Need help with calling one class from another

[d.s.]

I've got an app with two classes, and one class (InventoryInfoC lass)
is an object within the other class (InventoryItem) . I'm running into
problems with trying to access (get/set) a private variable within the
included class (InventoryInfo) from the "including" class
(InventoryItem) .

Here's the code, trimmed down. I've included ********* at the start
of the first line that's blowing up on me. I'm sure others that try
to access the invInfo.company Name field will blow up too.

Any help please?

------------------------------------------------------------------------------------------

using System;
using System.Collecti ons.Generic;
using System.Linq;
using System.Text;
using System.IO;

namespace InventoryInfo
{
public class InventoryInfoCl ass
{
private string _companyName;
public InventoryInfoCl ass()
{
companyName = "";

}

public string companyName
{
get
{
return _companyName;
}
set
{
_companyName = value;
}
}

}

public class InventoryItem
{
private InventoryInfoCl ass invInfo;
private string _itemID;

public InventoryItem()
{
InventoryInfoCl ass invInfo = new InventoryInfoCl ass();
_itemID = "";

}

public string itemID
{
get
{
return _itemID;
}
set
{
_itemID = value;
}

}
public string companyName
{
get
{
********* return invInfo.company Name;
}

set
{
invInfo.company Name = value;
}
}
public void printInvItem()
{

Console.WriteLi ne("Company Name: {0}", this.companyNam e);
Console.WriteLi ne("Item ID: {0}", this.itemID);

Console.WriteLi ne("Press any key to continue");
Console.ReadLin e();

}

}
class InvApp
{
static void Main(string[] args)
{
InventoryItem invItem = new InventoryItem() ;

invItem.printIn vItem();

invItem.company Name = "C";

invItem.printIn vItem();
}

}

}

[salman]

I am feeling that every InventoryItem have an InventoryInfoCl ass, (or
in other words, every InventoryItem object have a company name) its
means InventoryInfoCl ass can be a base class for all items.

So you should change your model and inherit InventoryItem from
InventoryInfoCl ass, then all the private members of InventoryInfoCl ass
will be accessible in InventoryItem.
Ali
On Jul 21, 9:22*am, "d.s." <nodamnspa...@y ahoo.comwrote:

I've got an app with two classes, and one class (InventoryInfoC lass)
is an object within the other class (InventoryItem) . *I'm running into
problems with trying to access (get/set) a private variable within the
included class (InventoryInfo) *from the "including" class
(InventoryItem) .

Here's the code, trimmed down. *I've included ********* at the start
of the first line that's blowing up on me. *I'm sure others that try
to access the invInfo.company Name field will blow up too.

Any help please?

------------------------------------------------------------------------------------------

using System;
using System.Collecti ons.Generic;
using System.Linq;
using System.Text;
using System.IO;

namespace InventoryInfo
{
* * public class InventoryInfoCl ass
* * {
* * * * private string _companyName;

* * * * public InventoryInfoCl ass()
* * * * {
* * * * * * companyName = "";

* * * * }

* * * * public string companyName
* * * * {
* * * * * * get
* * * * * * {
* * * * * * * * return _companyName;
* * * * * * }
* * * * * * set
* * * * * * {
* * * * * * * * _companyName = value;
* * * * * * }
* * * * }

* * }

* * public class InventoryItem
* * {
* * * * private InventoryInfoCl ass invInfo;
* * * * private string _itemID;

* * * * public InventoryItem()
* * * * {
* * * * * * InventoryInfoCl ass invInfo = new InventoryInfoCl ass();
* * * * * * _itemID = "";

* * * * }

* * * * public string itemID
* * * * {
* * * * * * get
* * * * * * {
* * * * * * * * return _itemID;
* * * * * * }
* * * * * * set
* * * * * * {
* * * * * * * * _itemID = value;
* * * * * * }

* * * * }

* * * * public string companyName
* * * * {
* * * * * * get
* * * * * * {
********* * * * return invInfo.company Name;
* * * * * * }

* * * * * * set
* * * * * * {
* * * * * * * * invInfo.company Name = value;
* * * * * * }
* * * * }

* * * * public void printInvItem()
* * * * {

* * * * * * Console.WriteLi ne("Company Name: {0}", this.companyNam e);
* * * * * * Console.WriteLi ne("Item ID: {0}", this.itemID);

* * * * * * Console.WriteLi ne("Press any key to continue");
* * * * * * Console.ReadLin e();

* * * * }

* * }

* * class InvApp
* * {
* * * * static void Main(string[] args)
* * * * {
* * * * * * InventoryItem invItem = new InventoryItem() ;

* * * * * * invItem.printIn vItem();

* * * * * * invItem.company Name = "C";

* * * * * * invItem.printIn vItem();
* * * * }

* * }

}

[Peter Duniho]

On Sun, 20 Jul 2008 21:22:38 -0700, d.s. <no**********@y ahoo.comwrote:

I've got an app with two classes, and one class (InventoryInfoC lass)
is an object within the other class (InventoryItem) . I'm running into
problems with trying to access (get/set) a private variable within the
included class (InventoryInfo) from the "including" class
(InventoryItem) .

First, the code you posted should work. The line you say doesn't work
isn't accessing the private field, but rather a public property. Can we
assume that the code you posted isn't in fact the code that you're having
trouble with?

I admit, from the code you posted, it's not obvious to me why you have the
nested class anyway. The outer, containing class is just proxying the
value to the nested class anyway. Why not just put that data in the
containing class?

That said, the issue you're seeing is a basic rule about nested classes:
the nested class can see "private" members of the containing class, but
not the other way around. That is, since the nested class is effectively
a member the containing class, it has access to everything _any_ member of
the containing class would, including all private members of the
containing class. But the containing class is most certainly not a member
of the nested class, and only the members of the nested class can access
private members.

Personally, I don't see the problem here. I don't know why you want the
nested class in the first place, but assuming you do, why not just use the
public property as you've defined it, rather than trying to get at the
private field? That's a better encapsulation anyway.

If you can elaborate on what code is actually not working, and why it is
you think your containing class should have access to private members of
the nested class, perhaps we can offer different advice more suitable to
your goals (assuming the above doesn't do it).

Pete

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

d.s. wrote:

I've got an app with two classes, and one class (InventoryInfoC lass)
is an object within the other class (InventoryItem) . I'm running into
problems with trying to access (get/set) a private variable within the
included class (InventoryInfo) from the "including" class
(InventoryItem) .

Here's the code, trimmed down. I've included ********* at the start
of the first line that's blowing up on me. I'm sure others that try
to access the invInfo.company Name field will blow up too.

Any help please?

8< snip

>
public class InventoryItem
{
private InventoryInfoCl ass invInfo;
private string _itemID;

public InventoryItem()
{
InventoryInfoCl ass invInfo = new InventoryInfoCl ass();

Here you have declared a local variable with the same name as the member
variable. The local variable gets assigned the new info object, but the
member variable remains null.

_itemID = "";

}

8< snip

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

[d.s.]

On Jul 20, 11:49*pm, "Peter Duniho" <NpOeStPe...@nn owslpianmk.com>
wrote:

On Sun, 20 Jul 2008 21:22:38 -0700, d.s. <nodamnspa...@y ahoo.comwrote:

I've got an app with two classes, and one class (InventoryInfoC lass)
is an object within the other class (InventoryItem) . *I'm running into
problems with trying to access (get/set) a private variable within the
included class (InventoryInfo) *from the "including" class
(InventoryItem) .

First, the code you posted should work. *The line you say doesn't work *
isn't accessing the private field, but rather a public property. *Can we *
assume that the code you posted isn't in fact the code that you're having*
trouble with?

I agree it should work, but it is bombin on me. It is the code, but
it's trimmed way down, getting rid of other variables and their
accessors.

>
I admit, from the code you posted, it's not obvious to me why you have the *
nested class anyway. *The outer, containing class is just proxying the *
value to the nested class anyway. *Why not just put that data in the *
containing class?

Ths was a homework assignment. It has already been submitted, so
you're not doing my work for me. But I need to understand what went
wrong because other assignments will build on this. The teacher seems
to be having a bit of a problem responding to requests for help
(online class).

So, the assignment was to do it as done here. The next assignment was
to inherit the InventoryInfo class, which worked with no problems.

That said, the issue you're seeing is a basic rule about nested classes: *
the nested class can see "private" members of the containing class, but *
not the other way around. *That is, since the nested class is effectively *
a member the containing class, it has access to everything _any_ member of *
the containing class would, including all private members of the *
containing class. *But the containing class is most certainly not a member *
of the nested class, and only the members of the nested class can access *
private members.

But it should be able to use the accessors to gain access to the
private variables. Perhaps my terminology is wrong. I'm trying to
use the accessor, and it's blowing up:

********* return invInfo.company Name;

>
Personally, I don't see the problem here. *I don't know why you want the *
nested class in the first place, but assuming you do, why not just use the *
public property as you've defined it, rather than trying to get at the *
private field? *That's a better encapsulation anyway.

I am trying to use the accessor to gain access to the private field.

********* return invInfo.company Name;

but it doesn't like it.

>
If you can elaborate on what code is actually not working, and why it is *
you think your containing class should have access to private members of *
the nested class, perhaps we can offer different advice more suitable to *
your goals (assuming the above doesn't do it).

The line I put the asterisks on is the first line that bombs in my
compiler.

If the contained class is to access the elements of the container
class, this means I will need to change the contained class everytime
I want to include it into a different container class that has
different elements.

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

d.s. wrote:

>First, the code you posted should work. The line you say doesn't work
isn't accessing the private field, but rather a public property. Can we
assume that the code you posted isn't in fact the code that you're having
trouble with?

I agree it should work, but it is bombin on me.

No, it should not work. Se my other post in the thread.

>If you can elaborate on what code is actually not working, and why it is
you think your containing class should have access to private members of
the nested class, perhaps we can offer different advice more suitable to
your goals (assuming the above doesn't do it).

The line I put the asterisks on is the first line that bombs in my
compiler.

Are you completely sure about that? It compiles just fine for me, but I
get a runtime exception on exactly that line because the invInfo member
variable is null.

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

[d.s.]

On Jul 21, 3:01 am, Göran Andersson <[e-mail] mwrote:

d.s. wrote:

First, the code you posted should work. The line you say doesn't work
isn't accessing the private field, but rather a public property. Can we
assume that the code you posted isn't in fact the code that you're having
trouble with?

I agree it should work, but it is bombin on me.

No, it should not work. Se my other post in the thread.

If you can elaborate on what code is actually not working, and why it is
you think your containing class should have access to private members of
the nested class, perhaps we can offer different advice more suitable to
your goals (assuming the above doesn't do it).

The line I put the asterisks on is the first line that bombs in my
compiler.

Are you completely sure about that? It compiles just fine for me, but I
get a runtime exception on exactly that line because the invInfo member
variable is null.

--
Göran Andersson
_____http://www.guffa.com

I'll check that out. The error message I got back was not very
helpful. Yes, it did compile for me. It was a runtime error.
Thanks. I'll check it.

[Peter Duniho]

On Mon, 21 Jul 2008 02:27:14 -0700, d.s. <no**********@y ahoo.comwrote:

I agree it should work, but it is bombin on me. It is the code, but
it's trimmed way down, getting rid of other variables and their
accessors. [...]

Ah, I see where I misread. Your use of the word "including" misdirected
me and I incorrectly read the "Info" class as being nested.

Also, next time you post a question, please avoid vague terms like "blow
up" and "bombin [sic] on me". It doesn't help that one post claims it was
a compiler error, but more broadly you simply need to post a precise
description of the error.

I apologize for any confusion...as is sometimes the case, trying to answer
questions very late at night caused me to overlook pretty much all of the
important parts of the code, relying too much on your description of the
problem.

Anyway, Göran has the answer for you. You should read his post.

Pete

[d.s.]

On Jul 21, 3:01*am, Göran Andersson <[e-mail] mwrote:

d.s. wrote:

First, the code you posted should work. *The line you say doesn't work *
isn't accessing the private field, but rather a public property. *Can we *
assume that the code you posted isn't in fact the code that you're having *
trouble with?

I agree it should work, but it is bombin on me.

No, it should not work. Se my other post in the thread.

If you can elaborate on what code is actually not working, and why it is *
you think your containing class should have access to private members of *
the nested class, perhaps we can offer different advice more suitable to *
your goals (assuming the above doesn't do it).

The line I put the asterisks on is the first line that bombs in my
compiler.

Are you completely sure about that? It compiles just fine for me, but I
get a runtime exception on exactly that line because the invInfo member
variable is null.

--
Göran Andersson
_____http://www.guffa.com

I set the invInfo member variable to non-null. And not it blows up on
the set accessor when I try to change it. Also, when I hover over
invInfo on that line, it shows NULL.

[d.s.]

On Jul 21, 8:38*am, "Peter Duniho" <NpOeStPe...@nn owslpianmk.com>
wrote:

On Mon, 21 Jul 2008 02:27:14 -0700, d.s. <nodamnspa...@y ahoo.comwrote:

I agree it should work, but it is bombin on me. *It is the code, but
it's trimmed way down, getting rid of other variables and their
accessors. *[...]

Ah, I see where I misread. *Your use of the word "including" misdirected *
me and I incorrectly read the "Info" class as being nested.

Also, next time you post a question, please avoid vague terms like "blow *
up" and "bombin [sic] on me". *It doesn't help that one post claims it was *
a compiler error, but more broadly you simply need to post a precise *
description of the error.

Sorry. I was at home, without the code in front of me, and was just
posting from memory.

>
I apologize for any confusion...as is sometimes the case, trying to answer *
questions very late at night caused me to overlook pretty much all of the*
important parts of the code, relying too much on your description of the *
problem.

You also have a novice over here, to c# anyway.