AppKit: showing the “open” panel on startup in a document-based application

Up: AppKit

Disclaimer: I am an AppKit newbie. Take all of this with a grain of salt.

In an AppKit document-based application, it can be helpful to show the “open” panel on startup, with the option of creating a new document from that open panel.

To do so, first override applicationShouldOpenUntitledFile() in NSApplicationDelegate to return false (otherwise it’ll open an untitled file on startup):

func applicationShouldOpenUntitledFile(
  _ app: NSApplication
) -> Bool {
  return false
}

To show the open panel, override applicationShouldHandleReopen() to trigger the openDocument action (passing in nil as the irrelevant sender) if there are no open windows (including panels like the open panel):

func applicationShouldHandleReopen(
  _ app: NSApplication,
  hasVisibleWindows: Bool
) -> Bool {
  if app.windows.count(where: { $0.isVisible }) > 0 {
    return true
  }

  NSDocumentController.shared.openDocument(nil)
  return false
}

Do not override applicationDidFinishLaunching() to show the open panel, or you’ll get two open panels.