473,241 Members | 1,633 Online
Bytes | Software Development & Data Engineering Community
Post Job

Home Posts Topics Members FAQ

Join Bytes to post your question to a community of 473,241 software developers and data experts.

Inhertance Question

Hi folks,

Take the following scenario:

public class BaseType {
}

public class DerivedTypeA : BaseType {

int _length;

public int Length {
get { return _length; } set { _length = value; }
}
}

public class DerivedTypeB : BaseType {

int _lowBound;
int _highBound;

public int LowBound {
get { return _lowBound; } set { _lowBound = value; }
}
}

public class BaseTypeCollection : BindingList<BaseType> {

}

An instance of the collection will contain various instances of the two
derived types and in the future many more derived types. At various
times I need to iterate through each item setting various values.

I can see a problem in that I still need to test within an iteration
routine the actual type of each instance, which to me sort of defeats
the reason for deriving from a base class in the first place.

Comments welcome.

Cheers

Simon
Dec 15 '05 #1
5 2124
Do you want to iterate over elements of specified type?

you can use smth like Dictionary<BaseType, BindingList<BaseType>>
then you will ask dictionary to return elements of specific type

--
Vadym Stetsyak aka Vadmyst
http://vadmyst.blogspot.com

"Simon" <si****************@nodomain.com> wrote in message
news:un**************@TK2MSFTNGP11.phx.gbl...
Hi folks,

Take the following scenario:

public class BaseType {
}

public class DerivedTypeA : BaseType {

int _length;

public int Length {
get { return _length; } set { _length = value; }
}
}

public class DerivedTypeB : BaseType {

int _lowBound;
int _highBound;

public int LowBound {
get { return _lowBound; } set { _lowBound = value; }
}
}

public class BaseTypeCollection : BindingList<BaseType> {

}

An instance of the collection will contain various instances of the two
derived types and in the future many more derived types. At various times
I need to iterate through each item setting various values.

I can see a problem in that I still need to test within an iteration
routine the actual type of each instance, which to me sort of defeats the
reason for deriving from a base class in the first place.

Comments welcome.

Cheers

Simon

Dec 15 '05 #2
I suppose what I'm getting at is:

Take my previous example but now add a method called Render() which each
subtype implements. This is great because I can call Render on any
BaseType derived instance but before I set or get data into any instance
I need to check what derivation it implements to make sure I am calling
a getter or setter that actualy exists.

This makes me think I am going to have big decision structures that will
need to be maintained every time I add a new derived type.

I know this isn't correct and I am missing something in the design.

I had the thought of adding virtual properties to the base type which do
nothing and then overriding when they are relevant.

For example, to flesh out my example.

public class BaseType {

public virtual Length {
get { return -1; } set { }
}

public virtual LowBound {
get { return -1; } set { }
}

public virtual HighBound {
get { return -1; } set { }
}

}

public class DerivedTypeA : BaseType {

int _length;

public override int Length {
get { return _length; } set { _length = value; }
}
}

public class DerivedTypeB : BaseType {

int _lowBound;
int _highBound;

public override int LowBound {
get { return _lowBound; } set { _lowBound = value; }
}

public override int HighBound {
get { return _highBound; } set { _highBound = value; }
}

public class BaseTypeCollection : BindingList<BaseType> {

}

This just seems wrong to me. It doesn't feel elegant.

Simon

Vadym Stetsyak wrote:
Do you want to iterate over elements of specified type?

you can use smth like Dictionary<BaseType, BindingList<BaseType>>
then you will ask dictionary to return elements of specific type

Dec 15 '05 #3
Hi Simon,
I can see a problem in that I still need to test within an iteration
routine the actual type of each instance, which to me sort of defeats the
reason for deriving from a base class in the first place.
There are many reasons to use inheritance, but your example is not an
example of one of them. A good example would be something like
System.Windows.Forms.Form, which is the base class for all forms. It
contains all the code necessary to create a container for Form UI controls.
To create a form, you simply inherit System.Windows.Forms.Form, and add the
Controls and logic to the new class that you need to create your
application.

By using a base class that has all the code needed to create a variety of
derived classes, redundancy is avoided, and maintenance of the common code
is done through just one implementation.

--
HTH,

Kevin Spencer
Microsoft MVP
..Net Developer
You can lead a fish to a bicycle,
but it takes a very long time,
and the bicycle has to *want* to change.

"Simon" <si****************@nodomain.com> wrote in message
news:un**************@TK2MSFTNGP11.phx.gbl... Hi folks,

Take the following scenario:

public class BaseType {
}

public class DerivedTypeA : BaseType {

int _length;

public int Length {
get { return _length; } set { _length = value; }
}
}

public class DerivedTypeB : BaseType {

int _lowBound;
int _highBound;

public int LowBound {
get { return _lowBound; } set { _lowBound = value; }
}
}

public class BaseTypeCollection : BindingList<BaseType> {

}

An instance of the collection will contain various instances of the two
derived types and in the future many more derived types. At various times
I need to iterate through each item setting various values.

I can see a problem in that I still need to test within an iteration
routine the actual type of each instance, which to me sort of defeats the
reason for deriving from a base class in the first place.

Comments welcome.

Cheers

Simon

Dec 15 '05 #4
"Simon" <si****************@nodomain.com> a écrit dans le message de news:
un**************@TK2MSFTNGP11.phx.gbl...

| An instance of the collection will contain various instances of the two
| derived types and in the future many more derived types. At various
| times I need to iterate through each item setting various values.
|
| I can see a problem in that I still need to test within an iteration
| routine the actual type of each instance, which to me sort of defeats
| the reason for deriving from a base class in the first place.

You need to look at the Visitor design pattern. It is intended to add
functionality to a hierarchy of classes without altering the code of the
clesses themselves. It also allows you to execute different code, depending
on the type of the item being visited.

public interface IVisitor
{
}

public interface IVisitable
{
void Accept(IVisitor visitor);
}

public class MyHierarchyVisitor : IVisitor
{
public MyHierarchyVisitor(...)
{
// pass parameters to internal fields for external objects that will be
used
// whilst visiting nodes in a list.
}

void VisitDerivedTypeA(DerivedTypeA node)
{
// do something specific to a DerivedTypeA object
}

void VisitDerivedTypeB(DerivedTypeB node)
{
// do something specific to a DerivedTypeB object
}
}

public abstract class BaseType : IVisitable
{
...

public abstract void Accept(IVisitor visitor);
}

public class DerivedTypeA : BaseType
{
...

public override void Accept(IVisitor visitor)
{
if (visitor is MyHierarchyVisitor)
((MyHierarchyVisitor) visitor).VisitDerivedTypeA(this);
}
}

public class DerivedTypeB : BaseType
{
...

public override void Accept(IVisitor visitor)
{
if (visitor is MyHierarchyVisitor)
((MyHierarchyVisitor) visitor).VisitDerivedTypeB(this);
}
}

Then you treat your list like this :

{
List<BaseType> items...

// add items to list

MyHierarchyVisitor visitor = new MyHierarchyVisitor(...);

foreach (IVisitable node in items)
node.Accept(visitor as IVisitor);
}

Joanna

--
Joanna Carter [TeamB]
Consultant Software Engineer
Dec 15 '05 #5
Ah nice one Joanna,

Gang of Four book open and I'm reading :)

Thanks again

Simon

Joanna Carter [TeamB] wrote:
"Simon" <si****************@nodomain.com> a écrit dans le message de news:
un**************@TK2MSFTNGP11.phx.gbl...

| An instance of the collection will contain various instances of the two
| derived types and in the future many more derived types. At various
| times I need to iterate through each item setting various values.
|
| I can see a problem in that I still need to test within an iteration
| routine the actual type of each instance, which to me sort of defeats
| the reason for deriving from a base class in the first place.

You need to look at the Visitor design pattern. It is intended to add
functionality to a hierarchy of classes without altering the code of the
clesses themselves. It also allows you to execute different code, depending
on the type of the item being visited.

public interface IVisitor
{
}

public interface IVisitable
{
void Accept(IVisitor visitor);
}

public class MyHierarchyVisitor : IVisitor
{
public MyHierarchyVisitor(...)
{
// pass parameters to internal fields for external objects that will be
used
// whilst visiting nodes in a list.
}

void VisitDerivedTypeA(DerivedTypeA node)
{
// do something specific to a DerivedTypeA object
}

void VisitDerivedTypeB(DerivedTypeB node)
{
// do something specific to a DerivedTypeB object
}
}

public abstract class BaseType : IVisitable
{
...

public abstract void Accept(IVisitor visitor);
}

public class DerivedTypeA : BaseType
{
...

public override void Accept(IVisitor visitor)
{
if (visitor is MyHierarchyVisitor)
((MyHierarchyVisitor) visitor).VisitDerivedTypeA(this);
}
}

public class DerivedTypeB : BaseType
{
...

public override void Accept(IVisitor visitor)
{
if (visitor is MyHierarchyVisitor)
((MyHierarchyVisitor) visitor).VisitDerivedTypeB(this);
}
}

Then you treat your list like this :

{
List<BaseType> items...

// add items to list

MyHierarchyVisitor visitor = new MyHierarchyVisitor(...);

foreach (IVisitable node in items)
node.Accept(visitor as IVisitor);
}

Joanna

Dec 15 '05 #6

This thread has been closed and replies have been disabled. Please start a new discussion.

Similar topics

4
by: Mohammed Mazid | last post by:
Can anyone please help me on how to move to the next and previous question? Here is a snippet of my code: Private Sub cmdNext_Click() End Sub Private Sub cmdPrevious_Click() showrecord
3
by: Stevey | last post by:
I have the following XML file... <?xml version="1.0"?> <animals> <animal> <name>Tiger</name> <questions> <question index="0">true</question> <question index="1">true</question> </questions>
7
by: nospam | last post by:
Ok, 3rd or is it the 4th time I have asked this question on Partial Types, so, since it seems to me that Partial Types is still in the design or development stages at Microsoft, I am going to ask...
3
by: Ekqvist Marko | last post by:
Hi, I have one Access database table including questions and answers. Now I need to give answer id automatically to questionID column. But I don't know how it is best (fastest) to do? table...
10
by: glenn | last post by:
I am use to programming in php and the way session and post vars are past from fields on one page through to the post page automatically where I can get to their values easily to write to a...
10
by: Rider | last post by:
Hi, simple(?) question about asp.net configuration.. I've installed ASP.NET 2.0 QuickStart Sample successfully. But, When I'm first start application the follow message shown. ========= Server...
53
by: Jeff | last post by:
In the function below, can size ever be 0 (zero)? char *clc_strdup(const char * CLC_RESTRICT s) { size_t size; char *p; clc_assert_not_null(clc_strdup, s); size = strlen(s) + 1;
56
by: spibou | last post by:
In the statement "a *= expression" is expression assumed to be parenthesized ? For example if I write "a *= b+c" is this the same as "a = a * (b+c)" or "a = a * b+c" ?
2
by: Allan Ebdrup | last post by:
Hi, I'm trying to render a Matrix question in my ASP.Net 2.0 page, A matrix question is a question where you have several options that can all be rated according to several possible ratings (from...
3
by: Zhang Weiwu | last post by:
Hello! I wrote this: ..required-question p:after { content: "*"; } Corresponding HTML: <div class="required-question"><p>Question Text</p><input /></div> <div...
0
by: abbasky | last post by:
### Vandf component communication method one: data sharing ​ Vandf components can achieve data exchange through data sharing, state sharing, events, and other methods. Vandf's data exchange method...
0
by: stefan129 | last post by:
Hey forum members, I'm exploring options for SSL certificates for multiple domains. Has anyone had experience with multi-domain SSL certificates? Any recommendations on reliable providers or specific...
1
by: davi5007 | last post by:
Hi, Basically, I am trying to automate a field named TraceabilityNo into a web page from an access form. I've got the serial held in the variable strSearchString. How can I get this into the...
0
by: MeoLessi9 | last post by:
I have VirtualBox installed on Windows 11 and now I would like to install Kali on a virtual machine. However, on the official website, I see two options: "Installer images" and "Virtual machines"....
0
by: DolphinDB | last post by:
The formulas of 101 quantitative trading alphas used by WorldQuant were presented in the paper 101 Formulaic Alphas. However, some formulas are complex, leading to challenges in calculation. Take...
0
by: Aftab Ahmad | last post by:
Hello Experts! I have written a code in MS Access for a cmd called "WhatsApp Message" to open WhatsApp using that very code but the problem is that it gives a popup message everytime I clicked on...
0
by: ryjfgjl | last post by:
ExcelToDatabase: batch import excel into database automatically...
0
isladogs
by: isladogs | last post by:
The next Access Europe meeting will be on Wednesday 6 Mar 2024 starting at 18:00 UK time (6PM UTC) and finishing at about 19:15 (7.15PM). In this month's session, we are pleased to welcome back...
0
isladogs
by: isladogs | last post by:
The next Access Europe meeting will be on Wednesday 6 Mar 2024 starting at 18:00 UK time (6PM UTC) and finishing at about 19:15 (7.15PM). In this month's session, we are pleased to welcome back...

By using Bytes.com and it's services, you agree to our Privacy Policy and Terms of Use.

To disable or enable advertisements and analytics tracking please visit the manage ads & tracking page.