自定义方法

- (id)transformedValue:(id)value

{

   double convertedValue = [value doubleValue];

   int multiplyFactor = 0;

   NSArray *tokens = [NSArray arrayWithObjects:@"bytes",@"KB",@"MB",@"GB",@"TB",@“PB”, @“EB”, @“ZB”, @“YB”,nil];

   while (convertedValue > 1024) {

       convertedValue /= 1024;

       multiplyFactor++;

   }

   return [NSString stringWithFormat:@"%4.2f %@",convertedValue, [tokens objectAtIndex:multiplyFactor]];

}

系统自带方法

[NSByteCountFormatter stringFromByteCount:1999 countStyle:NSByteCountFormatterCountStyleFile];