I use the same book, had the same problem, but I decided how to fix it.
- Create a new xib file with
right-click the Quiz folder → New File → iOS → User Interface → Window → click Next
- click the Window.xib file, then find the object and drag it under the objects → select the third tab on the right → change this class to AppDelegate
click File Owner -> change this class to UIApplication -> click the 6th tab and connect the delegate to the window
- go to AppDelegate.h and place an IBOutlet in front of the UIWindow * window;
go to Window.xib and connect to the Outlets to Window.
Also in the plist file add the line key - the base name of the main file nib type - string value - mainwindow
Hope this helps.
Seungun ham
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