带有 Spring 表达式的 ExpandoObject

Question

我使用 ExpandoObject 类创建对象，我想对该对象执行 spring.net 表达式，但随后出现以下错误：

“名称”节点无法为指定的上下文解析 [System.Dynamic.ExpandoObject]。

代码如下：

  dynamic expandObject = new ExpandoObject();
  expandObject.Name = "Los";
  var value = (string)ExpressionEvaluator.GetValue(expandObject, "Name");

我认为 spring 表达式不适用于动态对象，但也许你现在为什么会发生这种情况以及任何解决方法（我尝试在 IDictionary 列表上转换 ExpandoObject 然后执行 spring 表达式，但这不起作用）？

Answer 1

我下载了Spring.Net源代码，首先注意到spring.net核心库是用.Net framework 2.0制作的，因为当前版本（1.3.2）的spring.net不能工作使用 System.Dynamic.ExpandoObject（在 .net framework 4.0 中添加）。
正如我们现在的 System.Dynamic.ExpandoObject 是一个对象，其成员可以在运行时动态添加和删除，添加的属性和方法保存在 Dictionary 列表中。因此，我修改了 spring.net core 的源代码以支持 System.Dynamic.ExpandoObject，现在一切正常。


我改变了什么？
1. 我将 Spring.Net 库升级到 .NET framework 4.0
2.我在Spring.Expressions.PropertyOrFieldNode类中修改了InitializeNode()方法：

private void InitializeNode(object context)
    {
        Type contextType = (context == null || context is Type ? context as Type : context.GetType());

        if (accessor == null || accessor.RequiresRefresh(contextType))
        {
            memberName = this.getText();

            // clear cached member info if context type has changed (for example, when ASP.NET page is recompiled)
            if (accessor != null && accessor.RequiresRefresh(contextType))
            {
                accessor = null;
            }

            // initialize this node if necessary
            if (contextType != null && accessor == null)
            {//below is new IF;)
                if (contextType == typeof(System.Dynamic.ExpandoObject))
                {
                    accessor = new ExpandoObjectValueAccessor(memberName);
                }
                // try to initialize node as enum value first
                else if (contextType.IsEnum)
                {
                    try
                    {
                        accessor = new EnumValueAccessor(Enum.Parse(contextType, memberName, true));
                    }
                    catch (ArgumentException)
                    {
                        // ArgumentException will be thrown if specified member name is not a valid
                        // enum value for the context type. We should just ignore it and continue processing,
                        // because the specified member could be a property of a Type class (i.e. EnumType.FullName)
                    }
                }

                // then try to initialize node as property or field value
                if (accessor == null)
                {
                    // check the context type first
                    accessor = GetPropertyOrFieldAccessor(contextType, memberName, BINDING_FLAGS);

                    // if not found, probe the Type type
                    if (accessor == null && context is Type)
                    {
                        accessor = GetPropertyOrFieldAccessor(typeof(Type), memberName, BINDING_FLAGS);
                    }
                }
            }

            // if there is still no match, try to initialize node as type accessor
            if (accessor == null)
            {
                try
                {
                    accessor = new TypeValueAccessor(TypeResolutionUtils.ResolveType(memberName));
                }
                catch (TypeLoadException)
                {
                    if (context == null)
                    {
                        throw new NullValueInNestedPathException("Cannot initialize property or field node '" +
                                                                 memberName +
                                                                 "' because the specified context is null.");
                    }
                    else
                    {
                        throw new InvalidPropertyException(contextType, memberName,
                                                           "'" + memberName +
                                                           "' node cannot be resolved for the specified context [" +
                                                           context + "].");
                    }
                }
            }
        }
    }

2. 我添加了我的自定义 ExpandoObjectValueAccessor

private class ExpandoObjectValueAccessor : BaseValueAccessor
    {
        private string memberName;

        public ExpandoObjectValueAccessor(string memberName)
        {
            this.memberName = memberName;
        }

        public override object Get(object context)
        {
            var dictionary = context as IDictionary<string, object>;

            object value;
            if (dictionary.TryGetValue(memberName, out value))
            {
                return value;
            }
            throw new InvalidPropertyException(typeof(System.Dynamic.ExpandoObject), memberName,
                                               "'" + memberName +
                                               "' node cannot be resolved for the specified context [" +
                                               context + "].");
        }

        public override void Set(object context, object value)
        {
            throw new NotSupportedException("Cannot set the value of an expando object.");
        }
    }

编辑：当然，您不必将 spring.net 核心库升级到 .net framework 4.0 - 我这样做是因为我不喜欢通过魔术字符串来组合对象类型，我更喜欢使用 typeof()