c# - Linq 转换为列表

Question

我有以下类(class):

public class Column
{
    public String Name;
    public String Value;
}

public class ColumnList : List<Column> {}

然后我做:

var cols = (from c in othercolumnlist
            select new Column
            {
               Name = c.Name,
            }).ToList() as ColumnList;

但是它返回空值。我怎样才能成功地转换到我的名单中？

Answer 1

ColumnList是 List<Column>但是List<Column>不是 ColumnList .考虑 Animal和 Dog类:

public class Animal
{
}

public class Dog: Animal
{
}

你要做的是把任何动物都当作狗来对待。但并非所有动物都是狗。可以有 Cat或 Kangaroo .这就是为什么 as ColumnList返回 null .

您需要创建新的 ColumnList改为实例并手动向其添加列:

var columnList = new ColumnList();
columnList.AddRange(othercolumnlist.Select(c => new Column { Name = c.Name }));

---

如果您需要经常这样做，那么您可以将静态创建方法添加到您的ColumnList类:

public static ColumnList CreateFrom(ColumnList other)
{
     var columnList = new ColumnList();
     columnList.AddRange(other.Select(c => new Column { Name = c.Name }));
     return columnList;
}

并以这种方式使用它:

var columnList = ColumnList.CreateFrom(otherColumnList);