cannot find protocol declaration for "RefreshAudioListViewDelegate"
1.PlayerListViewController.h文件时，首先发现#import "PlayerController.h",编译器会跑到PlayerController.h中。
2.在PlayerController.h中首先发现#import "PlayerListViewController.h"，编译器又会到PlayerListViewController中加载内容。
@interface PlayerListViewController : UIViewController< RefreshAudioListViewDelegate>这一句的时候，由于在PlayerController中定义代理的语句还没有加载，所以编译器会报错：
cannot find protocol declaration for "RefreshAudioListViewDelegate"
#import "PlayerListViewController.h"
