动态计算字串表达式值的类

最近用到了这个功能，要计算一些字符串表达式，如"1 + 3 / 2"等等，就写了这个类。原理很简单，就是用CodeDom动态生成一个包含自定义函数的程序集，再通过反射调用。网上例子极多。我这个类是拿来就可以用的，只需要Copy一下代码就可以直接用，不用读代码。支持常用数学函数，如Sin，Log等，而且不区分大小写。

using System;
using System.Collections.Generic;
using System.Text;
using System.CodeDom.Compiler;
using Microsoft.VisualBasic;
using System.Reflection;

namespace Ninputer.Utilities
...{
    sealed class Evaluator
    ...{
        private static CodeDomProvider comp = new VBCodeProvider();
        private static CompilerParameters cp = new CompilerParameters();
        private static MethodInfo mi;

        public static object Eval(string expression)
        ...{
            StringBuilder codeBuilder = new StringBuilder();

            codeBuilder.AppendLine("Imports System");
            codeBuilder.AppendLine("Imports System.Math");
            codeBuilder.AppendLine("Imports Microsoft.VisualBasic");
            codeBuilder.AppendLine();
            codeBuilder.AppendLine("Public Module Mode");
            codeBuilder.AppendLine("   Public Function Func() As Object");
            codeBuilder.AppendLine("        Return " + expression);
            codeBuilder.AppendLine("   End Function");
            codeBuilder.AppendLine("End Module");

            cp.ReferencedAssemblies.Add("System.dll");
            cp.ReferencedAssemblies.Add("Microsoft.VisualBasic.dll");
            cp.GenerateExecutable = false;
            cp.GenerateInMemory = true;

            string code = codeBuilder.ToString();
            CompilerResults cr = comp.CompileAssemblyFromSource(cp, code);

            if (cr.Errors.HasErrors)
            ...{
                return null;
            }
            else
            ...{
                Assembly a = cr.CompiledAssembly;
                Type t = a.GetType("Mode");
                //object mode = a.CreateInstance("Mode");
                mi = t.GetMethod("Func", BindingFlags.Static | BindingFlags.Public);
                return mi.Invoke(null, new object[0]);
            }
        }
    }
}

用法也非常简单，实际上除了数学表达式，任何含字面量的有效VB表达式都可以执行。

   
class Program

   
...{
    static void Main(string[] args)
    ...{
        double a = (double)Evaluator.Eval("sin(0.2) + 5");
        Console.WriteLine(a.ToString());
    }
}

注意，我使用的是.NET 2.0的语法，使用.NET 1.1 / VS.NET 2003的请用这段代码：

using System; using System.Text; using System.CodeDom.Compiler; using Microsoft.VisualBasic; using System.Reflection; namespace Ninputer.Utilities {       sealed class Evaluator       {             private static CodeDomProvider comp = new VBCodeProvider();             private static CompilerParameters cp = new CompilerParameters();             private static MethodInfo mi;             public static object Eval(string expression)             {                   StringBuilder codeBuilder = new StringBuilder();                   codeBuilder.AppendLine("Imports System");                   codeBuilder.AppendLine("Imports System.Math");                   codeBuilder.AppendLine("Imports Microsoft.VisualBasic");                   codeBuilder.AppendLine();                   codeBuilder.AppendLine("Public Module Mode");                   codeBuilder.AppendLine(" Public Function Func() As Object");                   codeBuilder.AppendLine(" Return " + expression);                   codeBuilder.AppendLine(" End Function");                   codeBuilder.AppendLine("End Module");                   cp.ReferencedAssemblies.Add("System.dll");                   cp.ReferencedAssemblies.Add("Microsoft.VisualBasic.dll");                   cp.GenerateExecutable = false;                   cp.GenerateInMemory = true;                   string code = codeBuilder.ToString();                   CompilerResults cr = comp.CreateCompiler().CompileAssemblyFromSource(cp, code);                   if (cr.Errors.HasErrors)                   {                         return null;                   }                   else                   {                         Assembly a = cr.CompiledAssembly;                         Type t = a.GetType("Mode");                         //object mode = a.CreateInstance("Mode");                         mi = t.GetMethod("Func", BindingFlags.Static | BindingFlags.Public);                         return mi.Invoke(null, new object[0]);                   }             }       } }