自定义ExpressionBuilder

ExpressionBuilder的常见说明见https://msdn.microsoft.com/zh-cn/library/System.Web.Compilation.ExpressionBuilder(v=vs.80).aspx

下面贴代码：

编写自定义ExpressionBuilder用于翻译，翻译文件缓存依赖。

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.ComponentModel;
using System.Web.Compilation;
using System.Web.UI;
using System.CodeDom;
using System.Web.Hosting;
using System.Web.Caching;
using System.Xml;

namespace ExpressionBuilderTest.Library
{
    /// <summary>
    /// 自定义ExpressionBuilder
    /// </summary>
    public class SPExpressionBuilder:ExpressionBuilder
    {
        // Create a method that will return the result
        // set for the expression argument.
        public static object GetEvalData(string expression, Type target, string entry)
        {
            XmlDocument doc = (XmlDocument)HostingEnvironment.Cache["transDoc"];
            if (doc == null)
            {
                doc = new XmlDocument();
                string filePath = HostingEnvironment.MapPath("~/Translate.config");
                doc.Load(filePath);
                CacheDependency fileDep = new CacheDependency(filePath);
                HostingEnvironment.Cache.Insert("transDoc", doc,fileDep);
            }
            XmlNode xn = doc.SelectSingleNode(string.Format("/configuration/p[@key='{0}']",expression));
            if (xn != null)
            {
                return ((XmlElement)xn).GetAttribute("value");
            }
            return expression;
        }

        public override object EvaluateExpression(object target, BoundPropertyEntry entry,
                object parsedData, ExpressionBuilderContext context)
        {
            return GetEvalData(entry.Expression, target.GetType(), entry.Name);
        }

        public override CodeExpression GetCodeExpression(BoundPropertyEntry entry,
                object parsedData, ExpressionBuilderContext context)
        {
            Type type1 = entry.DeclaringType;
            PropertyDescriptor descriptor1 = TypeDescriptor.GetProperties(type1)[entry.PropertyInfo.Name];
            CodeExpression[] expressionArray1 = new CodeExpression[];
            expressionArray1[] = new CodePrimitiveExpression(entry.Expression.Trim());
            expressionArray1[] = new CodeTypeOfExpression(type1);
            expressionArray1[] = new CodePrimitiveExpression(entry.Name);
            return new CodeCastExpression(descriptor1.PropertyType, new CodeMethodInvokeExpression(new
           CodeTypeReferenceExpression(base.GetType()), "GetEvalData", expressionArray1));
        }

        public override bool SupportsEvaluate
        {
            get { return true; }
        }
    }
}

翻译文件为Translate.config.格式如下：

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <p key="_welCom_" value="You Are Welcome!"/>
</configuration>

好了，现在在web.config里配置就可以使用了。web.config配置如下：

<?xml version="1.0" encoding="utf-8"?>

<configuration>
    <system.web>
      <compilation debug="true" targetFramework="4.0">
        <expressionBuilders>
          <add expressionPrefix="SPExpression"
           type="ExpressionBuilderTest.Library.SPExpressionBuilder"/>
        </expressionBuilders>
      </compilation>
    </system.web>

</configuration>

在页面上拖一个label

<asp:Label ID="Label1" runat="server" Text="<%$SPExpression:_welCom_ %>"></asp:Label>

即可实现翻译。