MemberExpression：从范围”引用的InvalidOperationExpression变量\'x\'，但未定义
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我正在使用System.Linq.Expressions
我试图构建一个包含MemberExpression的简单LambdaExpression。如果我使用System.Linq.Expressions API（例如MakeMemberAccess）显式创建MemberExpression，则会收到错误“从范围\'\'引用的InvalidOperationExpression变量\'x \'，但未定义\“在LambdaExpression上调用Compile（）。
例如，这是我的代码
Expression<Func<Customer, string>> expression1, expression2, expression3;
Func<Customer, string> fn;
expression1 = (x) => x.Title;
fn = expression1.Compile();//works
fn(c);
MemberExpression m;
m = Expression.MakeMemberAccess(
Expression.Parameter(typeof(Customer), \"x\"), typeof(Customer).GetProperty(\"Title\"));
expression2 = Expression.Lambda<Func<Customer, string>>(m,
Expression.Parameter(typeof(Customer), \"x\"));
m = Expression.Property(Expression.Parameter(typeof(Customer),\"x\"), \"Title\");
expression3 = Expression.Lambda<Func<Customer, string>>(m,
Expression.Parameter(typeof(Customer), \"x\"));
fn = expression3.Compile();//InvalidOperationExpression variable \'x\' referenced from scope \'\', but it is not defined
fn = expression2.Compile();//InvalidOperationExpression variable \'x\' referenced from scope \'\', but it is not defined
没有找到相关结果
已邀请:
1 个回复
究补闯
ParameterExpression p = Expression.Parameter(typeof(Customer), \"x\"); MemberExpression m = Expression.MakeMemberAccess(p, typeof(Customer).GetProperty(\"Title\")); expression2 = Expression.Lambda<Func<Customer, string>>(m, p); m = Expression.Property(p, \"Title\"); expression3 = Expression.Lambda<Func<Customer, string>>(m, p); fn = expression3.Compile(); fn = expression2.Compile();