Re: Dynamic Types in Generics? - C# Discussion Boards

Re: System.NullReferenceException was unhandled by user code, Object reference not set to an instance of an object.

Vimalsoft(Pty) Ltd15-Jul-09 20:31

15-Jul-09 20:31

You are Doing String Concatination. The only thing that might cause this error is the "cmd" if you dont hava a statement above this code that says

SqlCommand cmd = new  SqlCommand();

then that is a problem, because the incorect string concatination will not give this error descritption

Vuyiswa Maseko,

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C#/VB.NET/ASP.NET/SQL7/2000/2005/2008
http://www.vuyiswamaseko.somee.com
http://www.vuyiswamaseko.tiyaneProperties.co.za
vuyiswa@its.co.za
http://www.itsabacus.co.za/itsabacus/

Which C# Book?

321Markus12315-Jul-09 16:07

321Markus123

15-Jul-09 16:07

Hi,

I'm a C++ programmer looking to learn C#, I have no experience with .NET, I bought "Essential C# 2.0" a few years back but never got a chance to read it.

Could somebody recommend a good C# book, preferably using the .NET 3.5 framework - these three all seem to be well rated so I don't know which (if any) to choose:

Apress - Pro C# 2008 and the .NET 3.5 Platform, Fourth Edition
Wrox - Professional C# 2008
C# 3.0 in a Nutshell: A Desktop Quick Reference

Thanks in advance for any suggestions.

Re: Which C# Book?

PIEBALDconsult15-Jul-09 17:09

PIEBALDconsult

15-Jul-09 17:09

321Markus123 wrote:
Wrox - Professional C# 2008

-- I have an older version (from 2003) that I had to buy for a class way back then, it seems pretty good.

Dynamic Types in Generics?

NandoMan15-Jul-09 11:49

NandoMan

15-Jul-09 11:49

Hello people,

Is it posible to declare the type of a generic at runtime?

I mean, you normaly would have to do something like this:
GenericMethod<Type>();

And I want to do something like this:
GenericMethod<(expression that evaluates to a type)>();

I have tried a few things but nothing seems to work.
MSDN's C# Programming Guide states that:

"client code must declare and instantiate a constructed type by specifying a type argument inside the angle brackets. The type argument for this particular class can be any type recognized by the compiler."

Thanks!

Re: Dynamic Types in Generics?

Pete O'Hanlon15-Jul-09 12:05

Pete O'Hanlon

15-Jul-09 12:05

You could always use a Func here. For instance:

GenericMethod<Func<T, TResult>>();

"WPF has many lovers. It's a veritable porn star!" - Josh Smith

As Braveheart once said, "You can take our freedom but you'll never take our Hobnobs!" - Martin Hughes.

My blog | My articles | MoXAML PowerToys | Onyx

Re: Dynamic Types in Generics?

NandoMan15-Jul-09 12:14

NandoMan

15-Jul-09 12:14

Thanks Pete,

And what exactly would this Func be or do?

Thanks again!

Re: Dynamic Types in Generics?

Pete O'Hanlon15-Jul-09 12:17

Pete O'Hanlon

15-Jul-09 12:17

This[^] article should help. This type of functionality is the mojo behind Linq.

"WPF has many lovers. It's a veritable porn star!" - Josh Smith

As Braveheart once said, "You can take our freedom but you'll never take our Hobnobs!" - Martin Hughes.

My blog | My articles | MoXAML PowerToys | Onyx

Re: Dynamic Types in Generics?

DaveyM6915-Jul-09 13:30

DaveyM69

15-Jul-09 13:30

Good link Pete, very concise. Big Grin | :-D

Dave
BTW, in software, hope and pray is not a viable strategy. (Luc Pattyn)
Visual Basic is not used by normal people so we're not covering it here. (Uncyclopedia)
Why are you using VB6? Do you hate yourself? (Christian Graus)

Re: Dynamic Types in Generics?

NandoMan16-Jul-09 6:34

NandoMan

16-Jul-09 6:34

Thanks Pete, I read your link and it seems this particular feature it's not for C# 2.0, which is preciselly the version i'm working Frown | :(

Re: Dynamic Types in Generics?

harold aptroot15-Jul-09 13:34

harold aptroot

15-Jul-09 13:34

What kind of expression that evaluates to a type would you have there? Something with reflection? You could probably use reflection to invoke the method with an expression of the type Type, but I'm not actually sure. Reflection can do a lot though, so why not..
edit: If all else fails, there is still the possibility to compile and run a piece of code that has been generated at runtime. But I wouldn't use that except in emergencies. It's not exactly fast, or a clean design.

Re: Dynamic Types in Generics?

0x3c015-Jul-09 21:12

0x3c0

15-Jul-09 21:12

A method which may prove useful is Type.MakeGenericType[^]. I don't fully understand it, but it seems to be a step in the right direction - getting the type of a generic type (without the type specifiers), then calling MakeGenericType on the result to get a dynamically set Type

Between the idea
And the reality
Between the motion
And the act
Falls the Shadow

Re: Dynamic Types in Generics?

NandoMan16-Jul-09 9:19

NandoMan

16-Jul-09 9:19

Man thanks a lot, it did worked:

Type cons = typeof(List<>).MakeGenericType(Tipo);

object _list = cons.Assembly.CreateInstance(cons.FullName);

+1 for you!

Re: Dynamic Types in Generics?

Eslam Afifi16-Jul-09 7:13

Eslam Afifi

16-Jul-09 7:13

This code creates a generic type and instatiate an object of that type in runtime using MakeGenericType as Computafreak mentioned. I was going to post it last night but I forgot and fell asleep. But now I know you want it in .net 2.0 I have to remove var and new[]

static void Main(string[] args)
{
    Type t = typeof(List<> );
    Type gt = t.MakeGenericType(GetTypes());
    object gtObj = Activator.CreateInstance(gt);
}

private static Type[] GetTypes()
{
    return new Type[] { typeof(int) };
}

But gtObj is returned as an object (but it is a List<int>). The problem is that you will probably have to use reflection.

Eslam Afifi

Re: Dynamic Types in Generics?

NandoMan16-Jul-09 9:18

NandoMan

16-Jul-09 9:18

Thanks a lot!

Re: Dynamic Types in Generics?

Eslam Afifi16-Jul-09 10:12

Eslam Afifi

16-Jul-09 10:12

You're welcome. I read your other post[^] and you don't have to use the FullName of the Type, you can just pass the Type directly which is faster IMHO.

Eslam Afifi

Re: Dynamic Types in Generics?

NandoMan16-Jul-09 12:02

NandoMan

16-Jul-09 12:02

Yes indeed! I have corrected my code to use the Activator.

Thanks again!

computer share rights

caiena15-Jul-09 6:54

caiena

15-Jul-09 6:54

i am looking for a way to list all the share on a given computer and also list all groups on users who have access and what access they have

Re: computer share rights

dan!sh 15-Jul-09 7:18

dan!sh

15-Jul-09 7:18

Here[^] you go. There is an article right here[^] at CP.

For the other part, I guess this[^] would help.

Re: computer share rights

caiena15-Jul-09 8:44

caiena

15-Jul-09 8:44

what i am really looking to do is check the total right a users has to a share do i have to find out all the groups they are in and get all the rights for each group and calulate it my self or is there and easier way?

SQL Table

kibromg15-Jul-09 6:12

kibromg

15-Jul-09 6:12