较简单的date转化成格式化的timeString

- (NSString *)timeStringWithDate:(NSDate *)date
{
    
    NSDateFormatter *dateForm = [[NSDateFormatter alloc] init];
    
    dateForm.dateFormat = @"yyyy-MM-dd  HH:mm:ss";
    
    NSString *timeStr = [dateForm stringFromDate:date];
    
    return timeStr;
}