Question

我有这个基类，我创建了一个Media（List）列表

public abstract class Media 
{

    #region Fields

    private DateTime? _releaseDate;

    #endregion

    #region Constructor
    public Media() 
    {

    }
    #endregion

    #region Properties
    //Used to convert the Json propertyname
    [Key]
    public int MediaId { get; set; }

    [JsonProperty(PropertyName = "id")]
    public int ApiId { get; set; }

    [JsonProperty(PropertyName = "title")]
    [MaxLength(200), MinLength(0)]
    public virtual string Title { get; set; }


    [JsonProperty(PropertyName = "overview")]
    [MaxLength(10000), MinLength(0)]
    public string Plot { get; set; }


    //Todo definer lengths
    [JsonProperty(PropertyName = "poster_path")]
    [MaxLength(200), MinLength(0)]
    public string Image { get; set; }

    [JsonProperty(PropertyName = "status")]
    [MaxLength(30), MinLength(0)]
    public string Status { get; set; }


    [JsonProperty(PropertyName = "release_date")]
    public virtual DateTime? ReleaseDate 
    { 
        get { return _releaseDate; }
        set 
        {
            _releaseDate = value;
        }

    }

    public int TotaltRating { get; set; }
    public int AmountOfRaters { get; set; }
    public double CurrentRating { get; set; }

    [JsonProperty(PropertyName = "genres")]
    public virtual List<Genre> GenresInMedia { get; set; }


    public virtual List<Actor> ActorsInMedia { get; set; }

    public virtual List<Tag> TagsInMedia { get; set; }


    public virtual List<Reviewer> SeenBy { get; set; }
    #endregion
}

然后我有这个子类（我还有一些其他的子类，但是没有在这里粘贴它们）

public class Movie : Media
{

    [JsonProperty(PropertyName = "budget")]
    public int Budget { get; set; }

    [JsonProperty(PropertyName = "tagline")]
    [MaxLength(1000), MinLength(0)]
    public string Tagline { get; set; }

    [NotMapped]
    public List<Trailer> Trailers { get; set; }

}

这是我试图实现的代码。

List<Media> MediaList = new List<Media>();
List<Movie> MovieList = new List<Movie>();
MovieList.Add(new Movie());
MovieList.Add(new Movie());
MovieList.Add(new Movie());

MediaList.AddRange(MovieList);

这给了我一个NullReferenceException

MediaList.AddRange(MovieList.Cast<Media>().ToList());

这也给了我一个NullReferenceException ..

如何将电影列表转换为媒体列表？它似乎不起作用..

提前致谢。

Answer 1

必须有其他事情发生。我复制了你的代码并运行了这个......

public abstract class Media
{
    #region Fields

    private DateTime? _releaseDate;

    #endregion

    #region Constructor
    public Media() 
    {

    }
    #endregion

    #region Properties
    //Used to convert the Json propertyname
    [Key]
    public int MediaId { get; set; }

    [JsonProperty(PropertyName = "id")]
    public int ApiId { get; set; }

    [JsonProperty(PropertyName = "title")]
    [MaxLength(200), MinLength(0)]
    public virtual string Title { get; set; }


    [JsonProperty(PropertyName = "overview")]
    [MaxLength(10000), MinLength(0)]
    public string Plot { get; set; }

    #endregion
}

public class Movie : Media
{
    [JsonProperty(PropertyName = "budget")]
    public int Budget { get; set; }

    [JsonProperty(PropertyName = "tagline")]
    [MaxLength(1000), MinLength(0)]
    public string Tagline { get; set; }

    //[NotMapped]
    //public List<Trailer> Trailers { get; set; }
}

然后

List<Media> MediaList = new List<Media>();
List<Movie> MovieList = new List<Movie>();
MovieList.Add(new Movie());
MovieList.Add(new Movie());
MovieList.Add(new Movie());

MediaList.AddRange(MovieList);

MediaList.AddRange(MovieList.Cast<Media>().ToList());

工作得很好。 MediaList中有6个元素。

我不得不评论Trailer，因为你没有提供。

父列表中的多态性子列表

1 个答案: