RespondsToSelector 返回假阴性?
我目前正在使用 -respondsToSelector:
,如下所示:
if (![moviePlayer respondsToSelector:@selector(currentPlaybackTime)]) {
NSLog(@"Cannot get current playbackTime on %@", moviePlayer);
return;
}
其中 moviePlayer 是实例化的 MPMoviePlayerController 对象。我做了很多其他类似的选择器检查,所以我知道几乎所有其他东西都工作正常,但由于某种原因,此respondsToSelector 检查返回 false,即使我做了类似 time = [moviePlayer currentPlaybackTime]< /代码>,它工作正常。这是在 4.0+ iOS 上,所以没有理由返回 false。
有什么原因会发生这种情况吗?
I'm currently using -respondsToSelector:
like so:
if (![moviePlayer respondsToSelector:@selector(currentPlaybackTime)]) {
NSLog(@"Cannot get current playbackTime on %@", moviePlayer);
return;
}
where moviePlayer is an instantiated MPMoviePlayerController object. I do a lot of other similar selector checks, so I know that pretty much everything else is working fine, but for some reason, this respondsToSelector check returns false, even though if I do something like time = [moviePlayer currentPlaybackTime]
, it works fine. This is on 4.0+ iOS, so there's no reason for it to return false.
Any reasons why this would happen?
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根据 iOS 类参考,currentPlaybackTime
是MPMusicPlayerController
的属性,而不是MPMoviePlayerController
。MPMusicPlayerController:
http://developer.apple.com/库/ios/#documentation/MediaPlayer/Reference/MPMusicPlayerController_ClassReference/Reference/Reference.html
MPMoviePlayerController:
http://developer.apple.com/ library/ios/#documentation/MediaPlayer/Reference/MPMoviePlayerController_Class/MPMoviePlayerController/MPMoviePlayerController.html
它可能是没有访问器的MPMoviePlayerController
的私有属性。编辑(参见评论)
确定操作系统版本:
According to the iOS class reference,currentPlaybackTime
is a property ofMPMusicPlayerController
, notMPMoviePlayerController
.MPMusicPlayerController:
http://developer.apple.com/library/ios/#documentation/MediaPlayer/Reference/MPMusicPlayerController_ClassReference/Reference/Reference.html
MPMoviePlayerController:
http://developer.apple.com/library/ios/#documentation/MediaPlayer/Reference/MPMoviePlayerController_Class/MPMoviePlayerController/MPMoviePlayerController.html
It may be a private property ofMPMoviePlayerController
that does not have an accessor.EDIT (see comments)
Determine OS version: