如何获取选定值的ID？

Question

I have DropDownList with the following values:

ddl.SelectedValue = { Id = 234, Name = "ABC Name" }

How can I get the value of the Id?

I use WinForms and RadDropDownList

Answer 1

Try this one:

public int GetId(object obj)
{
    var anon = new { Id = 0, Name = string.Empty };
    var obj2 = MakeSameType(obj, anon);
    return obj2.Id;
}

public static T MakeSameType<T>(object obj, T anonymous)
{
    return (T)obj;
}

use it like:

int id = GetId(ddl.SelectedValue);

If it works, it is thanks to how the equivalent anonymous types are "condensed" in single types by the C# compiler.

Note that this solution is as brittle as you can have

If you add/remove/rename a property of the anonymous type, the GetId will break (you'll have to keep the var anon = new {...} perfectly aligned). If you move the method that creates the collection of anonymous types to another assembly it will break too (because only anonymous types inside the same assembly are "unified" by the compiler).

In general you shouldn't have anonymous types that "escape" a method. An anonymous type should remain in the method that it is defined. Assigning it directly as the DataSource of a control is asking for problems.

If you feel lazy and don't want to create a type for a key-value, use the Tuple :

var tuple = Tuple.Create(something, somethingelse, somethingstillelse);
var value1 = tuple.Item1;
var value2 = tuple.Item2;
var value3 = tuple.Item3;

and so on.

Answer 2

As your are using anonymous types, it gets little complicated. But, you can cast SelectedValue to dynamic, and exstract 'Id' from there:

dynamic selectedValue = ddl.SelectedValue;
int id = selectedValue.Id;

But i would recommend to declare your own class or struct for such cases.

Answer 3

I have changed the LINQ query

from:

var query = (from q in tableq where ...
             select new {Id = q.Id, Name = q.Name});

to:

var query = (from q in tableq where ...
             select q);

... and then change it to:

table1.Id = (ddl.SelectedValue as tableq).Id == null ? table1.Id : (ddl.SelectedValue as tableq).Id;