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I have a model, deserialized from XML, in which all node objects derive from the same base class, and nodes can be nested (somewhat) arbitrarily. I am trying to write a collection of modules which can translate a loaded model into various text based formats. I thought it would be nifty if each such module was an extension class which would allow me to simply call Model.ToText(), Model.ToHtml(), etc. But I am running into some problems.

Here is a simplified example:

using System;
using System.Collections.Generic;
using System.Text;

namespace Sample
{
    public abstract class Foo
    {
    }

    public class Bar : Foo
    {
        public List<Foo> Children = new List<Foo>();
        public int Qux;
    }

    public class Baz : Foo
    {
        public string Quux;
    }

    public static class Extension
    {
        public static string ToText(this Foo foo, int indent = 0)
        {
            return String.Format("{0}Foo <>\n", new String(' ', indent));
        }

        public static string ToText(this Bar bar, int indent=0)
        {
            StringBuilder sb = new StringBuilder(); 
            sb.Append(String.Format("{0}Bar <Qux={1}>\n", new String(' ', indent), bar.Qux));
            foreach (var child in bar.Children)
            {
                sb.Append(child.ToText(indent + 1));
            }
            return sb.ToString();
        }

        public static string ToText(this Baz baz, int indent=0)
        {
            return String.Format("{0}Baz <Quux={1}>\n", new String(' ', indent), baz.Quux);
        }

    }

    class Program
    {
        static void Main(string[] args)
        {
            Baz baz = new Baz { Quux = "frob" };

            Bar bar = new Bar
                {
                    Children = new List<Foo>()
                        {
                            new Baz {Quux = "fred"},
                            new Bar
                                {
                                    Qux = 11,
                                    Children = new List<Foo>()
                                        {
                                            new Baz() {Quux = "flog"}
                                        }
                                }
                        }
                };

            //This works
            Console.WriteLine(baz.ToText());

            //But this doesn't
            Console.WriteLine(bar.ToText());
            Console.ReadKey();
        }
    }
}

If I run this I get:

Baz <Quux=frob>

Bar <Qux=0>
 Foo <>
 Foo <>

If I try and get tricky and do this instead:

public static string ToText(this Foo foo, int indent = 0)
{
    return ((dynamic)foo).ToText(indent);
}

... the first print works, but the second gives me the exception:

{"'Sample.Baz' does not contain a definition for 'ToText'"}

I am probably taking the wrong approach entirely, but I could use some direction.

4

1 に答える 1

1

少しつまずいた後、仮想拡張メソッドのトピックを見つけましたか? . ビジターパターンでこれをきれいに解決できるようです：

public interface IFooFormater
{
    string Format(Foo foo, int indent);
    string Format(Bar bar, int indent);
    string Format(Baz baz, int indent);
}

public class FooFormater : IFooFormater
{
    public string Format(Foo foo, int indent)
    {
        return "";
    }

    public string Format(Bar bar, int indent)
    {
        StringBuilder sb = new StringBuilder();
        sb.Append(String.Format("{0}Bar <Qux={1}>\n", new String(' ', indent), bar.Qux));
        foreach (var child in bar.Children)
        {
            sb.Append(this.Format((dynamic)child , indent + 1));
        }
        return sb.ToString();            
    }

    public string Format(Baz baz, int indent)
    {
        return String.Format("{0}Baz <Quux={1}>\n", new String(' ', indent), baz.Quux);
    }
}


public static class Extension
{

    public static string ToText(this Foo foo, IFooFormater fooFormater)
    {
        return fooFormater.Format((dynamic)foo, 0);
    }
}

次に、次のように呼び出します。

IFooFormater fooFormater = new FooFormater();
Console.WriteLine(bar.ToText(fooFormater));

期待される出力が得られます。

Bar <Qux=0>
 Baz <Quux=fred>
 Bar <Qux=11>
  Baz <Quux=flog>
于 2013-07-18T08:06:40.657 に答える