.NET 动态类属性

Question

实际上，我尝试设计某种电子商店。 我对从管理面板（运行时）创建多种产品感兴趣。

例如我有基本的产品类

public class Product
{ 
     public double Price {get;set;}
}

我想创建一些具有 ScreenDiagonal 的电视类

public class TV : Product
{ 
     public int ScreenDiagonal {get;set;}
}

但我需要在运行时创建这样的类，并为其设置属性。 这样做的最佳做法是什么？反思或其他一些想法？

Answer 1

使用 CodeDom，像这样：

using System;
using System.Collections.Generic;
using System.Linq;
using Microsoft.CSharp;
using System.CodeDom.Compiler;
using System.CodeDom;

namespace Test
{
    class Program
    {
        static void Main(string[] args)
        {
            string className = "BlogPost";

            var props = new Dictionary<string, Type>() {
                { "Title", typeof(string) },
                { "Text", typeof(string) },
                { "Tags", typeof(string[]) }
            };

            createType(className, props);
        }

        static void createType(string name, IDictionary<string, Type> props)
        {
            var csc = new CSharpCodeProvider(new Dictionary<string, string>() { { "CompilerVersion", "v4.0" } });
            var parameters = new CompilerParameters(new[] { "mscorlib.dll", "System.Core.dll"}, "Test.Dynamic.dll", false);
            parameters.GenerateExecutable = false;

            var compileUnit = new CodeCompileUnit();
            var ns = new CodeNamespace("Test.Dynamic");
            compileUnit.Namespaces.Add(ns);
            ns.Imports.Add(new CodeNamespaceImport("System"));

            var classType = new CodeTypeDeclaration(name);
            classType.Attributes = MemberAttributes.Public;
            ns.Types.Add(classType);

            foreach (var prop in props)
            {
                var fieldName = "_" + prop.Key;
                var field = new CodeMemberField(prop.Value, fieldName);
                classType.Members.Add(field);

                var property = new CodeMemberProperty();
                property.Attributes = MemberAttributes.Public | MemberAttributes.Final;
                property.Type = new CodeTypeReference(prop.Value);
                property.Name = prop.Key;
                property.GetStatements.Add(new CodeMethodReturnStatement(new CodeFieldReferenceExpression(new CodeThisReferenceExpression(), fieldName)));
                property.SetStatements.Add(new CodeAssignStatement(new CodeFieldReferenceExpression(new CodeThisReferenceExpression(), fieldName), new CodePropertySetValueReferenceExpression()));
                classType.Members.Add(property);
            }

            var results = csc.CompileAssemblyFromDom(parameters,compileUnit);
            results.Errors.Cast<CompilerError>().ToList().ForEach(error => Console.WriteLine(error.ErrorText));
        }
    }

它创建一个包含此类的程序集“Test.Dynamic.dll”

namespace Test.Dynamic
{
    public class BlogPost
    {
        private string _Title;
        private string _Text;
        private string[] _Tags;

        public string Title
        {
            get
            {
                return this._Title;
            }
            set
            {
                this._Title = value;
            }
        }
        public string Text
        {
            get
            {
                return this._Text;
            }
            set
            {
                this._Text = value;
            }
        }
        public string[] Tags
        {
            get
            {
                return this._Tags;
            }
            set
            {
                this._Tags = value;
            }
        }
    }
}

你也可以使用 C# 的动态特性

DynamicEntity 类，运行时无需创建任何东西

public class DynamicEntity : DynamicObject
{
    private IDictionary<string, object> _values;

    public DynamicEntity(IDictionary<string, object> values)
    {
        _values = values;
    }
    public override bool TryGetMember(GetMemberBinder binder, out object result)
    {
        if (_values.ContainsKey(binder.Name))
        {
            result = _values[binder.Name];
            return true;
        }
        result = null;
        return false;
    }
}

并像这样使用它

var values = new Dictionary<string, object>();
values.Add("Title", "Hello World!");
values.Add("Text", "My first post");
values.Add("Tags", new[] { "hello", "world" });

var post = new DynamicEntity(values);

dynamic dynPost = post;
var text = dynPost.Text;