asp.net-mvc – MVC帖子没有填充模型

根据this answer on model with collection not populating on postback

In other words,(…) If any required fields are missing,or if the values are
submitted in such a way that they cannot be converted to the type of a required field,then the entire object will be left null

我已经更改了几种值类型,但我无法使其工作.

这是我的模型：

public class AddModel
{
    //Get properties 
    public Vehicle vehicle; 

    //Post properties 
    [Required(ErrorMessage = "Please enter a start date")]
    public DateTime StartDate; 
    public int? StatusCode; 

    public SelectList StatusCodes()
    {
         ...
    } 
}

你能想到为什么它没有被填充吗？