1.为什么要实现以下初始化方法?
@interface TRMusicListController ()
@property(strong, nonatomic)TRMusicPlayingController *playingVC;
@end
@implementation TRMusicListController
- (TRMusicPlayingController *)playingVC { // if (!_playingVC) { _playingVC = [[TRMusicPlayingController alloc]initWithNibName:@"TRMusicPlayingController" bundle:nil]; } return _playingVC; }
- init初始化 和initWithNibName:@"TRMusicPlayingController" bundle:nil]的区别?