爲什麼回負值

Question

我想顯示的目錄及其持續時間內的音頻文件的列表，以便讓我使用時間：

AVAudioPlayer * sound = [[AVAudioPlayer alloc] initWithContentsOfURL:[NSURL fileURLWithPath:path] error:nil]; 

NSLog([NSString stringWithFormat:@"%f", sound.duration]); 

cell.detailTextLabel.text =[NSString stringWithFormat:@"Duration: %.2f sec", sound.duration]; 

但有時sound.duration返回負值。我想知道爲什麼，以及如何解決它。

問候

Answer 1

希望這將幫助你.. 在你的代碼，你在打印的NSLog沒有分配和錯誤的格式，以便它在零下給。所以檢查一次。

AVAudioPlayer * sound = [[AVAudioPlayer alloc] initWithContentsOfURL:[NSURL URLWithString:@"/Users/apple/Desktop/LabelTextDemo/LabelTextDemo/song2.caf"] error:nil]; 

NSLog(@"%@",[NSString stringWithFormat:@"%.2f", sound.duration]); 

Answer 2

AudioFileID      audioFile; 
CFDictionaryRef piDict = nil; 
UInt32 piDataSize = sizeof(piDict); 

if (noErr != AudioFileOpenURL((CFURLRef)[NSURL fileURLWithPath:filePath], 0x01, kAudioFileCAFType, &audioFile)) 
{ 
    return [NSDictionary dictionaryWithObjectsAndKeys:[NSString stringWithString:filePath], @"FilePath", @"Unknown",@"Title",@"Unknown",@"Album",@"Unknown",@"Artist",@"0", @"Duration", nil]; 
} 
if(noErr != AudioFileGetProperty(audioFile, kAudioFilePropertyInfoDictionary, &piDataSize, &piDict)) 
{ 
    AudioFileClose(audioFile); 
    return [NSDictionary dictionaryWithObjectsAndKeys:[NSString stringWithString:filePath], @"FilePath", @"Unknown",@"Title",@"Unknown",@"Album",@"Unknown",@"Artist",@"0", @"Duration", nil]; 
} 

AudioFileClose(audioFile); 

if(piDict) 
{ 
    NSString * duration = @"0"; 
    CFStringRef  durationString = nil; 
    if (piDict && CFDictionaryGetValueIfPresent(piDict, CFSTR(kAFInfoDictionary_ApproximateDurationInSeconds), (const void **) &durationString)) 
    { 
     duration = (NSString*)durationString; 
     duration = [duration stringByReplacingOccurrencesOfString:@"," withString:@""]; 
    } 
    if (duration) 
     [songInfomationDictionary setObject:duration forKey:@"Duration"]; 


    CFRelease(piDict); 
    //get duration as string 
} 
return nil;