几乎是Marc和Chris所说的虽然我更喜欢在应用程序退出时更改值，以防应用程序的多个区域需要了解它。
代码：

Pretty much what Marc and Chris said, though I prefer to change the value when the app quits in case there're multiple areas of the application that need to know about it. In code:

// -applicationDidFinishLaunching:
[[NSUserDefaults standardUserDefaults] registerDefaults:[NSDictionary dictionaryWithObjectsAndKeys:[NSNumber numberWithBool:YES],@"firstLaunch",nil]];
// to check it:
[[NSUserDefaults standardUserDefaults] boolForKey:@"firstLaunch"];
// -applicationWillTerminate:
[[NSUserDefaults standardUserDefaults] setBool:NO forKey:@"firstLaunch"];