測試程式碼

using NUnit.Framework;

namespace LocalVarExpression
{
    [TestFixture]
    public class LocalExpressionTest
    {
        private int _intField = 2;
        public int IntProp { get; set; }
        [SetUp]
        public void SetUp()
        {
            IntProp = 4;
        }
        [Test]
        public
 
 void TestGetLocalValue()
        {
            var localVar = 7;

            var t1 = LocalExpression.GetValue(() => 1);
            var t2 = LocalExpression.GetValue(() => _intField);
            var t3 = LocalExpression.GetValue(() => IntProp);
            var t4 = LocalExpression.GetValue(() => localVar);

            Assert.AreEqual(1
 
, 1);
        }
    }
}

核心程式碼

using System;
using System.Linq;
using System.Linq.Expressions;
using System.Reflection;

namespace LocalVarExpression
{
    /// <summary>
    /// 支援本地變數的Expression
    /// </summary>
    public class LocalExpression
    {
        public static object GetValue<T>(Expression<Func<T>> func)
        {
            object
 
 value=new object();
            var body = func.Body;

            if (body.NodeType == ExpressionType.Constant)
            {
                value = ((ConstantExpression)body).Value;
            }
            else
            {
                var memberExpression = (MemberExpression)body;

                var @object =
                  ((ConstantExpression)(memberExpression.Expression)).Value; //這個是重點

                if (memberExpression.Member.MemberType == MemberTypes.Field)
                {
                    value = ((FieldInfo)memberExpression.Member).GetValue(@object);
                }
                else if (memberExpression.Member.MemberType == MemberTypes.Property)
                {
                    value = ((PropertyInfo)memberExpression.Member).GetValue(@object);
                }
            }
            return value;
        }
    }
}