1

我有以下课程：

namespace CommonInterfaces
{
    public interface INode
    {
        int? ParentNodeId { get; set; }
        int? ChildNodeId { get; set; }
    }
}

public class FieldDependencyModel : DataModel<int>, ICacheable
{

    #region Field

    private int _FieldDependencyId;
    private int? _FieldId;
    private int? _FieldParentId;

    #endregion  

    #region Properties

    public virtual int FieldDependencyId
    {
        get { return getPropertyValue("FieldDependencyId",_FieldDependencyId); }
        set { _FieldDependencyId = value; }
    }

    public virtual int? ChildNodeId
    {
        get { return getPropertyValue("FieldId",_FieldId); }
        set { _FieldId = value; }
    }

    public virtual int? ParentNodeId
    {
        get { return getPropertyValue("FieldParentId",_FieldParentId); }
        set { _FieldParentId = value; }
    }

    #endregion
}


    public interface IFieldDependencyService
    {
        IList<FieldDependency> GetAllFieldDependencies();
    }

    public class FieldDependency : FieldDependencyModel, INode
    {
    }


    public class FieldDependencyDataService : BaseDataService, IFieldDependencyService
    {
        public FieldDependencyDataService(DataAccessHandle serviceHandler) : base(serviceHandler) {}

        public IList<FieldDependency> GetAllFieldDependencies()
        {
            return _accessService.loadAll<FieldDependency>();
        }
    }

    public class TreeService
    {
        private IList<INode> _relationships;
        private INode _rootNode;    


        public TreeService(INode rootNode, IList<INode> nodeRelationships)
        {
            _relationships = nodeRelationships;
            _rootNode = rootNode;
        }


        public Tree<INode> BuildTree()
        {
            Tree<INode> tree;

            tree = new Tree<INode>(_rootNode, _relationships);

            return tree;
        }
    }

我尝试发送一个隐含 INode 的类型，当我尝试将 fieldDependencies 传递给新的 TreeService 实例时，它仍然显示以下错误：

Error   5   Argument 2: cannot convert from 'System.Collections.Generic.IList<FieldDependency>' to 'System.Collections.Generic.IList<CommonInterfaces.INode>'

这是我收到此错误的调​​用代码：

            IList<FieldDependency> fieldDependencies = _service.GetAllFieldDependencies();

            FieldDependency rootDependency = fieldDependencies.First(d => d.ParentNodeId == null);
 var service = new TreeService(rootDependency, fieldDependencies); // fails here, doesn't like fieldDependencies
4

4 回答 4

1

试试这个

IList<INode> fieldDependencies = _service.GetAllFieldDependencies()
.First(d => d.ParentNodeId == null).Select(d => (INode)d);
于 2013-04-01T06:12:16.660 回答
1

您不能这样做，因为您正在尝试将 an 转换IList<FieldDependency>为 an IList<INode>，因此您尝试转换的实际对象是将IList相关类型作为其泛型类型的对象。您可以采取一些措施来解决这个问题。

替换IList<FieldDependency>为IList<INode>

您可以更改您的代码，使其IList<FieldDependency>成为IList<INode>.

public interface IDataFieldDependencyService
{
    IList<INode> GetAllFieldDependencies();
}

public class FieldDependencyDataService : BaseDataService, IFieldDependencyService
{
    public FieldDependencyDataService(DataAccessHandle serviceHandler) : base(serviceHandler) {}

    public IList<INode> GetAllFieldDependencies()
    {
        return _accessService.loadAll<FieldDependency>();
    }
}

用法

IList<INode> fieldDependencies = _service.GetAllFieldDependencies();

INode rootDependency = fieldDependencies.First(d => d.ParentNodeId == null);
var service = new TreeService(rootDependency, fieldDependencies);

Select并转换为INode

您还可以从中选择所有元素_service.GetAllFieldDependencies()并将它们装箱INode。

IList<INode> fieldDependencies = _service.GetAllFieldDependencies()
    .Select(e => (INode)e)
    .ToList();

INode rootDependency = fieldDependencies.First(d => d.ParentNodeId == null);
var service = new TreeService(rootDependency, fieldDependencies);

协方差

如果您使用s ，那么您可能可以使用协方差（我相信.NET 4）IEnumerable做您想做的事情。

public class TreeService
{
    private IEnumerable<INode> _relationships;
    private INode _rootNode;    


    public TreeService(INode rootNode, IEnumerable<INode> nodeRelationships)
    {
        _relationships = nodeRelationships;
        _rootNode = rootNode;
    }


    public Tree<INode> BuildTree()
    {
        Tree<INode> tree;

        tree = new Tree<INode>(_rootNode, _relationships);

        return tree;
    }
}

用法

IEnumerable<INode> fieldDependencies = _service.GetAllFieldDependencies();

INode rootDependency = fieldDependencies.First(d => d.ParentNodeId == null);
var service = new TreeService(rootDependency, fieldDependencies);
于 2013-04-01T06:13:23.297 回答
0

您已将字段依赖项定义为 FieldDependency 列表，即

fieldDependencies.GetType() == typeof<IList<FieldDependency>>

TreeService 构造函数的第二个参数期望tyepof(IList<INode>>)

你应该能够改变你定义变量 fieldDependencies 的方式IList<INode>

IE

IList<INode> fieldDependencies = _service.GetAllFieldDependencies()

于 2013-04-01T06:15:20.450 回答
0

尝试

var service = new TreeService(rootDependency, fieldDependencies.Cast<INode>().ToList());

从类 A 派生类 B 并不能保证您能够将具有类型参数 B 的对象泛型集合类型转换为具有类型参数 A 的泛型集合类型。

您可以在此处和此处阅读有关逆变的更多信息。

于 2013-04-01T06:17:24.670 回答