Question

下面是我代码的相关部分。在MyTreeView类（下面的最后一个代码块）中，代码行TncExtensions.TncNodeAdd(this, myTreeViewNode);生成错误CS7036 There is no argument given that corresponds to the required formal parameter 'myTreeViewNode' of 'TncExtensions.TncNodeAdd(TreeNodeCollection, MyTreeView_Abstract, MyTreeViewNode_Abstract)'

为什么编译器无法弄清楚我的TreeNodeCollection扩展方法的第二个形式参数是什么？

public static class TncExtensions
{
    public static int TncNodeAdd(this TreeNodeCollection nodes, MyTreeView_Abstract myTreeView, MyTreeViewNode_Abstract myTreeViewNode)
    {
        return myTreeView.Nodes.Add(myTreeViewNode);
    }
}

public abstract class MyTreeViewNode_Abstract : TreeNode
{
    public MyTreeViewNode_Abstract(string text) : base(text)
    {
    }
}

public class MyTreeViewNode : MyTreeViewNode_Abstract
{
    public MyTreeViewNode(string text) : base(text)
    {
    }
}

public abstract class MyTreeView_Abstract : TreeView
{
}

public class MyTreeView : MyTreeView_Abstract
{
    public void CreateTree()
    {
        MyTreeViewNode myTreeViewNode = new MyTreeViewNode("node text");
        TncExtensions.TncNodeAdd(this, myTreeViewNode);
    }
}

Answer 1

我相信您创建的扩展方法没什么用，但是如果您想知道问题出在哪里，那么您使用的扩展方法是错误的。您像访问静态方法一样访问它，以这种方式，您需要根据方法的签名传递3个参数：

TncExtensions.TncNodeAdd(Nodes, this, myTreeViewNode);

或者像扩展方法一样使用它：

this.Nodes.TncNodeAdd(this, myTreeViewNode);

我建议您将扩展方法更改为：

public static int TncNodeAdd(this TreeNodeCollection nodes, MyTreeViewNode_Abstract myTreeViewNode)
{
    return nodes.Add(myTreeViewNode);
}

Answer 2

Reza'a答案仍然是答案，但是为了使我的treenode Add扩展方法有用，我不得不修改对其的调用。我忘记了添加树节点的过程，您需要指定要将新节点附加到的节点集合。

注意：有关所涉及的基本类，请参阅原始问题中的代码

Reza建议的修改后的添加扩展方式

namespace TreeNodeCollectionExtensions
{
    public static class TncExtensions
    {
        public static int Add(this TreeNodeCollection nodes, DRT.DRT_TvwNode_Abstract myTreeViewNode)
        {
            int newNodeIndex = nodes.Add(myTreeViewNode);

            //Do stuff to custom properties that are members of DRT_TvwNode_Abstract and classes derived from DRT_TvwNode_Abstract

            return newNodeIndex;
        }
    }
}

以这种方式使用

using TreeNodeCollectionExtensions;

public class MyTreeView : MyTreeView_Abstract
{
    public MyTreeView() : base()
    {
    }

    public void CreateTree()
    {
        MyTreeViewNode myTreeViewNode;

        //Add node to root of TreeView 
        //Using named parameter to force the compiler to
        //use the Add extension method and not the base Add method
        myTreeViewNode = new MyTreeViewNode("root node text");
        Nodes.Add(myTreeViewNode: myTreeViewNode);

        //Add node one level below root node of TreeView
        //Using named parameter to force the compiler to
        //use the Add extension method and not the base Add method
        myTreeViewNode = new MyTreeViewNode("level 1 node text");
        int newLevel1NodeIndex = Nodes[0].Nodes.Add(myTreeViewNode: myTreeViewNode);

        //Add node one level below level 1 node just created 
        //Using named parameter to force the compiler to
        //use the Add extension method and not the base Add method
        myTreeViewNode = new MyTreeViewNode("level 2 node text");
        int newLevel2NodeIndex = Nodes[0].Nodes[newLevel1NodeIndex].Nodes.Add(myTreeViewNode: myTreeViewNode);

        //etc., etc.

    }
}

调用扩展方法（TreeNodeCollection Add方法）的正确方法是什么？

2 个答案: