高分请教如何分析表达式树

[artwl_cn]

MSDN官方示例：

// Add the following using directive to your code file:
// using System.Linq.Expressions;
// Create an expression tree.
Expression<Func<int, bool>> exprTree = num => num < 5;
// Decompose the expression tree.
ParameterExpression param = (ParameterExpression)exprTree.Parameters[0];
BinaryExpression operation = (BinaryExpression)exprTree.Body;
ParameterExpression left = (ParameterExpression)operation.Left;
ConstantExpression right = (ConstantExpression)operation.Right;
Console.WriteLine("Decomposed expression: {0} => {1} {2} {3}",
                  param.Name, left.Name, operation.NodeType, right.Value);
// This code produces the following output:
// Decomposed expression: num => num LessThan 5 

但现在的代码却运行不了，请高手指点：

    public class Test
    {
        public void ExpressionTest()
        {
            T t=new T(){ID=1,Name="abc"};
            Expression<Func<T, bool>> exprTree = o => o.ID == t.ID;
            ParameterExpression param = (ParameterExpression)exprTree.Parameters[0];
            BinaryExpression operation = (BinaryExpression)exprTree.Body;
            ParameterExpression left = (ParameterExpression)operation.Left;//这里出错
            ConstantExpression right = (ConstantExpression)operation.Right;

            Console.WriteLine("Decomposed expression:{0}=>{1}{2}{3}",
                param.Name,left.Name,operation.NodeType,right.Value);

        }
    }
    public class T
    {
        public int ID { get; set; }
        public string Name { get; set; }
    }

ParameterExpression left = (ParameterExpression)operation.Left;这一句出错

[artwl_cn]

有遇到同样问题的朋友们帮忙顶一下啊

[沅江汐水]

修改为 MemberExpression left = (MemberExpression)operation.Left;//这里出错
MemberExpression right = (MemberExpression)operation.Right;

[artwl_cn]

[Quote=引用 2 楼 richet512 的回复:]

修改为 MemberExpression left = (MemberExpression)operation.Left;//这里出错
MemberExpression right = (MemberExpression)operation.Right;
[/Quote]
第一个可以，通过left.member.Name;取到了"ID"值，但第二个不行，取不取值“1”

[子夜__]

[Quote=引用 3 楼 durongjian 的回复:]

引用 2 楼 richet512 的回复:

修改为 MemberExpression left = (MemberExpression)operation.Left;//这里出错
MemberExpression right = (MemberExpression)operation.Right;

第一个可以，通过left.member.Name;取到了"ID"值，但第二个不行，取……
[/Quote]
你说right的值是1吗？

http://blog.zhaojie.me/2010/05/generate-dynamic-method-with-expression-tree-in-dot-net-4.html

[artwl_cn]

[Quote=引用 4 楼 wxr0323 的回复:]

引用 3 楼 durongjian 的回复:

引用 2 楼 richet512 的回复:

修改为 MemberExpression left = (MemberExpression)operation.Left;//这里出错
MemberExpression right = (MemberExpression)operation.Right;

第一个可以，通过left.mem……
[/Quote]
谢谢你的回复，不过现在还看不懂老赵的这篇文章啦

[机器人]

获取1的方法，只能是将MemberExpression弄成一个新的Lambda，然后编译获取值。

Expression.Lambda(right).Compile().DynamicInvoke()

[xiaoqiu1234]

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