如何在C＃2.0中使用匿名通用委托

Question

I have a class called NTree:

class NTree<T>
{

    delegate bool TreeVisitor<T>(T nodeData);

    public NTree(T data)
    {
        this.data = data;
        children = new List<NTree<T>>();
        _stopTraverse = false;
    }

        ...

    public void Traverse(NTree<T> node, TreeVisitor<T> visitor)
    {
        try
        {
            _stopTraverse = false;
            TraverseInternal(node, visitor);
        }
        finally
        {
            _stopTraverse = false;
        }
    }

    private void TraverseInternal(NTree<T> node, TreeVisitor<T> visitor)
    {
        if (_stopTraverse)
            return;

        if (!visitor(node.data))
        {
            _stopTraverse = true;
        }
        foreach (NTree<T> kid in node.children)
            TraverseInternal(kid, visitor);
    }

When I try to use Traverse with anonymous delegate I get:

Argument '2': cannot convert from 'anonymous method' to 'NisConverter.TreeVisitor'

The code:

tTable srcTable = new tTable();
DataRow[] rows;
rootTree.Traverse(rootTree, delegate(TableRows tr)
    {
        if (tr.TableName == srcTable.mappingname)
        {
            rows = tr.Rows;
            return false;
        }
    });

This however produces no errors:

    static bool TableFinder<TableRows>(TableRows tr)
    {
        return true;
    }

...

rootTree.Traverse(rootTree, TableFinder);

I have tried to put "arrowhead-parenthisis" and everything to anonymous delegate but it just does not work. Please help me!

Thanks & BR -Matti

Answer 1

The anonymous delegate you posted lacks the return of a boolean value (most probably the value true when the if(...) guard is false . Thus, it signature is actually void (TableRow) instead of bool (TableRow) , and the compiler is unable to make the conversion.

So the syntax should be:

tTable srcTable = new tTable();  DataRow[] rows;  rootTree.Traverse(rootTree, delegate(TableRows tr) 
    { 
        if (tr.TableName == srcTable.mappingname) 
        { 
            rows = tr.Rows; 
            return false; 
        } 
        return true;
    });

Answer 2

The declaration of TreeVisitor is wrong: it introduces a new type parameter (which conflicts with the declaration of NTree). Just remove the template stuff and you get:

delegate bool TreeVisitor(T nodeData);

Then you can have:

class X
{

    void T()
    {
        NTree<int> nti = new NTree<int>(2);

        nti.Traverse(nti, delegate(int i) { return i > 4; });

    }
}