在Appdelegate.h 
 
我在Appdelegate.h和Appdelegate.m文件中导入了playerviewcontroller.
我在Appdelegate.h和Appdelegate.m文件中导入了playerviewcontroller.
@class PlayerViewController; @property(nonatomic)float volumeDelegate;
在Appdelegate.m
@synthesize volumeDelegate;
 - (void)volumeChanged:(NSNotification *)notification
 {
volumeDelegate =1.0
    PlayerViewController *volumeObject=[[PlayerViewController alloc]init];
[volumeObject setVolumeForAVAudioPlayer];
} 
 在Playerviewcontroller.h
-(void)setVolumeForAVAudioPlayer;
在Playerviewcontroller.m
@interface PlayerViewController ()
{
AppDelegate *appdelegate;
 }
  -(void)viewDidLoad
  {
  appdelegate = (AppDelegate*)[[UIApplication sharedApplication] delegate];
  }
  -(void)setVolumeForAVAudioPlayer
  {
[appdelegate.sharedplayer  setVolume:appdelegate.volumeDelegate];
NSLog(@"System Volume in player view:  %f",appdelegate.volumeDelegate);
 } 
 当我运行这个我得到volumeDelegate值为零如下.
播放器视图中的系统音量:0.000000000
我在这里做的错误是什么
解决方法
 在访问该值之前,您是否在下面写下一行,
        appdelegate = (AppDelegate *)[UIApplication sharedApplication].delegate;
那么这个电话应该是打电话,
-(void)setVolumeForAVAudioPlayer
{
    [appdelegate.sharedplayer  setVolume:appdelegate.volumeDelegate];
    NSLog(@"System Volume in player view:  %f",appdelegate.volumeDelegate);
}