背景音乐不再播放了

Question

我一直在使用此处iOS background music problems中所述的代码，我无法弄清楚如何在AppDelegate.h文件中声明出口的答案...我一直把它放在任何地方但它仍然没有...

这些是我的代码：

AppDelegate.h

#import <UIKit/UIKit.h>
#import <AVFoundation/AVAudioPlayer.h>
#import "ViewController.h"

@interface AppDelegate : UIResponder <UIApplicationDelegate> {

    AVAudioPlayer *audio2;
    IBOutlet UISlider *VolumeS2;
    AVAudioPlayer *audioPlayer2;
    NSTimer *VolumeTimer2;


}
@property (nonatomic, retain)AVAudioPlayer *audio2;


@property (strong, nonatomic) UIWindow *window;

@end

Appdelegate.m

#import "AppDelegate.h"

@implementation AppDelegate

@synthesize window = _window;

- (void)applicationDidEnterBackground:(UIApplication *)application {
    [[NSUserDefaults standardUserDefaults] setObject:nil forKey:@"music"]; }

ViewController.m

- (void)viewDidLoad
{
    if ([[NSUserDefaults standardUserDefaults] stringForKey:@"music"] == nil) {

            NSError *err;
    NSString *path2 = [[NSBundle mainBundle]
                       pathForResource:@"EasyLemon" ofType:@"mp3"];

    self.audio2 = [[AVAudioPlayer alloc] initWithContentsOfURL:[NSURL fileURLWithPath:path2] error:&err];
    audio2.delegate = self;
    audio2.numberOfLoops = -1;
    [audio2 play];


        [[NSUserDefaults standardUserDefaults] setObject:@"-" forKey:@"music"]; }



    animation.animationImages = [NSArray arrayWithObjects:
                                 [UIImage imageNamed:@"city.png"],
                                 [UIImage imageNamed:@"city2.png"],
                                 [UIImage imageNamed:@"city3.png"], nil];

    [animation setAnimationRepeatCount:0];
    animation.animationDuration = 1;
    [animation startAnimating];

}

- (void)applicationDidBecomeActive:(UIApplication *)application {
    NSError *err;
    NSString *path2 = [[NSBundle mainBundle]
                       pathForResource:@"EasyLemon" ofType:@"mp3"];

    self.audio2 = [[AVAudioPlayer alloc] initWithContentsOfURL:[NSURL fileURLWithPath:path2] error:&err];
    audio2.delegate = self;
    audio2.numberOfLoops = -1;
    [audio2 play];

    [[NSUserDefaults standardUserDefaults] setObject:@"-" forKey:@"music"]; }

很抱歉长代码......我只是想不通怎么做。