!

最佳答案

要在 UITableView 中加载数据时显示事件指示器，您可以创建一个 UIView 并将其添加到主视图(在 UITableView 的中心) .如果你想显示如下图:

您可以使用函数 setLoadingScreen 和 removeLoadingScreen 来做到这一点(如果您想查看示例项目，可以转到 here ):

class TableViewController: UITableViewController {

    // MARK: Properties

    /// Data source of the tableView
    var rows: [String] = []

    /// View which contains the loading text and the spinner
    let loadingView = UIView()

    /// Spinner shown during load the TableView
    let spinner = UIActivityIndicatorView()

    /// Text shown during load the TableView
    let loadingLabel = UILabel()


    // MARK: Methods

    override func viewDidLoad() {

        super.viewDidLoad()

        setLoadingScreen()

        loadData()

    }

    override func didReceiveMemoryWarning() {

        super.didReceiveMemoryWarning()

    }


    // MARK: - Table view data source

    override func numberOfSections(in tableView: UITableView) -> Int {

        return 1

    }

    override func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {

        return rows.count

    }

    override func tableView(tableView: UITableView, cellForRowAt indexPath: NSIndexPath) -> UITableViewCell {

        let cell = tableView.dequeueReusableCell(withIdentifier: "myCell", for: indexPath)!
        cell.textLabel!.text = rows[indexPath.row]

        return cell

    }


    // MARK: Private methods

    // Load data in the tableView
    private func loadData() {

        // Simulate a delay of some operations as a HTTP Request            
        DispatchQueue.main.asyncAfter(deadline: .now() + .milliseconds(20)) {

            self.rows = ["Row 1", "Row 2", "Row 3", "Row 4", "Row 5"]

            self.tableView.reloadData()
            self.tableView.separatorStyle = .singleLine
            self.removeLoadingScreen()

        }

    }

    // Set the activity indicator into the main view
    private func setLoadingScreen() {

        // Sets the view which contains the loading text and the spinner
        let width: CGFloat = 120
        let height: CGFloat = 30
        let x = (tableView.frame.width / 2) - (width / 2)
        let y = (tableView.frame.height / 2) - (height / 2) - (navigationController?.navigationBar.frame.height)!
        loadingView.frame = CGRect(x: x, y: y, width: width, height: height)

        // Sets loading text
        loadingLabel.textColor = .gray
        loadingLabel.textAlignment = .center
        loadingLabel.text = "Loading..."
        loadingLabel.frame = CGRect(x: 0, y: 0, width: 140, height: 30)

        // Sets spinner
        spinner.activityIndicatorViewStyle = .gray
        spinner.frame = CGRect(x: 0, y: 0, width: 30, height: 30)
        spinner.startAnimating()

        // Adds text and spinner to the view
        loadingView.addSubview(spinner)
        loadingView.addSubview(loadingLabel)

        tableView.addSubview(loadingView)

    }

    // Remove the activity indicator from the main view
    private func removeLoadingScreen() {

        // Hides and stops the text and the spinner
        spinner.stopAnimating()
        spinner.isHidden = true
        loadingLabel.isHidden = true

    }

}

关于swift - 将事件指示器放在 uitableview 上，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/29311093/