Inheritance 與 generics 接口

Question

我正在嘗試遷移一個必須從各種 XML 讀取的應用程序，在將它們持久化到數據庫之前，它們每個都有不同的模型和方法/東西要做。 出於這個原因，我決定創建一個接口IEntityController<T> where T: PersistentEntity和一個 controller 為每個實體（XML）實現它，這樣它們都可以有不同的實現......

    public interface IEntityController<T> where T : PersistentEntity
{
    /// <summary>
    /// Check if the data inserted into the xml is valid and all the requirements are met
    /// </summary>
    /// <exception cref="FooValidationException">When the instance is not valid and can't be saved</exception>
    void Validate(T entity);

    /// <summary>
    /// Implement changes in data before its saved
    /// </summary>
    void PreProcess(T entity);

    /// <summary>
    /// Save or Update the entity
    /// </summary>
    /// <exception cref="System.Data.SqlClient.SqlException"></exception>
    void Persist(T entity);

    /// <summary>
    /// Implement changes in data after the entity is saved
    /// </summary>
    void PostProcess(T entity);
}

之后，我有一個工廠方法，它基於 xml 返回正確的 controller：

        private IEntityController<PersistentEntity> GetController(XmlFile file)
    {
        Type fileType = file.GetType();

        if(fileType == typeof(FileBoo))
            return (IEntityController<PersistentEntity>) new BooController(DC);
      ......
    }

我的問題是： BooController實現了IEntityController<Boo>的接口，其中Boo繼承了PersistentEntity ，當嘗試將 controller 轉換為IEntityController<PersistentEntity>我得到一個InvalidCastException ，盡管我沒有問題將 BooController 轉換為IEntityController<Boo> ，就像 ZD7EFA19FBE7D3977244FBE7D39724忽略泛型類型的 inheritance。

關於如何解決這個/更好地實施它的任何想法？ 謝謝

Answer 1

您可以做的最簡單的事情是從 IEntityController 中刪除泛型類型，使其看起來像這樣：

 public interface IEntityController
{
    /// <summary>
    /// Check if the data inserted into the xml is valid and all the requirements are met
    /// </summary>
    /// <exception cref="FooValidationException">When the instance is not valid and can't be saved</exception>
    void Validate(PersistentEntity entity);

    /// <summary>
    /// Implement changes in data before its saved
    /// </summary>
    void PreProcess(PersistentEntity  entity);

    /// <summary>
    /// Save or Update the entity
    /// </summary>
    /// <exception cref="System.Data.SqlClient.SqlException"></exception>
    void Persist(PersistentEntity entity);

    /// <summary>
    /// Implement changes in data after the entity is saved
    /// </summary>
    void PostProcess(PersistentEntity  entity);
}

由於你的方法

private IEntityController<PersistentEntity> GetController(XmlFile file)

總是返回 PersistentEntity 的 IEntityController 而不是 T 的 IEntityController 你根本不需要 generics 。

記住：

List<string> doesn't inherit from List<object>

否則這可能會發生

public static void DestroyTheWorld(List<object> list) {
    list.add(new object());
}

public static void Main() {
    var list = new List<string>();
    DestroyTheWorld(list); //possible if list<string> inherits from list<object>
    //an object has been added to a list of string
}