如何在C＃中使用变量的值作为键来声明匿名类型？

Question

Is there anyway to succeed this sample?

string[] columns = ["a","b","c","d"];
var headers = from column in columns
select new
{
  title = column,
  filter = new  { column = "select" },
  show = true
}; 

After debug this code block, I see header.filter.column property. How can I see header.filter.a ?

Answer 1

This is not possible, since anynonymous types are anonymous , but they still exist at compile time . So you can not create an anonymous class with runtime member names. What you are actually doing is to set a property named column with the value "select" .

What you can do though is to create a dictionary from your result and access the data with the dictionary:

var headerFilterDictionary = headers.ToDictionary(item => item.title, item => item.filter.column);

var columnFilterValue = headerFilterDictionary["a"];

Answer 2

This probably isn't what you really want to do (at all), but you can make the syntax (mostly) work by using dynamic :

    static void Main(string[] args)
    {
        string[] columns = { "a", "b", "c", "d" };
        var headers = from column in columns

                      let c_a = (dynamic)(column == "a" ? new { a = column } : null)
                      let c_b = (dynamic)(column == "b" ? new { b = column } : null)
                      let c_c = (dynamic)(column == "c" ? new { c = column } : null)
                      let c_d = (dynamic)(column == "d" ? new { d = column } : null)

                      select new
                      {
                          title = column,
                          filter = c_a ?? c_b ?? c_c ?? c_d,
                          show = true
                      };

        var filter_0 = headers.ElementAt(0).filter.a;
        var filter_1 = headers.ElementAt(1).filter.b;
        var filter_2 = headers.ElementAt(2).filter.c;
        var filter_3 = headers.ElementAt(3).filter.d;
    }

Obviously, this doesn't scale very well; and since it's dynamic, you don't get IntelliSense on filter .

This is probably best considered for entertainment purposes only.