.NET (Core and Framework)

25-Jun-07 2:38

I have a slightly different problem, I have a generic function that handles populating all the properties of a class and all it's inhreited class objecs. Such as this:

public static List<iperson> TGeneratePersonList(IDataReader oDR, ePersonType PersonType)
{
ArrayList oCols = Field.GetColumnNames(oDR);
oCols = Utilities.Field.GetColumnNames(oDR);
iPerson oP = null;
List<iperson> oPList = new List<iperson>();
while (oDR.Read())
{
switch (PersonType)
{
case ePersonType.Basic:
oP = new Person();
break;
case ePersonType.Contract_Person:
oP = new Contract_Person();
((Contract_Person)oP).Contract_Person_ID = Field.GetInt(oDR, "Contact_ID");
break;
case ePersonType.Vendor_Person:
oP = new Vendor_Person();
break;
}
oPList.add(oP);
}
return oPList;
}

THe problem is when I try to assign this result to a property of an object deined as :
public List<vendor_person> Personnel_List
{
get
{
if (this._Personnel_List == null)
this._Personnel_List = new List<vendor_person>();
return this._Personnel_List;
}
set
{
this._Personnel_List = value;
}

}

I get this at compile time:
Error 4 Cannot implicitly convert type 'System.Collections.Generic.List<projectcentral.contacts.iperson>' to 'System.Collections.Generic.List<projectcentral.contacts.vendor_person>' C:\Projects\ProjectCentral\ProjectCentral.Vendors\GenericVendor.cs 281 39 ProjectCentral.Vendors

Any ideas? It's rather urgent since I've been fighting with this for days and my job is on the line.

THanls;

Andy L 225-Jun-07 7:10

25-Jun-07 7:10

You need to pre-define the type for the generic List class to the type of the object that will be populating it i.e. iPerson so assuming classes Person, Contract_Person and Vendor_Person are all derived from iPerson your code needs to change to the following:

public static List<iPerson> TGeneratePersonList(IDataReader oDR, ePersonType PersonType)
{
...

iPerson oP = null;
List<iPerson> oPList = new List<iPerson>();

...
}

and your property to:

public List<iPerson> Personnel_List
{
...
}

and the field _Personnel_List to:

private List<iPerson> _Personnel_List;

Incidentally, the TGeneratePersonList() is not a generic method - it is an ordinary method that returns a generic List of type iPerson.

This is a generic method:
public void GenericMethod<T>() // Where type T is defined when the method is called
{
// Do something with T in here
}

example calls

GenericMethod<int>();
GenericMethod<string>();
GenericMethod<MyClass>();

Santiago Perez25-Jun-07 8:32

25-Jun-07 8:32

With this scenario I would have to cast property Personnel_List everytime I need to get a property value from one of the derived objects. Doesn't this defeat the purpose of Generics? I guess I'm trying find the most efficient and scalable way to do this.

I tried a different approach as follows. I can't seem to find a way to have the Base class properties populated without having to re-wite the property assignment code in the derived classes.
Anyone encountered this before?

using System;
using System.Collections.Generic;
using System.Text;

namespace ConsoleApplication1
{
class Program
{
static void Main(string[] args)
{
B objB = new B();
List oBList = new List();
objB.GenerateList(ref oBList);

}
}

public interface iClass
{
string Full_Name
{
get;
set;
}

string Short_Name
{
get;
set;
}
}

public class A : iClass
{
private string _PhoneA = "";
private string _Full_Name = "";
private string _Short_Name = "";

public string PhoneA
{
get { return _PhoneA; }
set { _PhoneA = value; }
}

public string Full_Name
{
get { return _Full_Name; }
set { _Full_Name = value; }
}
public string Short_Name
{
get { return _Short_Name; }
set { _Short_Name = value; }
}

public virtual void GenerateList(ref List List)
{
A objA = new A();
objA.Full_Name = "Tom";
List.Add(objA);

objA = new A();
objA.Full_Name = "Bob";
List.Add(objA);

objA = new A();
objA.Full_Name = "Gerry";
List.Add(objA);

}

}

class B : A, iClass
{
private string _SSN = "";

public string SSN
{
get { return _SSN; }
set { _SSN = value; }
}

public new void GenerateList(ref List List)
{
base.GenerateList(ref List);

foreach (B oB in List)
{
oB.SSN = "123";
}

}
}
}

Andy L 226-Jun-07 0:16

26-Jun-07 0:16

Maybe I am missing the point somewhere but I cannot see why you need to use generics to do this.

In my previous example by placing all the initialisation properties into iPerson for example would enable you to initialise all classes derived from iPerson i.e.

// Interface that defines properties and methods to be called during initilaisation
public interface I
{
string Prop1 { get; set; }
int Prop2 { get; set; }
void Initialise(params object[] arrParams);
}

// Classes to be initialised
class A: I
{
private string _prop1 = null;
private int _prop2;

// Interface implementations
string I.Prop1
{
get { return _prop1; }
set { _prop1 = value; }
}

int I.Prop2
{
get { return _prop2; }
set { _prop2 = value; }
}

void I.Initialise(params object[] arrParams)
{
// Do some initialisation on params
Initialise(arrParams);
}

// Option for in class initialisation - could use virtual.
protected abstract void Initialise(params object[] arrParams);
}

class B: A
{
protected override void Initialise(params object[] arrParams)
{
}
}

class C: B
{
private string Prop3 = null;

protected override void Initialise(params object[] arrParams)
{
}
}

Now using interface I to initialise instances of A, B or C as follows:
//Create list
List<I> items = new List<I>();

// This could equally be:
// ArrayList items = new ArrayList();
....
if (ClassType == eType.A)
{
items.Add(new A());
}
else if (ClassType == eType.B)
{
items.Add(new B());
}
else if (ClassType == eType.C)
{
items.Add(new C());
}

// Initialisation can be performed on object instances of type A, B and C this way using interface I no casting required.
foreach (I item in items)
{
// Initialise object properties
item.Prop1 = source.P1;
item.Prop2 = source.P2;

//Or even call an initialise method on the object itself.
item.Initialise(source.P1, source.P2, "P3");
}

This example relies on a single interface structure defined at compile time, this is also a requirement that applies to generics - if what you are looking for is to try and initialise objects by examining their structures at run-time then this falls into the realms of Reflection - and only do this if for some reason you really need to.

If you are requiring to initialise properties that apply to the derived classes (i.e class C)
you could used the Initialise() method shown but you would have to either apply strict parameter ordering or employ a mechanism for identifying which parameter goes to which property.

Santiago Perez26-Jun-07 16:41

26-Jun-07 16:41

Sorry man, you went out to left field and away from the topic at hand. Thanks for your help anyway.

Santiago Perez26-Jun-07 18:28

26-Jun-07 18:28

Ok, I apologize again. Just having a frustrating day. I think I follow what you were trying to explain. I've also watched the webcast from Juval Lowy. What I was trying to explain in my previous post is that I got my function (not a method) to return a generic list of an interface that all my classes implement. What I don't quite understand is how I use this list in the referencing call if I'm expecting a List of of a specific type that implements that interface. Basically it looks to me like I have to iterate throuh the list and cast each object to my desired type in order to get the intelisense etc. Are you saying that I should have my function call look like this based on my last example? If so this won't compile because I get the following error on each result.Add()

Error 1 The best overloaded method match for 'System.Collections.Generic.List<t>.Add(T)' has some invalid arguments C:\Projects\ConsoleApplication1\ConsoleApplication1\Program.cs 95 17 ConsoleApplication1
Error 2 Argument '1': cannot convert from 'ConsoleApplication1.A' to 'T' C:\Projects\ConsoleApplication1\ConsoleApplication1\Program.cs 95 28 ConsoleApplication1

public static List<t> GetList<t>() where T : A,iClass
{
List<t> result = new List<t>();
iClass oC = null;
if (typeof(T) == typeof(A))
{
oC = new A();
((A)oC).Full_Name = "A_Tom";
result.Add((A)oC);

oC = new A();
((A)oC).Full_Name = "A_Bill";
result.Add((A)oC);

oC = new A();
((A)oC).Full_Name = "A_Jack";
result.Add((A)oC);

}
else if (typeof(T) == typeof(B))
{
oC = new B();
((B)oC).Full_Name = "b_Tom";
result.Add((B)oC);

oC = new B();
((B)oC).Full_Name = "B_Bill";
result.Add((B)oC);

oC = new B();
((B)oC).Full_Name = "B_Jack";
result.Add((B)oC);
}
return result;
}

Santiago Perez26-Jun-07 20:19

26-Jun-07 20:19

I got it , I got it, I got it!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

f
public static List<t> GetList<t>() where T :B, iClass, new()
{
T obj = new T();
List<t> result = new List<t>();

if (typeof(T) == typeof(A))
{

((A)obj).PhoneA = "444-4444";
result.Add(obj);
}
else if (typeof(T) == typeof(B))
{
((B)obj).SSN = "123-12-1111";
result.Add(obj);
}

return result;
}

Andy L 226-Jun-07 22:37

26-Jun-07 22:37

You are still having to cast classes A and B though???? Confused | :confused:

Santiago Perez27-Jun-07 5:05

27-Jun-07 5:05

Here's my thing that I don't understand about what you presented earlier, you say to use the Initialise method of the Interface on each individual Derrived class to initilise that instance. My problem with this sample is that you're using an array of type object[] which in itself will do implicit cast on each item thus degrading performance. Secondly you're example of

//Or even call an initialise method on the object itself.
item.Initialise(source.P1, source.P2, "P3");
}

tells me that you will need to write an Initialisation override on each generation of the object, in this case to be able to handle "P3". I guess if it's a virtual you could call base.Initialise and pass it the same params. WOuld that be way to go?

Santiago Perez27-Jun-07 5:29

27-Jun-07 5:29

I got it, I got it, I got it.........Again! I found an elegant solution I think. A light bulb is starting shine!!!! Tell what you think about this solution. THis will allow me to use a static function. WOuld it be better to use an instance virtual function and have each derrived instance call the base.function instead?:

namespace ConsoleApplication1
{
class Program
{
static void Main(string[] args)
{
B objB = new B();
List<iclass> oBList = new List<iclass>();
List oList = A.GetList();
}
}

public interface iClass
{
string Full_Name
{
get;
set;
}
string Short_Name
{
get;
set;
}
}

public class A : iClass
{
public A()
{
}
private string _PhoneA = "";
private string _Full_Name = "";
private string _Short_Name = "";
public string PhoneA
{
get { return _PhoneA; }
set { _PhoneA = value; }
}

public static List<t> GetList<t>() where T : iClass, new()
{
T obj = new T();
List<t> result = new List<t>();
obj.Full_Name = "Susan";
obj.Short_Name = "Su";

if (typeof(T) == typeof(A))
{

(obj as A).PhoneA = "444-4444";
result.Add(obj);
}
else if (typeof(T) == typeof(B))
{
(obj as B).SSN = "123-12-1111";
result.Add(obj);
}
return result;

}

public string Full_Name
{
get { return _Full_Name; }
set { _Full_Name = value; }
}
public string Short_Name
{
get { return _Short_Name; }
set { _Short_Name = value; }
}

}

public class B : A, iClass
{
private string _SSN = "";
public string SSN
{
get { return _SSN; }
set { _SSN = value; }
}
}

}

Santiago Perez27-Jun-07 5:45

27-Jun-07 5:45

It works both ways!!! Generics is incredible!! It changes the whole game.
using System;
using System.Collections;
using System.Collections.Generic;
using System.Text;
using System.Collections.ObjectModel;

namespace ConsoleApplication1
{
class Program
{
static void Main(string[] args)
{
B objB = new B();
List<iclass> oBList = new List<iclass>();
List oList = A.GetList ();

List BList = new List();
objB.GetThisList(ref BList);
}

void GetNames()
{
Collection OBC = new Collection();
OBC.Add(new B());
}
}

public interface iClass
{
string Full_Name
{
get;
set;
}
string Short_Name
{
get;
set;
}
}

public class A : iClass
{
public A()
{
}
private string _PhoneA = "";
private string _Full_Name = "";
private string _Short_Name = "";
public string PhoneA
{
get { return _PhoneA; }
set { _PhoneA = value; }
}
public static void DoSomethingtoObject(iClass obj)
{
A objA = (A)obj;
objA.Full_Name = "Tom";
}
public static List<t> GetList<t>() where T : iClass, new()
{
T obj = new T();
List<t> result = new List<t>();
obj.Full_Name = "Susan";
obj.Short_Name = "Su";

if (typeof(T) == typeof(A))
{
(obj as A).PhoneA = "444-4444";
result.Add(obj);
}
else if (typeof(T) == typeof(B))
{
(obj as B).SSN = "123-12-1111";
result.Add(obj);
}
return result;

}

public virtual void GetThisList<t>(ref List<t> List) where T : iClass, new()
{
T objA = new T();
objA.Full_Name = "Mary J";
(objA as A).PhoneA = "123456";
List.Add(objA);
}

public string Full_Name
{
get { return _Full_Name; }
set { _Full_Name = value; }
}
public string Short_Name
{
get { return _Short_Name; }
set { _Short_Name = value; }
}

}

public class B : A, iClass
{
private string _SSN = "";
public string SSN
{
get { return _SSN; }
set { _SSN = value; }
}

public override void GetThisList<t>(ref List<t> List)
{
base.GetThisList<t>(ref List);
(List[0] as B).SSN = "123-11-1111";
}

}

}

Santiago Perez28-Jun-07 7:34

28-Jun-07 7:34

I found the solution I was looking for, thanks for your guidance Andy.
using System;
using System.Collections;
using System.Collections.Generic;
using System.Text;
using System.Collections.ObjectModel;
using Wintellect.PowerCollections;
using System.Collections.Specialized;
namespace ConsoleApplication1
{
class Program
{
static void Main(string[] args)
{
B objB = new B();
List<iclass> oBList = new List<iclass>();

List oList = A.GetList (); //Static function that evaluate typeof(T)
List BList = new List();
objB.GetThisList(ref BList); //Uses inheritance to call base.GetTHisList<>
}

public interface iClass
{
string Full_Name
{
get;
set;
}
string Short_Name
{
get;
set;
}
}

public class A : iClass
{
public A()
{
}
private string _PhoneA = "";
private string _Full_Name = "";
private string _Short_Name = "";
public string PhoneA
{
get { return _PhoneA; }
set { _PhoneA = value; }
}
public static void DoSomethingtoObject(iClass obj)
{
A objA = (A)obj;
objA.Full_Name = "Tom";
}
public static List<t> GetList<t>() where T : iClass, new()
{
T obj = new T();
List<t> result = new List<t>();
obj.Full_Name = "Susan";
obj.Short_Name = "Su";

if (typeof(T) == typeof(A))
{
(obj as A).PhoneA = "444-4444";
result.Add(obj);
}
else if (typeof(T) == typeof(B))
{
(obj as B).SSN = "123-12-1111";
result.Add(obj);
}
return result;

}

public virtual void GetThisList<t>(ref List<t> List) where T : iClass, new()
{
T objA = new T();
objA.Full_Name = "Mary J";
(objA as A).PhoneA = "123456";
List.Add(objA);
}

public string Full_Name
{
get { return _Full_Name; }
set { _Full_Name = value; }
}
public string Short_Name
{
get { return _Short_Name; }
set { _Short_Name = value; }
}

}

public class B : A, iClass
{
private string _SSN = "";
public string SSN
{
get { return _SSN; }
set { _SSN = value; }
}

public override void GetThisList<t>(ref List<t> List)
{
base.GetThisList<t>(ref List);
(List[0] as B).SSN = "123-11-1111";
}

}

}

Regards,
Santiago "Saint" Perez
Florida's Turnpike Enterprise Santiago.perez@dot.state.fl.us

Andy L 229-Jun-07 5:33