使用表達式樹導航並返回擁有屬性的對象

Question

給定一個指向對象圖中屬性的表達式，我想檢索擁有該圖的屬性的實例。我一直在掙扎。當前的代碼只是給了我System.InvalidOperationException：LAMBDA參數不在範圍內

[Test] 
    public void TestExpression() 
    { 
     var person = new Person {Address = {Street = "Bank Street"}, Name = "Joe"}; 

     Expression<Func<Person, object>> exp = p => p.Address.Street; 
     Assert.AreEqual("Bank Street", exp.Compile().Invoke(person)); 

     var owner = GetPropertyOwner(person, exp); 
     Assert.AreEqual(owner, person.Address); 
    } 

    private object GetPropertyOwner<T>(T root, Expression<Func<T, object>> exp) 
    { 
     if (exp.Body is MemberExpression) 
     { 
      var member = exp.Body as MemberExpression; 
      if (member.Expression is MemberExpression) 
      { 
       var parentMember = member.Expression as MemberExpression; 
       //parent member will be {p.Address} 
       //Now I'm trying to reconstruct an expression that I can combile 
       var parameterExpression = System.Linq.Expressions.Expression.Parameter(typeof(T), "p"); 
       var lambdaExpression = System.Linq.Expressions.Expression.Lambda(parentMember, parameterExpression); 
       //Next Linethrows System.InvalidOperationException : Lambda Parameter not in scope 
       var found = lambdaExpression.Compile().DynamicInvoke(person); 
       return found; 
      } 
     } 

     return new object(); 
    } 

Answer 1

ParameterExpression對象是通過引用平等相比，叫不上名字，所以「P」參數lambdaExpression需要的是不一樣的一個用於parentMember。當您構建新的lambda時，您將需要使用相同的ParameterExpression實例。試試：

var parameterExpression = exp.Parameters[0];