Programming Forums > Application Development > C#

OpenLoop · Oct 1st, 2005, 3:18 PM

I have two classes A and B. B inherits A, somthing like this

public Class A: Windows.Form
{
      private Button btn1;
      public TextBox txt1;
}
public Class B:A
{
      public TextBox txt2;
}

when i display form B, I get the button from A in addition to both text boxes. My questions is, how do i get B to inherit all of A's NON PRIVATE members only? (I don't want the button to show up in B)

Thank you

uman · Oct 1st, 2005, 6:25 PM

This isn't possible in C#. It is in C++, but that's another story.

OpenLoop · Oct 1st, 2005, 7:05 PM

I got a workarround. I created a BaseForm with no buttons and only the things i want common in all my forms. Then each new form inherts the base form.

I'm surprised C# doesn't have that capability, I guess you can't have anything.

Thanks for the info

xavier · Oct 1st, 2005, 11:33 PM

If the button is private , it means that it's only seen in its class, it will not be accesible in other classes ... So, how the hell did it show you the private button from A ?

Or am I misunderstanding the problem ?

If i have this :

(Toggle Plain Text)

	public class A
	{
		private static int i = 0;
		public static int t = 1;
	}

	public class B : A
	{
		public static int p = 2 ;
		public static void Main()
		{
			Console.WriteLine("i = {0} , t={1}, p={2}",i,t,p);
			Console.ReadLine();
		}
	}

It sais it can't access i because of its protection level.

OpenLoop · Oct 2nd, 2005, 1:00 PM

xavier, that's what i thought should happen, but it didn't. I guess it has to do with the nature of the program, being graphic and all. But like i said, i got arround it.

Dameon · Oct 2nd, 2005, 1:14 PM

A private member is still inherited. It just can't be accessed by subclasses.

(Toggle Plain Text)

class Person
{
private int age = 0;

public int Age
{
   get
   {
      return this.age;
   }
   set
   {
   if (value < 0)
      throw new Exception("A person can not have a negative age");
   this.age = value;
   }
}

}

class Employee : Person
{

   public void accessTest()
   {
      this.age = -5; //Can't do this, because age is private
      this.Age = -10 //Can do this, but it will throw an exception. See how private
                          //members can keep subclasses out of your business?
   }
}

A protected member can be accessed by subclasses (and I think nested classes). If age was protected, then both lines in accessTest would be valid.

When you inherited your form, notice that in both forms the constructor called InitializeComponent(). InitializeComponent is a private method for both forms. Because it is private, they can both exist without having a name conflict. Note that it is not being overriden. When you create an instance of your inherited form, the base constructor is called, and in turn the original InitializeComponent. This sets up the text box and the button. Then, the subclass constructor calls its InitializeComponent. This sets up the second text box.

xavier · Oct 2nd, 2005, 11:50 PM

The thing was, that i wrote a similar thingy to what OpenLoop described, but i forgot to initialize the button in the base class, so it didn't apear :o .

Thanks for the explanation Dameon.

Oct 1st, 2005, 3:18 PM	#1
OpenLoop Expert Programmer Join Date: May 2005 Location: East Lansing, MI Posts: 663 Rep Power: 4	Inheritance problem I have two classes A and B. B inherits A, somthing like this (Toggle Plain Text) public Class A: Windows.Form { private Button btn1; public TextBox txt1; } public Class B:A { public TextBox txt2; } public Class A: Windows.Form { private Button btn1; public TextBox txt1; } public Class B:A { public TextBox txt2; } when i display form B, I get the button from A in addition to both text boxes. My questions is, how do i get B to inherit all of A's NON PRIVATE members only? (I don't want the button to show up in B) Thank you

Oct 1st, 2005, 6:25 PM	#2
uman Expert Programmer Join Date: Dec 2004 Posts: 794 Rep Power: 4	This isn't possible in C#. It is in C++, but that's another story. __________________ Few people deserve to be compared to (Rush) Limbaugh, most of them were convicted at the Nuremburg trials. --WilliamSChips on Slashdot

Oct 1st, 2005, 11:33 PM	#4
xavier Professional Programmer Join Date: Oct 2004 Location: .ro Posts: 367 Rep Power: 4	If the button is private , it means that it's only seen in its class, it will not be accesible in other classes ... So, how the hell did it show you the private button from A ? Or am I misunderstanding the problem ? If i have this : (Toggle Plain Text) public class A { private static int i = 0; public static int t = 1; } public class B : A { public static int p = 2 ; public static void Main() { Console.WriteLine("i = {0} , t={1}, p={2}",i,t,p); Console.ReadLine(); } } public class A { private static int i = 0; public static int t = 1; } public class B : A { public static int p = 2 ; public static void Main() { Console.WriteLine("i = {0} , t={1}, p={2}",i,t,p); Console.ReadLine(); } } It sais it can't access i because of its protection level. __________________ Don't take life too seriously, it's not permanent !

Oct 2nd, 2005, 1:14 PM	#6
Dameon Troll Join Date: Apr 2005 Location: Texas Posts: 730 Rep Power: 4	A private member is still inherited. It just can't be accessed by subclasses. (Toggle Plain Text) class Person { private int age = 0; public int Age { get { return this.age; } set { if (value < 0) throw new Exception("A person can not have a negative age"); this.age = value; } } } class Employee : Person { public void accessTest() { this.age = -5; //Can't do this, because age is private this.Age = -10 //Can do this, but it will throw an exception. See how private //members can keep subclasses out of your business? } } class Person { private int age = 0; public int Age { get { return this.age; } set { if (value < 0) throw new Exception("A person can not have a negative age"); this.age = value; } } } class Employee : Person { public void accessTest() { this.age = -5; //Can't do this, because age is private this.Age = -10 //Can do this, but it will throw an exception. See how private //members can keep subclasses out of your business? } } A protected member can be accessed by subclasses (and I think nested classes). If age was protected, then both lines in accessTest would be valid. When you inherited your form, notice that in both forms the constructor called InitializeComponent(). InitializeComponent is a private method for both forms. Because it is private, they can both exist without having a name conflict. Note that it is not being overriden. When you create an instance of your inherited form, the base constructor is called, and in turn the original InitializeComponent. This sets up the text box and the button. Then, the subclass constructor calls its InitializeComponent. This sets up the second text box. __________________ MD5(sig) = bcef75433db02e9ad9bf81d6f7c5c270

Oct 2nd, 2005, 11:50 PM	#7
xavier Professional Programmer Join Date: Oct 2004 Location: .ro Posts: 367 Rep Power: 4	The thing was, that i wrote a similar thingy to what OpenLoop described, but i forgot to initialize the button in the base class, so it didn't apear :o . Thanks for the explanation Dameon. __________________ Don't take life too seriously, it's not permanent !

Oct 1st, 2005, 7:05 PM	#3
OpenLoop Expert Programmer Join Date: May 2005 Location: East Lansing, MI Posts: 663 Rep Power: 4	I got a workarround. I created a BaseForm with no buttons and only the things i want common in all my forms. Then each new form inherts the base form. I'm surprised C# doesn't have that capability, I guess you can't have anything. Thanks for the info

Oct 2nd, 2005, 1:00 PM	#5
OpenLoop Expert Programmer Join Date: May 2005 Location: East Lansing, MI Posts: 663 Rep Power: 4	xavier, that's what i thought should happen, but it didn't. I guess it has to do with the nature of the program, being graphic and all. But like i said, i got arround it.

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Programming Forums > Application Development > C#

Inheritance problem