Returning <List>

[Cralis]

I am trying to populate a ListView with a list of 'Models' of cars. I
have a data object class for my models, which has a function,
'getListOfModel s', which I want to retuyrn a <Listof models.

In my data object, I have also created a class to hold each model, as
shown below.

No database work has been done. Just adding a model, and trying to
return it.

class clsDOModels
{
public static List<ModelgetLi stOfModels()
{
SqlConnection sConn = clsDatabase.Get Connection();
List<Modelmodel s = new List<Model>();
Model mod = new Model();
mod.id = 1;
mod.description = "Raptor";
models.Add( mod );

return models;
}

}

class Model
{
public int id;
public string description;
}
My calling form does this:
ModelParts.clas ses.clsDOModels .getListOfModel s();

No runtime error, so it looks like it's working. My problem is, I'm
not sure how to get what ever is returned. That is, the <List>Models.
My calling form knows nothing about my 'Model' class from the data
object. So I am fundimentally doing something wrong, I think. How do I
declare what ever it is I am returning?

[Roman Wagner]

Hi,

try the following.

Write an interface (for example IModel) that defines everything about
a Model you need.
In your case it should look like

interface IModel
{
int ID { get; set; }
string Description { get; set; }
}

Your model class should implement the interface --class Model :
IModel

and you should return a list of IModel --public static List<IModel>
GetListOfModels ()

[Cralis]

Thanks Roman.

I'm pretty new to .Net and OOP, so excuse me here. Should this IModel
be in it's own class file?
At the moment, I have my class Model inside my clsDOModel (Model data
object class file). So should I have a separate file for Interfaces
maybe?

Also, once I have created the IModel interface, will it be visible to
my calling form?

[Ludwig]

On 18 May 2007 00:28:00 -0700, Cralis <ad***@myschool mates.comwrote:

>Thanks Roman.

I'm pretty new to .Net and OOP, so excuse me here. Should this IModel
be in it's own class file?
At the moment, I have my class Model inside my clsDOModel (Model data
object class file). So should I have a separate file for Interfaces
maybe?

Also, once I have created the IModel interface, will it be visible to
my calling form?

I mostly put interfaces even in their own project...

--
Ludwig
http://www.coders-lab.be

[Cralis]

Thanks guys. This sounds like a better plan, and I am learning
something new. :)

I guess you don't have to 'new' an interface, or do you?

I am getting a compiler error now. It says I can't create an instance
of an abstract class when I try "List<IModelmod els = new
List<IModel>(); "

namespace ModelParts.clas ses
{
class clsDOModels
{
public static List<IModelgetL istOfModels()
{
SqlConnection sConn = clsDatabase.Get Connection();
List<IModelmode ls = new List<IModel>();
IModel mod = new IModel();
mod.id = 1;
mod.description = "Raptor";
models.Add( mod );

return models;
}

}

interface IModel
{
int id { get; set;}
string description { get; set;}
bool deleted { get; set;}
}
}

[Marc Gravell]

If you form has acces to clsDOModels, then it has access to the Model
class (assuming that it is public) since they are side-by-side. You
should be able to use
List<Modelmodel s =
ModelParts.clas ses.clsDOModels .getListOfModel s();
Does this not work? I can't see how the compiler would let you near
getListOfModels () otherwise...?

Additionally - depending on your UI, it might not even be *necessary*
for the UI to know about the model (in the MVP sense, not the Model
class, although they amount to the same thing) - but it makes life a
lot easier if it does ;-p

Marc

[Cralis]

Oh!

I went and removed the class Model, and replaced it with interface!
This is where I am falling flat. So, I need to keep 'class Model' and
add : IModel to that.

I understand (I think)

[Ludwig]

>
First, you have the interface:

interface IModel
{
int id { get; set;}
string description { get; set;}
bool deleted { get; set;}
}

Then you have an implementation of you interface:

public class SomeModel : IModel
{
public string Description
{
get {return description;}
set {description = value;}
}

// same for id and deleted
}

Then you can:

SqlConnection sConn = clsDatabase.Get Connection();
List<IModelmode ls = new List<IModel>();
IModel mod = new Model(); <<-- the class, not interface
mod.id = 1;
mod.description = "Raptor";
models.Add( mod );

Note: properties start with capital letter (Pascal notation), private
variables with small letter (Camel notation)

there was an error:

SqlConnection sConn = clsDatabase.Get Connection();
List<IModelmode ls = new List<IModel>();
IModel mod = new SomeModel(); <<-- SomeModel !!
mod.id = 1;
mod.description = "Raptor";
models.Add( mod );

--
Ludwig
http://www.coders-lab.be

[=?ISO-8859-1?Q?G=F6ran_Andersson?=]

Cralis wrote:

I am trying to populate a ListView with a list of 'Models' of cars. I
have a data object class for my models, which has a function,
'getListOfModel s', which I want to retuyrn a <Listof models.

In my data object, I have also created a class to hold each model, as
shown below.

No database work has been done. Just adding a model, and trying to
return it.

class clsDOModels
{
public static List<ModelgetLi stOfModels()
{
SqlConnection sConn = clsDatabase.Get Connection();
List<Modelmodel s = new List<Model>();
Model mod = new Model();
mod.id = 1;
mod.description = "Raptor";
models.Add( mod );

return models;
}

}

class Model
{
public int id;
public string description;
}
My calling form does this:
ModelParts.clas ses.clsDOModels .getListOfModel s();

No runtime error, so it looks like it's working. My problem is, I'm
not sure how to get what ever is returned. That is, the <List>Models.
My calling form knows nothing about my 'Model' class from the data
object. So I am fundimentally doing something wrong, I think. How do I
declare what ever it is I am returning?

I would skip the ClassOfDataObje ctCreationClass ForClassModels class ;)
and just use a Model class, containing private member variables, public
properties and static methods to fetch the data:

public class Model {

private int _id;
private string _description;

public int Id { get { return _id; } }
public string Description { get { return _description; } }

public static List<ModelGetMo dels() {
List<Modelmodel s;
using (SqlConnection sConn = clsDatabase.Get Connection()) {
models = new List<Model>();
Model mod = new Model();
mod._id = 1;
mod._descriptio n = "Raptor";
models.Add( mod );
}
return models;
}

}

To get the return value of the method, just assign it's value to a variable:

List<Modelmodel s = Model.GetModels ();

--
Göran Andersson
_____
http://www.guffa.com

[Cralis]

Thanks very much to all of you. I'll work with the examples and advice
you have given, and see how far I get. THanks very much for your help
and time.