Calling a generic function with a type parameter determined at runtime

Question

I have a question involving calling a class's generic method with a type parameter that is known at runtime.

In specific, the code looks like so:


FieldInfo[] dataFields = this.GetType().GetFields( BindingFlags.Public | BindingFlags.Instance );

// data is just a byte array used internally in DataStream
DataStream ds = new DataStream( data );

foreach ( FieldInfo field in dataFields )
{
    Type fieldType = field.FieldType;

    // I want to call this method and pass in the type parameter specified by the field's type
    object objData = ( object ) ds.Read<fieldType>();
}

The Read() function looks like so:


public T Read() where T : struct

This function's purpose is to return data read from a byte array.

Is there any way to call a generic method at runtime like this?

Lee · Accepted Answer · 2009-09-21T18:30:30.890

12

The easiest way to handle this would be to make a non-generic overload of the Read function with a single Type parameter:

public object Read(Type t)

And then have the generic version call the non-generic version:

public T Read<T>() where T : struct
{
    return (T)Read(typeof(T))
}

edited Sep 21 '09 at 18:30

answered Sep 21 '09 at 18:17

Lee

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Thanks for the reply, I never quite considered such a simple design change. – Ryan Stecker Sep 21 '09 at 18:26
My problem didn't look at all like the OP question, but you demonstrated exactly what I needed to know. Thanks! – KennyZ May 20 '12 at 13:39
This only works if you have control over the method you want to call right? – kipusoep Nov 28 '18 at 08:03

score 7 · Answer 2 · answered Sep 21 '09 at 18:18

7

You'll need to build a methodinfo and invoke the Read method:

MethodInfo method = typeof(DataStream).GetMethod("Read");
MethodInfo generic = method.MakeGenericMethod(fieldType);
object objData = generic.Invoke(ds, null);

answered Sep 21 '09 at 18:18

Reed Copsey

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Thanks again Reed, your help is very much appreciated. – Ryan Stecker Sep 21 '09 at 18:25

score 1 · Answer 3 · answered Sep 21 '09 at 18:20

1

It would probably be better to go Lee's route. Generic's are shorthand at design-time to keep you from having to write common code for many different types of classes. At compile time every call to a generic method or class is basically generated as a completely separate class.

Much simpler to just bass the the type and use reflection, which is what you would have to do anyways.

answered Sep 21 '09 at 18:20

Nick

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True, Lee's method would also be better performance-wise, as the additional reflection to retrieve the MethodInfo would be additional computation that could be avoided with his method. – Ryan Stecker Sep 21 '09 at 18:27

Calling a generic function with a type parameter determined at runtime

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