Thanks a lot, Jordan. > 在 2017年12月15日，上午2:08，Jordan Rose <jordan_r...@apple.com> 写道： > > > >> On Dec 13, 2017, at 23:05, 吴君恺 via swift-users <swift-users@swift.org >> <mailto:swift-users@swift.org>> wrote: >> >> Hello community, >> >> I just encountered a pretty weird behavior when I subclass >> `UINavigationController` without overriding any initializers. >> >> Simple Code: >> >> import UIKit >> >> class MyViewController: UINavigationController { >> >> let value: Int = { >> print("member init") >> return 3 >> }() >> } >> >> let _ = MyViewController(rootViewController: UIViewController()) >> >> output is: >> >> member init >> member init >> >> In fact any member variables declared in this subclass is initialized twice >> but deinitialized only once. >> This phenomenon only appears when using `init(rootViewController:)`. >> >> CMIW, It looks like Swift somehow treat this initializer as a designated >> initializer, rather than a convenience one. >> >> Any Ideas? > > Your analysis is correct. The problem is that UINavigationController's header > file doesn't properly declare which initializers are designated and which are > convenience. Fortunately, you're not the first to notice this; it's tracked > by the UIKit folks as rdar://problem/27255526 <rdar://problem/27255526>. I'll > poke them about it. > > Thanks for bringing it up! > Jordan >
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