how to specify the T Generic type for a class at runtime or from parameter [modified]

[supercat9]

Generic reference types are more than syntactic sugar; the compiler only has to produce one JIT-compiled instance of a method that uses a generic reference type, but the method can produce objects which are 'ready to go' in the desired type without the expense of a typecast or other run-time validation. I know of no way such a result could be achieved without generics. There are limits to what generics can do, but they seem to be a very useful feature with significant semantic meaning. Extension methods, by contrast, seem more like syntactic sugar.

[Feras Mazen Taleb]

thanks a lot for your replay and explanation but could you tell me how can I use the second choice I mean how to make the user control accept T as Template something like this :

public class kokoControl : UserControl
{
.....
}

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[Dave Kreskowiak]

What are you ultimately trying to do with this??

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Dave Kreskowiak Microsoft MVP Visual Developer - Visual Basic
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[Feras Mazen Taleb]

ok I'm sorry my replay was not complete . i will tell you the full story :) I made generic class that can make DynamicLinq For any class this class is

public class LinqFilter<T>
{
some of :
public Fun<T,bool> GetFilter()
{
//here i will return
Expression Filter ;
Filter = Expression.And(.....)
..............................
var predicate = Expression.Lambda. .... .
return (Func<T,bool> )predicate.Compile();
}
}

the previous class work well I want to use it inside a user control called FilterControl but I want to make the control also as a Generic Class just to pass the T inside the control

public Class FilterControl<T> : UserControl
{
LinqFilter<T> F;
................
}

but I got an error when tried to do that how can I pass the T from outside the control to the [F] Variable of linqfilter .:confused: thanks

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[Curtis Schlak]

So I fired up Snippet Compiler[^], added System.Core.dll as a reference, and wrote this little snippet of code:

public class Base
{
public Func<t,> GetFilter()
{
return delegate(T t) { return true; };
}
}

public class BaseCotnrol : UserControl
{
Base foo;
}

It compiled just fine. Could you post the compiler error?

"we must lose precision to make significant statements about complex systems." -deKorvin on uncertainty

[Feras Mazen Taleb]

first , thanks a lot for your replay :) I thought that I will not get the answer :^) !! I will try that but could you explain more what should this code do ?

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[Curtis Schlak]

My code doesn't really do anything. &l;smile /> I just wrote some code that looked like your code to make sure that it compiles. It compiled. Unfortunately, that just means that I don't understand the nature of your question. Can you post something more indicative of your plight?

"we must lose precision to make significant statements about complex systems." -deKorvin on uncertainty

[Feras Mazen Taleb]

I will explain I made this class

public class LinqFilter<T>
{
public Fun<T,bool> GetFilter()
{
// in this function I made an Expression Tree after
// that i make lambda expression that return delegate
// this is not important for my problem
// but I said that just to not write empty function .
var predicate = Expression.Lambda. .... .
return (Func<T,bool> )predicate.Compile();
}
}

there is a user control called FilterControl I need to use object of previous class [LinqFilter] inside this control but I want to get The [T] Type from out side the user control the following code make compiler error when i put <T> in User Control definition

public Class FilterControl<T> : UserControl
{
LinqFilter<T> F;
................
}

I hope to not give me joking code again thanks

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[Curtis Schlak]

When you write that you "want to get the [T] Type from out side the user control", what do you mean by that? Do you mean that you want to bind T at runtime rather than at compile time? Something like the following pseudocode?

t <- assign some resolved Type
create an instance of FilterControl dynamically and bind t to T
put the instance of FilterControl`1 on your form

"we must lose precision to make significant statements about complex systems." -deKorvin on uncertainty

[Feras Mazen Taleb]

What I need is : When I put the FilterControl in the window , I want to specify the T Type I mean in Compile Time in this way the control will be able to make filtering on objects of any T class with support from LinqFilter class

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[Curtis Schlak]

Ah ha! Now I understand. The Visual Studio designers do not support controls with unbound generic parameters. You can't create your FilterControl<T> : UserControl and then use the forms designer to drag it onto a panel or form. You might be able to adapt a TypeDescriptor for the user control for your forms, though I've never seen this done. There's an article on Urban Potato that does this for controls with abstract base classes: Using Visual Studio Whidbey to Design Abstract Forms[^].

[Feras Mazen Taleb]

thanks a lot I will read this article ( in sha'a allah) and I hope to find what I want Thanks very match :)

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[Curtis Schlak]

If you find or develop something interesting, then don't forget to come back and post a solution so that we all can learn! :-D

"we must lose precision to make significant statements about complex systems." -deKorvin on uncertainty

[Feras Mazen Taleb]

Okay my friend :)

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