lambda表达式和铸造

Question

        var objectType = cmbObjectType.SelectedItem as Type;
        var property = cmbProperty.SelectedItem as PropertyInfo;
        var oper = cmbOperator.SelectedValue;

        var item = Expression.Parameter(objectType);
        var prop = Expression.Property(item, property);

        BinaryExpression condition=null;

        var filtered = tlproject.TlObjects.Where(obj => obj.GetType().Equals(objectType)).AsQueryable();

...
        var lambda = Expression.Lambda<Func<TLObject, bool>>(condition, item);                    
        var results = filtered.Where(lambda);

这不起作用，因为对象从TLObject继承，给出了像

这样的错误

  

附加信息：ParameterExpression类型   'TLObjects.Pipe'不能用于类型的委托参数   'TLObjects.Base.TLObject'

我该如何解决这个问题？ 的更新 这似乎有效

  var item = Expression.Parameter(typeof(TLObject));
    var itemConverted=Expression.Convert(item, objectType);
    var prop = Expression.Property(itemConverted, property);