presentViewController:animated:completion: bug

2017-09-23 Update: the bug still persists in iOS 11.0 (15A372) 2019-05-26 Update: the bug still persists in iOS 12.2 (16E227)

Demonstration project of a bug in UIViewController presentViewController:animated:completion: on iOS 8.3.

Usage:

• Start the app on a device with iOS ~8.3~ 11.0 (iOS 8.1 also works, haven't tried w/ older versions)
• Wait until the app stops producing kCFRunLoop ... log lines (i.e. the main runloop goes to sleep):

   ... more lines
   2015-06-11 18:24:51.214 UIActivityViewControllerTest[526:45580] kCFRunLoopBeforeSources
   2015-06-11 18:24:51.214 UIActivityViewControllerTest[526:45580] kCFRunLoopBeforeWaiting
   2015-06-11 18:25:00.001 UIActivityViewControllerTest[526:45580] kCFRunLoopAfterWaiting
   2015-06-11 18:25:00.008 UIActivityViewControllerTest[526:45580] kCFRunLoopBeforeTimers
   2015-06-11 18:25:00.009 UIActivityViewControllerTest[526:45580] kCFRunLoopBeforeSources
   2015-06-11 18:25:00.010 UIActivityViewControllerTest[526:45580] kCFRunLoopBeforeWaiting

The last line should be kCFRunLoopBeforeWaiting

• Tap on the first row; this calls presentViewController:animated:completion to present a completely blank view controller w/ red background
• Notice how the red view controller failed to appear
• Tap anywhere on the screen, or shake the device, or wait until the clock on the status bar updates: the view controller should appear now
• Tap anywhere on the red view controller to dismiss it
• Tap on the second row; this calls presentViewController:animated:completion: and then calls CFRunLoopWakeUp(CFRunLoopGetCurrent())
• Notice how this time, no matter what the main runloop's state was, the view controller was presented correctly.

Rdar: http://openradar.appspot.com/19563577

Other people encountering the same issue:

• http://stackoverflow.com/questions/21075540/presentviewcontrolleranimatedyes-view-will-not-appear-until-user-taps-again/
• http://stackoverflow.com/questions/20320591/uitableview-and-presentviewcontroller-takes-2-clicks-to-display
• https://devforums.apple.com/thread/201431