Chad,
> I had the same issue recently, how do I implement a factory
> pattern in C#, having the consumer classes of the factory, the
> factory itself, and the classes it creates all residing in the
> same assembly but not allowing the consumer classes to create any
> of the classes that will be created through the factory. Well
> there is no direct scope level that allows this. The solution
> would be to create internals in a different assembly but that's
> not what I wanted. So this is what I did:
>
> 1) define the common factory interface as public
> 2) define the factory class as public with the factory
> method that returns an interface defined in (1)
> 3) define all classes that implement the interface in (1)
> as private, nested classes inside the factory class
>
<snipped code>
That's a useful technique. Another approach you can use is
to make the factory an base of the individual classes you need
as in the following.
<code>
using System;
namespace ConsoleApplication1
{
public abstract class BaseClass
{
private BaseClass() { }
public static BaseClass Create(string someInfo)
{
switch (someInfo)
{
case "abc":
return new DerivedClass1();
case "xyz":
return new DerivedClass2();
default:
throw new ArgumentException( "I don't know how
to create " +
someInfo );
}
}
public virtual void DoSomething()
{
}
// Nested derived classes
private class DerivedClass1 : BaseClass
{
public override void DoSomething()
{
Console.WriteLine("DerivedClass1 did something");
}
}
private class DerivedClass2 : BaseClass
{
public override void DoSomething()
{
Console.WriteLine("DerivedClass2 did something");
}
}
}
/// <summary>
/// Summary description for Class1.
/// </summary>
class Class1
{
/// <summary>
/// The main entry point for the application.
/// </summary>
[STAThread]
static void Main(string[] args)
{
try
{
BaseClass obj1 = BaseClass.Create("abc");
obj1.DoSomething();
BaseClass obj2 = BaseClass.Create("xyz");
obj2.DoSomething();
BaseClass obj3 = BaseClass.Create("123");
obj3.DoSomething();
}
catch (Exception e)
{
Console.WriteLine ( e.Message );
}
// This gives compiler error
// Cannot create an instance of the abstract class or
interface BaseClass
// BaseClass obj = new BaseClass();
// These give compiler error
// DerivedClass? is inaccessible due to its protection
level
// BaseClass.DerivedClass1 obj = new DerivedClass1();
// BaseClass.DerivedClass2 obj = new DerivedClass2();
// Output is
// DerivedClass1 did something
// DerivedClass2 did something
// I don't know how to create 123
}
}
}
</code>
Charlie Poole
[EMAIL PROTECTED]
www.pooleconsulting.com
www.charliepoole.org
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