调用扩展方法(TreeNodeCollection Add方法)的正确方法是什么? [英] What is the correct way to call an extension method (TreeNodeCollection Add method)?

问题描述

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)'

The pertinent parts of my code are below. In the MyTreeView class (last block of code below), the line of code TncExtensions.TncNodeAdd(this, myTreeViewNode); generates the error 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?

Why can't the compiler figure out what the 2nd formal parameter is for my TreeNodeCollection extension method?

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);
    }
}

推荐答案

我相信您创建的扩展方法没有多大用处，但是如果您想知道问题出在哪里，则说明您使用了错误的扩展方法.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:

I believe the extension method which you created is not of much use but if you are curious to know what the problem is, you are using the extension method wrong. You are accessing it like a static method, in this style you need to pass 3 arguments based on the signature of the method:

TncExtensions.TncNodeAdd(Nodes, this, myTreeViewNode);

或者像扩展方法一样使用它:

Or use it like an extension method:

this.Nodes.TncNodeAdd(this, myTreeViewNode);

我建议您将扩展方法更改为:

I suggest you change the extension method to:

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

要了解更多信息，请查看

To learn more, take a look at Extension Methods.

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