判断时间格式时12小时制还是24小时制

+(BOOL)timeIs24HourFormat {    NSDateFormatter *formatter = [[NSDateFormatter alloc] init];    [formatter setDateStyle:NSDateFormatterNoStyle];    [formatter setTimeStyle:NSDateFormatterShortStyle];    NSString *dateString = [formatter stringFromDate:[NSDate date]];    NSRange amRange = [dateString rangeOfString:[formatter AMSymbol]];    NSRange pmRange = [dateString rangeOfString:[formatter PMSymbol]];    BOOL is24Hour = amRange.location == NSNotFound && pmRange.location == NSNotFound;    [formatter release];    return is24Hour;}