/*

动态编译类，可以计算表达式，也可以调用系统中的类

调用方式：     return new XXXXXXX.Eval().GetValue("System.DateTime.Now")

返回结果：     2005-08-04 15:00:24

*/
using System;
using System.CodeDom;
using System.CodeDom.Compiler;
using Microsoft.CSharp;
using System.Reflection;
using System.IO;

namespace XXXXXXX
{
 /*****************************************************************
 ** 文件名:       Eval.cs
 ** Copyright (c) 1999 -2003
 ** 创建人:       Phoenix
 ** 创建日期:
 ** 修改人:   BigmouthZ@163.net
 ** 修改日期: 2005/08/04
 ** 描 述:         获取字符串所表示的逻辑意义
 ** 版 本:1.0
 ******************************************************************/
 public class Eval
 {
  public object GetValue( string value )
  {
   string codeSnippet =
@"
using System;
using System.Collections;
using DBCore;namespace CzG
{
 public class $0$
 {
  public $0$(){}
  public object GetValue()
  {
   return $1$ ;
  }
 }
}";
   string tmp = "Eval" + Convert.ToString(System.DateTime.Now.Ticks);
   codeSnippet = codeSnippet.Replace("$0$",tmp);
   codeSnippet = codeSnippet.Replace("$1$",value);
   object b = "";
   try
   {
    ICodeCompiler compiler =  new CSharpCodeProvider().CreateCompiler();
    CompilerParameters para = new CompilerParameters();
    para.ReferencedAssemblies.Add( "System.dll" );
    string path = System.Environment.CurrentDirectory;
para.ReferencedAssemblies.Add( path + @"\DBCore.dll" );    para.GenerateInMemory = true;
    para.GenerateExecutable = false;
    para.OutputAssembly = path + "\\" + tmp + ".dll";

CompilerResults cr = compiler.CompileAssemblyFromSource(para, codeSnippet);
    Assembly asm = cr.CompiledAssembly;
  
    object obj = asm.CreateInstance( "CzG." + tmp );
    Type type = asm.GetType( "CzG." + tmp );
    MethodInfo mi = type.GetMethod("GetValue"); 
    
    b =  mi.Invoke( obj , null );
    GC.Collect();
    System.IO.File.Delete( path + "\\" + tmp + ".dll");
   }
   catch
   {
    b = "CallError!";
   }

return b;
  }
 }
}