Dyanamically referring to an object instance

[RSH]

Hi,

I have a situation where I have multiple objects created from concrete
classes:

// Concrete implementations of the Abstract class ApprovalChain
MarketingApprov alChain MktgAppChain = new MarketingApprov alChain();
AccountingAppro valChain AcctAppChain = new AccountingAppro valChain();

I also have a Department enum
public enum Department
{
Acct,Mktg
}

Armed with that information I need to pass those objects to another class
dynamically. (Im trying to avoid hardcoding the logic is a case conditional:

public class Purchase
{
public Purchase(Approv alChain appChain)
{
...
}

}
back to the original method:
private MarketingApprov alChain MktgAppChain = new MarketingApprov alChain();
private AccountingAppro valChain AcctAppChain = new
AccountingAppro valChain();

public void PurchaseRequisi tion(Department dept)
{
Purchase purchase = new Purchase();<----- is there a way here to use the
string value of the enum to dynamically make reference to the appropriate
ApprovalChain to pass to the Purchase Class Constructor?
}

PsuedoCode: Purchase purchase = new Purchase(dept.T oString() +
"ApprovalChain" );

Thanks alot!

Ron

[cfps.Christian]

Took me a minute to figure out what you wanted to do.

You're looking for the Activator.Creat eInstance method.

What I would do is:

ApprovalChain appChain;
appChain = (ApprovalChain) Activator.Creat eInstance([fully qualified
name] + dept.ToString() + "ApprovalChain" )
Purchase purchase = new Purchase(appCha in);

I'm not really up on my CreateInstance code but thats definitely what
you're looking for. The string that you pass in has to be the fully
qualified name of the type you are defining.

[RSH]

Almost....

The only problem is that the objects already have been created and they
contain state that needs to be persisted which is handled by the class that
contains the method Im illustrating here. I need to dynamically construct a
reference to the appropriate object (based on the deparment enum passed to
the method) and then pass the "live" object to the Purchase object. Right
now I am using a case conditionional:

public void PurchaseRequest (int id, double amount, string description,
eGroup group)

{

Purchase purchase;

switch (group)

{

case eGroup.Marketin g:

this.

purchase = new Purchase(id, amount, description, group,
marketingapprov alchain, marketingbudget );

break;

case eGroup.Accounti ng:

purchase = new Purchase(id, amount, description, group,
accountingappro valchain, accountingbudge t);

break;

}

}

}

But since I dont know the number of departments the system will ultimately
contain, I dont want to hardcode the references in a conditional.

Thanks!

Ron

"cfps.Christian " <ge*******@otc. eduwrote in message
news:f6******** *************** ***********@e1g 2000hsh.googleg roups.com...

Took me a minute to figure out what you wanted to do.

You're looking for the Activator.Creat eInstance method.

What I would do is:

ApprovalChain appChain;
appChain = (ApprovalChain) Activator.Creat eInstance([fully qualified
name] + dept.ToString() + "ApprovalChain" )
Purchase purchase = new Purchase(appCha in);

I'm not really up on my CreateInstance code but thats definitely what
you're looking for. The string that you pass in has to be the fully
qualified name of the type you are defining.

[Mattias Sjögren]

>PsuedoCode: Purchase purchase = new Purchase(dept.T oString() +
"ApprovalChain ");

How about a simple mapping table?

Dictionary<Depa rtment, ApprovalChainma p = new Dictionary<Depa rtment,
ApprovalChain>( );
map.Add(Departm ent.Acct, AcctAppChain);
map.Add(Departm ent.Mktg, MktgAppChain);

....

Purchase purchase = new Purchase(map[dept]);
Mattias

--
Mattias Sjögren [C# MVP] mattias @ mvps.org
http://www.msjogren.net/dotnet/ | http://www.dotnetinterop.com
Please reply only to the newsgroup.

[Peter Duniho]

On 2007-11-30 14:03:41 -0800, "RSH" <wa************ *@yahoo.comsaid :

[...]
But since I dont know the number of departments the system will ultimately
contain, I dont want to hardcode the references in a conditional.

It's difficult for me to be sure I completely understand the question.
I don't find the description very organized. But, that said...

It seems to me that what you've got are already-existing instances of
ApprovalChain-derived classes that are somehow related to your
instantiation of the Purchase class. It appears you may also have a
class named "Budget" that also has derived versions you're using.

Given that, you may want to consider just storing those instances in a
Dictionary<T>, so that you can easily look them up according to their
enum value. For example:

enum Department
{
Acct, Mktg
}

struct DepartmentObjec ts
{
public readonly ApprovalChain ApprovalChain;
public readonly Budget Budget;

public DepartmentObjec ts(ApprovalChai n ApprovalChain, Budget Budget)
{
this.ApprovalCh ain = ApprovalChain;
this.Budget = Budget;
}
}

static Dictionary<Depa rtment, DepartmentObjec tsdictDepartmen ts;

// run once somewhere (e.g. static constructor for whatever class
// contains the "dictDepartment s" object)
foreach (Department dept in Department.GetV alues())
{
switch (dept)
{
case Acct:
dictDepartments .Add(dept, new DepartmentObjec ts(new
AccountingAppro valChain(), new AccountingBudge t()));
break;
case Mktg:
dictDepartments .Add(dept, new DepartmentObjec ts(new
MarketingApprov alChain(), new MarketingBudget ()));
break;
}
}
// then wherever you need to match the enum to an instance, something
// like this:

Department dept = // initialized however...;

ApprovalChain approval = dictDepartments[dept].ApprovalChain;

// Or you could do this:
DepartmentObjec t do = dictDepartments[dept];
Purchase purchase = new Purchase(id, amount, description, dept,
do.ApprovalChai n, do.Budget);

etc.

Note that at some point you do need to hardcode the relationship
between your enum and the class each value represents. Depending on
the actual names you've used for things it certainly is possible to use
reflection to even automate that, but it seems to me it wouldn't really
buy you much. It's not like you can just go adding new ApprovalChain
and Budget objects without visiting the code that uses those objects
and verifying you've done everything right anyway (or at least you
ought to be).

Pete

[RSH]

Peter,

Thanks! Good stuff...that worked perfectly!

I agree that at some point I need to hardcode the names, but I wanted to do
it in one place only. Your solution will provide me that.

thanks!
Ron
"Peter Duniho" <Np*********@Nn OwSlPiAnMk.comw rote in message
news:2007113014 274150878-NpOeStPeAdM@NnO wSlPiAnMkcom...

On 2007-11-30 14:03:41 -0800, "RSH" <wa************ *@yahoo.comsaid :

>[...]
But since I dont know the number of departments the system will
ultimately
contain, I dont want to hardcode the references in a conditional.

It's difficult for me to be sure I completely understand the question. I
don't find the description very organized. But, that said...

It seems to me that what you've got are already-existing instances of
ApprovalChain-derived classes that are somehow related to your
instantiation of the Purchase class. It appears you may also have a class
named "Budget" that also has derived versions you're using.

Given that, you may want to consider just storing those instances in a
Dictionary<T>, so that you can easily look them up according to their enum
value. For example:

enum Department
{
Acct, Mktg
}

struct DepartmentObjec ts
{
public readonly ApprovalChain ApprovalChain;
public readonly Budget Budget;

public DepartmentObjec ts(ApprovalChai n ApprovalChain, Budget
Budget)
{
this.ApprovalCh ain = ApprovalChain;
this.Budget = Budget;
}
}

static Dictionary<Depa rtment, DepartmentObjec tsdictDepartmen ts;

// run once somewhere (e.g. static constructor for whatever class
// contains the "dictDepartment s" object)
foreach (Department dept in Department.GetV alues())
{
switch (dept)
{
case Acct:
dictDepartments .Add(dept, new DepartmentObjec ts(new
AccountingAppro valChain(), new AccountingBudge t()));
break;
case Mktg:
dictDepartments .Add(dept, new DepartmentObjec ts(new
MarketingApprov alChain(), new MarketingBudget ()));
break;
}
}
// then wherever you need to match the enum to an instance, something
// like this:

Department dept = // initialized however...;

ApprovalChain approval = dictDepartments[dept].ApprovalChain;

// Or you could do this:
DepartmentObjec t do = dictDepartments[dept];
Purchase purchase = new Purchase(id, amount, description, dept,
do.ApprovalChai n, do.Budget);

etc.

Note that at some point you do need to hardcode the relationship between
your enum and the class each value represents. Depending on the actual
names you've used for things it certainly is possible to use reflection to
even automate that, but it seems to me it wouldn't really buy you much.
It's not like you can just go adding new ApprovalChain and Budget objects
without visiting the code that uses those objects and verifying you've
done everything right anyway (or at least you ought to be).

Pete