In my app I have a background task performed on a custom DispatchQueue. When it has completed, I update the UI in DispatchQueue.main.async. In a particular case, the app then needs to show a modal window that contains a table view, but I have noticed that when scrolling through the tableview, it only responds very slowly.
It appears that this happens when the table view in the modal window is presented in DispatchQueue.main.async. Presenting it in perform(_:with:afterDelay:) or in a Timer.scheduledTimer(withTimeInterval:repeats:block:) on the other hand works. Why? This seems like an ugly workaround.
I created FB7448414 in November 2019 but got no response.
@NSApplicationMain
class AppDelegate: NSObject, NSApplicationDelegate {
func applicationDidFinishLaunching(_ aNotification: Notification) {
let windowController = NSWindowController(window: NSWindow(contentViewController: ViewController()))
// 1. works
// runModal(for: windowController)
// 2. works
// perform(#selector(runModal), with: windowController, afterDelay: 0)
// 3. works
// Timer.scheduledTimer(withTimeInterval: 0, repeats: false) { [self] _ in
// self.runModal(for: windowController)
// }
// 4. doesn't work
DispatchQueue.main.async {
self.runModal(for: windowController)
}
}
@objc func runModal(for windowController: NSWindowController) {
NSApp.runModal(for: windowController.window!)
}
}
class ViewController: NSViewController, NSTableViewDataSource, NSTableViewDelegate {
override func loadView() {
let tableView = NSTableView()
tableView.dataSource = self
tableView.delegate = self
tableView.addTableColumn(NSTableColumn())
let scrollView = NSScrollView(frame: CGRect(x: 0, y: 0, width: 400, height: 400))
scrollView.documentView = tableView
scrollView.hasVerticalScroller = true
scrollView.translatesAutoresizingMaskIntoConstraints = false
view = scrollView
}
func numberOfRows(in tableView: NSTableView) -> Int {
return 100
}
func tableView(_ tableView: NSTableView, viewFor tableColumn: NSTableColumn?, row: Int) -> NSView? {
let view = NSTableCellView()
let textField = NSTextField(labelWithString: "\(row)")
textField.translatesAutoresizingMaskIntoConstraints = false
view.addSubview(textField)
NSLayoutConstraint.activate([textField.leadingAnchor.constraint(equalTo: view.leadingAnchor), textField.trailingAnchor.constraint(equalTo: view.trailingAnchor), textField.topAnchor.constraint(equalTo: view.topAnchor), textField.bottomAnchor.constraint(equalTo: view.bottomAnchor)])
return view
}
}
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