How to specify the type of an anonymous type while using a generic type

Question

The title is pretty confusing. I will try to explain with an example. Consider the code below:

String[] str={"Apple","Banana","Cherry","Orange"};
var anoCollection=from e in str select new
                                         {
                                          ch=e[0],
                                          length=e.Length
                                         }
dataGridView.DataSource=anoCollection.ToList(); //TypeInitializationException

I feel that I need to mention the type in above case for the ToList<T>() method. But how can I mention an anonymous type here?

@TimSchmelter actually, in many cases the `.ToList()` version would be preferable, especially in winforms - it wants an `IList`, and a *sequence* will not work — Marc Gravell, Jan 03 '13 at 13:24
TypeInitializationException comes with an InnerException; what does *that* say? That tells you what the actual problem was. — Marc Gravell, Jan 03 '13 at 13:40
@MichaelPerrenoud that is certainly a related topic, but I don't think that addresses the question here — Marc Gravell, Jan 03 '13 at 13:42

score 3 · Accepted Answer · answered Jan 03 '13 at 13:23

It is never possible to mention an anonymous type directly, but you should not need to. Generic type inference means that you don't need to specify the <T> in .ToList<T>() - the compiler will automatically inject the invented type.

There are only a few ways to refer to an anonymous type:

via someObj.GetType(), where someObj is an instance of an anonymous type
via generics, as a T, by calling a generic method via generic type inference (as in ToList())
various other usages of reflection, pulling in the T via GetGenericTypeParameters()

score 0 · Answer 2 · answered Jan 03 '13 at 13:32

0

This may be not what you are asking for, but if you later want to use the DataBoundItem for a row, you can do it this way:

var item = TypeExtensions.CastByPrototype(row.DataBoundItem, new { ch = 'a', length = 0});
//you can use item.ch and item.length here
Trace.WriteLine(item.ch);

with the support of this method:

public static class TypeExtensions
{
    public static T CastByPrototype<T>(object obj, T prototype)
    {
        return (T)obj;
    }
}

answered Jan 03 '13 at 13:32

deerchao

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You can make this a bit more readable by making it an extension method and naming it `CastToTypeOf`. So all this reads: `row.DataBoundItem.CastToTypeOf(new { ch = 'a', length = 0 })`. – nawfal Jun 28 '14 at 16:30

How to specify the type of an anonymous type while using a generic type

2 Answers2