傳遞參數與AudioServicesAddSystemSoundCompletion

Question

我試圖通過UILabel與AudioServicesAddSystemSoundCompletion但我無法操縱completionCallback方法內的值。我使用ARC和Xcode建議添加(_bridge void*)。

任何幫助將不勝感激。

-(void) playWordSound:(UILabel *)label 
{ 
    NSString *path; 
    SystemSoundID soundId; 
    switch (label.tag) 
    { 
     case 1: 
      .......... 
      break; 
    } 
    NSURL *url = [NSURL fileURLWithPath:path]; 
    AudioServicesCreateSystemSoundID((CFURLRef)objc_unretainedPointer(url), &soundId); 
    AudioServicesPlaySystemSound(soundId); 
    AudioServicesAddSystemSoundCompletion (soundId, NULL, NULL, 
              completionCallback, 
              (__bridge void*) label); 
} 


static void completionCallback (SystemSoundID mySSID, void* data) { 
    NSLog(@"completion Callback"); 
    AudioServicesRemoveSystemSoundCompletion (mySSID); 
    //the below line is not working 
    //label.textColor = [UIColor colorWithRed:0 green:0 blue:0 alpha:1]; 
} 

Answer 1

在完成處理程序中，標籤存儲在data中。你需要__bridge它回來使用它。

static void completionCallback (SystemSoundID mySSID, void* data) { 
    NSLog(@"completion Callback"); 
    AudioServicesRemoveSystemSoundCompletion (mySSID); 
    UILabel *label = (__bridge UILabel*)data; 
    label.textColor = [UIColor colorWithRed:0 green:0 blue:0 alpha:1]; 
}