如何在另一种方法之前强制执行一种方法？

我有2种方法。 一种方法开始播放音频文件（.mp3），另一种方法更新UIToolBar以显示一个按钮（PLAY或PAUSE）。这两种方法在下面称为顺序：如何在另一种方法之前强制执行一种方法？

//Adds some UIBarButtonItems to a UIToolBar 
[self togglePlayer]; 
//Uses AVAudioPlayer 
[audioPlayer play];

TogglePlayer执行此：

-(void)togglePlayer 
{ 

    NSLog(@"Toggling Player"); 

    NSArray *barButtonItems; 
    UIBarButtonItem *barButtonSpaceL; 
    UIBarButtonItem *barButtonSpaceR; 
    UIBarButtonItem *barButtonItemPlayer; 
    UIBarButtonItem *barButtonItemCancel; 
    UIBarButtonItem *barButtonItemLyrics; 
    UIBarButtonItem *barButtonItemTweet; 

    if([myToolbar.items count] > 0){ 

     NSEnumerator *enumerator = [myToolbar.items objectEnumerator]; 
     id object; 
     while ((object = [enumerator nextObject])) { 

      [object release]; 
      object = nil; 
     } 
    } 

    if(!downloadInProgress){ 

    barButtonSpaceL = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemFlexibleSpace target:self action:nil]; 
    barButtonSpaceR = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemFlexibleSpace target:self action:nil]; 

    if(thePlayerState == PLAYER_PLAYING){ 
    barButtonItemPlayer = [[UIBarButtonItem alloc] initWithImage:[UIImage imageNamed:@"pauseIcon.png"] style:UIBarButtonItemStylePlain target:self action:@selector(pauseButtonPressed:)]; 
    barButtonItemLyrics = [[UIBarButtonItem alloc] initWithTitle:@"Lyrics" style:UIBarButtonItemStyleBordered target:self action:@selector(switchPageLyrics:)]; 
    barButtonItemTweet = [[UIBarButtonItem alloc] initWithTitle:@"Tweet This" style:UIBarButtonItemStyleBordered target:self action:@selector(tweetSong:)]; 

     if(canTweet){ 
     barButtonItems = [NSArray arrayWithObjects:barButtonItemTweet, barButtonSpaceR, barButtonItemPlayer, barButtonSpaceL, barButtonItemLyrics, nil]; 
     }else{ 
     barButtonItems = [NSArray arrayWithObjects:barButtonItemPlayer, barButtonSpaceR, barButtonItemLyrics, nil];   
     } 

    }else if(thePlayerState == PLAYER_PAUSED){ 

    barButtonItemPlayer = [[UIBarButtonItem alloc] initWithImage:[UIImage imageNamed:@"playIcon.png"] style:UIBarButtonItemStylePlain target:self action:@selector(playButtonPressed:)]; 
    barButtonItemLyrics = [[UIBarButtonItem alloc] initWithTitle:@"Lyrics" style:UIBarButtonItemStyleBordered target:self action:@selector(switchPageLyrics:)]; 
    barButtonItemTweet = [[UIBarButtonItem alloc] initWithTitle:@"Tweet This" style:UIBarButtonItemStyleBordered target:self action:@selector(tweetSong:)]; 


     if(canTweet){ 
      barButtonItems = [NSArray arrayWithObjects:barButtonItemTweet, barButtonSpaceR, barButtonItemPlayer, barButtonSpaceL, barButtonItemLyrics, nil]; 
     }else{ 
      barButtonItems = [NSArray arrayWithObjects:barButtonItemPlayer, barButtonSpaceR, barButtonItemLyrics, nil];   
     } 

    }else{ 

    //PLAYER OFF  
    barButtonItems = [NSArray arrayWithObjects:barButtonSpaceL, nil]; 

    } 
     [myToolbar setItems:barButtonItems];  

    }else{ 


     barButtonSpaceL = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemFlexibleSpace target:self action:nil]; 
     barButtonSpaceR = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemFlexibleSpace target:self action:nil]; 
     barButtonItemCancel = [[UIBarButtonItem alloc] initWithTitle:NSLocalizedString(@"VC1_DownloadCancel", @"") style:UIBarButtonItemStyleBordered target:self action:@selector(downloadCancelled:)];   

     if(thePlayerState == PLAYER_PLAYING){ 
      barButtonItemPlayer = [[UIBarButtonItem alloc] initWithImage:[UIImage imageNamed:@"pauseIcon.png"] style:UIBarButtonItemStylePlain target:self action:@selector(pauseButtonPressed:)]; 
      barButtonItems = [NSArray arrayWithObjects:barButtonItemPlayer, barButtonSpaceR, barButtonItemCancel, nil]; 

     }else if(thePlayerState == PLAYER_PAUSED){ 
      barButtonItemPlayer = [[UIBarButtonItem alloc] initWithImage:[UIImage imageNamed:@"playIcon.png"] style:UIBarButtonItemStylePlain target:self action:@selector(playButtonPressed:)]; 
      barButtonItems = [NSArray arrayWithObjects:barButtonItemPlayer, barButtonSpaceR, barButtonItemCancel, nil]; 

     }else{ 

     //PLAYER OFF 
      barButtonItems = [NSArray arrayWithObjects:barButtonSpaceL, barButtonItemCancel, barButtonSpaceR, nil]; 
     } 

     [myToolbar setItems:barButtonItems]; 


    } 

}

我打电话以上述顺序的方法中，以使（暂停）键将在时刻显示的歌曲开始播放。但是，问题在于歌曲首先播放，并且UIToolBar保持不变（从2秒到5秒）直到按钮被添加并显示。

我想要的是在歌曲开始播放的同时（即无延迟）显示按钮。有没有办法做到这一点？

来源

2010-03-27 RexOnRoids

神圣的内存泄漏，蝙蝠侠！你已经'分配'了一大堆按钮，但从来没有'释放'它们。 – 2010-03-27 13:57:13

为了更新gui，您需要给它一个实际更新gui的机会。由于音频播放发生在另一个线程中，因此它将立即开始播放。但是，由于您可能在gui中发生了事件（如触摸事件），并且您没有从该函数返回，所以负责更新gui的代码尚未运行。

有关Cocoa框架

信息，请参阅http://developer.apple.com/iphone/library/documentation/iPhone/Conceptual/iPhoneOSProgrammingGuide/ApplicationEnvironment/ApplicationEnvironment.html#//apple_ref/doc/uid/TP40007072-CH7-SW2使用此函数来调用播放应该工作，你想要的方式。这会在您处理当前事件后将该事件放置到呼叫中。

- (void)performSelector:(SEL)aSelector withObject:(id)anArgument afterDelay:(NSTimeInterval)delay

你举的例子：

//Adds some UIBarButtonItems to a UIToolBar 
[self togglePlayer]; 
//Uses AVAudioPlayer 
[audioPlayer performSelector:@SEL(play) withObject:nil afterDelay:0];

来源

2010-03-27 13:37:12 Eld

另一种方法可能是准备系统来播放音频文件，使用

[audioPlayer prepareToPlay];

某处你的初始化代码，例如在viewDidLoad。这样一旦你想要播放音频，一切都将被设置，并且play方法不会造成显着的延迟。（不是在你的用户界面代码，而不是实际的播放）

来源

2010-11-18 01:57:30 mvds

如何在另一种方法之前强制执行一种方法？

回答

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