🚀 go-pugleaf

"Shawn Oster" <soster@colorflex.com> a �crit dans le message de news: 
458c5f4b@newsgroups.borland.com...

| I'm trying to port a factory I use in Delphi to C# and have hit a snag. 
In
| Delphi I usually make light-weight factories like this:
|
| TGizmo = class(TObject)
| // stuff here
| end;
|
| TGizmoClass = class of TGizmo;
|
| TGizmoFactory = class(TObject)
| private
|   FHashedListOfGizmoClasses: TClassHashList;
| public
|   procedure RegisterClass(const ClassKey: string; ClassType: TGizmoClass);
|   function CreateObject(const ClassKey: string): TGizmo;
| end;
|
| As you can see I pass in a key and a class type, then in CreateObject I
| simply look up the key in the hash, call TGizmoClass.Create and *bam* 
there
| is my new object.
|
| My question is: How can I create a type-safe class type to pass into my
| factory?  All the examples I see require creating a concrete factory for
| every concrete class but that seems like a waste.  I'm sure I'm just
| overlooking something super simple.

Are you using .NET 2.0 ?

If so, use the Dictionary<K,V> instead of your HashList, but a factory 
method can be really simple :

public static class GizmoFactory
{
  public static Gizmo CreateObject<T>() where T : Gizmo, new()
  {
    return new T();
  }
}

This is then used like this :

public class Gizmo
{
}

public class Derived : Gizmo
{
}

void Test()
{
  Gizmo g = GizmoFactory.CreateObject<Derived>();
  ...
}

But then I guess you might as well use the straigtforward constructor call 
anyway :-(

If you want to use a string key for a hash list that has a type value, then 
this becomes a bit more difficult and you will have to lose type safety in 
order to use Activator.CreateInstance() instead to create your instances.

I have created a C# metaclass but it is not typesafe at compile time, if you 
use System.Type as the value part of a Dictionary key, then you can only 
check for type at runtime.

Joanna

-- 
Joanna Carter [TeamB]
Consultant Software Engineer 

On Fri, 22 Dec 2006 15:42:34 -0700, Shawn Oster wrote:

> My question is: How can I create a type-safe class type to pass into my 
> factory?  All the examples I see require creating a concrete factory for 
> every concrete class but that seems like a waste.  I'm sure I'm just 
> overlooking something super simple.

Generally you use the System.Type object.

System.Type t = typeof(Gizmo);
or
System.Type t = GizmoInstance.GetType();

then
  Gizmo g = (Gizmo)Activator.CreateInstance(t, constructor_params);

-- 
Marc Rohloff [TeamB]
marc rohloff -at- myrealbox -dot- com