Objective-C将变量设置为从方法返回的内容

Question

我有这段代码：

-(NSURL *)urlOfCurrentlyPlayingInPlayer:(AVPlayer *)player{
// get current asset
AVAsset *currentPlayerAsset = player.currentItem.asset;

// make sure the current asset is an AVURLAsset
if (![currentPlayerAsset isKindOfClass:AVURLAsset.class]) return nil;

// return the NSURL
return [(AVURLAsset *)currentPlayerAsset URL];

}

为什么我不能这样做？

NSURL *currentSong=[urlOfCurrentlyPlayingInPlayer:_audioPlayer1];

错误消息是“预期表达式”，NSURL的N用红色下划线标出

抱歉noob问题

Answer 1

假设urlOfCurrentlyPlayingInPlayer在同一个类中声明：

NSURL *currentSong = [self urlOfCurrentlyPlayingInPlayer:_audioPlayer1];

如果它是某个其他类的实例方法，那么它将是

NSURL *currentSong = [myInstanceOfSomeOtherClass urlOfCurrentlyPlayingInPlayer:_audioPlayer1];