IQueryable转换为 IList;
设置
public interface ITable { }
public class Company : ITable {
public int Id { get; set; }
public string Name { get; set; }
}
public class PaginationGridModel {
public PaginationGridModel(IList<ITable> rows) {
//cool stuff goes here
}
}
public GridModel GenerateModel<T>(IQueryable<T> Table) where T : ITable {
return new GridModel((IList<ITable>)Table);
}
//Actual Call
return GenerateModel<Company>(this.dataContext.Companies);
异常生成的
Unable to cast object of type 'System.Collections.Generic.List`1[Company]' to type 'System.Collections.Generic.IList`1[ITable]'.
问题
由于 Company 实现了 ITable 我应该能够将我的 List 转换为 IListT。但 T 在函数定义中被限制为 ITable。我在这里做错了什么？当我不使用泛型时，设置工作得很好。不过，我想要一个通用设置，因为我一直在一遍又一遍地编写相同的代码 - 这很糟糕:)
任何帮助将不胜感激。即使你告诉我这是不可能的。
Setup
public interface ITable { }
public class Company : ITable {
public int Id { get; set; }
public string Name { get; set; }
}
public class PaginationGridModel {
public PaginationGridModel(IList<ITable> rows) {
//cool stuff goes here
}
}
public GridModel GenerateModel<T>(IQueryable<T> Table) where T : ITable {
return new GridModel((IList<ITable>)Table);
}
//Actual Call
return GenerateModel<Company>(this.dataContext.Companies);
Exception Generated
Unable to cast object of type 'System.Collections.Generic.List`1[Company]' to type 'System.Collections.Generic.IList`1[ITable]'.
Question
Since Company implements ITable I should be able to convert my List<Company> into an IList<ITable> however it doesn't want to work because it's actually T. But T is constrained in the function definition to an ITable. What am I doing wrong here? When I'm not using Generics the setup works just fine. However I wanted a Generic setup because I've been writing the same code over and over - which is bad :)
Any help would be greatly appreciated. Even if what you tell me is that it can't be done.
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对于.NET 3.5，你可以使用这个：
For .NET 3.5 you can use this:
如果这是 .NET 4.0，您可以阅读有关通用协变和逆变的内容。
If this is .NET 4.0 you could read about generic covariance and contravariance.
您还可以使用 LINQ Cast() 扩展方法：
这更清晰一些。
此外，如果可能的话，使用 IEnumerable 而不是 IList 通常会更好。
You can also use the LINQ Cast() extension method:
which is a bit clearer.
Also it is often nicer to use IEnumerable instead of IList when possible.