iOS 监听本地文件复制进度

做文件共享的时候，iTunes往app导入本地视频，实时监听文件的复制进度

 NSInteger lastSize = 0;         
 NSDictionary *fileAttrs = [[NSFileManager defaultManager] attributesOfItemAtPath:videoPath error:nil];                  
 NSInteger fileSize = [[fileAttrs objectForKey:NSFileSize] intValue];                       

do {                          
      lastSize = fileSize;                         
      [NSThread sleepForTimeInterval:0.5];                       
      self.isFinishedCopy = NO;                           
      fileAttrs = [[NSFileManager defaultManager] attributesOfItemAtPath:videoPath error:nil];                          
      fileSize = [[fileAttrs objectForKey:NSFileSize] intValue];                        
      NSLog(@"文件正在复制");                       
 } while (lastSize != fileSize);                      
 
 self.isFinishedCopy = YES;                      
 NSLog(@"%@文件复制完成");