Question

以下是我要完成的示例：

public class BaseClass<T>
{
    public static T GetByID(int ID)
    {
        // Need database name here that is determined at design time in the derived class.
        var databaseName = "";
        // do some stuff involving database name that gets me object by ID here.
        return default(T);
    }
}
public class DerivedClass : BaseClass<DerivedClass>
{
    private string DatabaseName { get; set; }
}

基本上，我如何在基类静态GetByID方法中访问派生的“DatabaseName”？

编辑：发布此内容之后，我又尝试了一件事。我之前玩过属性，但失败了，但我认为我的大脑是糊状的。刚刚再次尝试并进行了测试，它正在运行。这是更新的样本。

public class BaseClass<T>
{
    public static T GetByID(int ID)
    {
        // Need database name here that is determined at design time in the derived class.
        var databaseName = ((DatabaseAttribute)typeof(T).GetCustomAttributes(typeof(DatabaseAttribute), true).First()).DatabaseName;
        // do some stuff involving database name that gets me object by ID here.
        return default(T);
    }
}
[Database("MyDatabase")]
public class DerivedClass : BaseClass<DerivedClass>
{

}
public class DatabaseAttribute : Attribute
{
    public DatabaseAttribute(string databaseName)
    {
        DatabaseName = databaseName;
    }
    public string DatabaseName { get; set; }
}

Answer 1

派生类的基类是单向继承：基类不知道派生类的存在，因此无法访问它。

除此之外，您将很难从静态方法访问非静态属性。

Answer 2

我知道你已经回答了自己的问题，但有些改进......

添加where子句以保证继承，这意味着任何静态方法都可以使用继承的方法。如果您希望能够创建继承类的实例，则可能还需要添加new()子句。

public class BaseClass<T> : where T : BaseClass<T>
{

    static readonly string databaseName;


    static BaseClass() {
      // Setup database name once per type of T by putting the initialization in
      // the static constructor

      databaseName = typeof(T).GetCustomAttributes(typeof(DatabaseAttribute),true)
                              .OfType<DatabaseAttribute>()
                              .Select(x => x.Name)
                              .FirstOrDefault();
    }

    public static T GetByID(int ID)
    {
        // Database name will be in the static field databaseName, which is unique
        // to each type of T

        // do some stuff involving database name that gets me object by ID here.
        return default(T);
    }
}

[Database("MyDatabase")]
public class DerivedClass : BaseClass<DerivedClass>
{

}

public class DatabaseAttribute : Attribute
{
    public DatabaseAttribute(string databaseName)
    {
        DatabaseName = databaseName;
    }
    public string DatabaseName { get; set; }
}

如何从基类静态方法访问派生类值？

2 个答案: