C# Discussion Boards - CodeProject

12-Nov-05 9:14

Consider the following code:

public class A
{
    private int x = 0;
    public int X
    {
        get
        {
            return x;
        }
        set
        {
            x = value;
        }
    }
    public override string ToString()
    {
        return x.ToString();
    }
}

public class B
{
    private ArrayList list = new ArrayList();

    private void addItem( A c )
    {
        list.Add(c);
    }
    private void changeItem ( ArrayList l )
    {
        ((A)l[0]).X = 5;
    }
    public void test()
    {
        addItem( new A());
        Console.WriteLine(list[0]);
        changeItem(list);
        Console.WriteLine(list[0]);
    }
    public static void Main( string[] args )
    {
        B b = new B();
        b.test();
    }
}

The output is:

0
5

Why the output not like:

0
0

changeItem method does not take the reference of the ArrayList, but the value of the object in the collection has changed OMG | :OMG:

What is the problem ?

Joshua Quick12-Nov-05 10:04

12-Nov-05 10:04

Kamrul Hasan wrote:
changeItem method does not take the reference of the ArrayList, but the value of the object in the collection has changed What is the problem ?

Actually, changeItem() is taking the reference to your ArrayList member variable. Look again in your test() code. You're passing a reference to ArrayList member variable "list" into changeItem().

<br />
public void test()<br />
{<br />
   addItem( new A());<br />
   Console.WriteLine(list[0]);<br />
   changeItem(list);          // You are passing it here!<br />
   Console.WriteLine(list[0]);<br />
}<br />

Kamrul Hasan12-Nov-05 22:33

12-Nov-05 22:33

Thanks for your reply.
In which cases 'ref' keyword should be used? I am confused Confused | :confused:

As your answer the following two methods will do the same thing isn't it?
1.changeItem( ref ArrayList l )
or
2.changeItem( ArrayList l )

Joshua Quick12-Nov-05 23:00

12-Nov-05 23:00

Member variable "list" is a reference to the ArrayList object and not the object itself. The important thing you need to learn here is the difference between "reference types" and "value types".

All classes such as ArrayList are reference types. Class objects are created via "new" and they only exist in the heap (not the stack). "new" merely returns a reference to that new object. So, when you pass an object reference to a function, you are merely passing a copy of that reference and not a copy of that object.

All structures such as int, long, and float are value types. These types are created on the stack and are not referenced. And yes, they really are structures. int maps to the System.Int32 structure. float maps to the System.Single structure.
So, when you pass a value type into a function, you are passing a copy of its data.

I'm not sure what your goal is here, but if you want to pass a copy of your ArrayList object into your changeItem() function, then you're going to need to clone it. Cloning an object will create a new object having the same object data.

changeItem((ArrayList)list.Clone());

I hope this helps!

S. Senthil Kumar13-Nov-05 4:55

S. Senthil Kumar

13-Nov-05 4:55

Just in case the OP misses it, only the ArrayList is cloned, not the elements in that list.

Regards
Senthil
_____________________________
My Blog | My Articles | WinMacro

Joshua Quick13-Nov-05 10:02

13-Nov-05 10:02

Since the ArrayList contains integers (ie: value types), it should be copied ok.
But good point to bring up. If it stored reference types, then they'll need to be cloned too.

Grouping Radio Buttons

Kamrul Hasan12-Nov-05 8:33

Re: Grouping Radio Buttons

12-Nov-05 8:33

Is there any way to group several radio buttons without putting them into a GroupBox ?

Joshua Quick12-Nov-05 10:09

Re: Grouping Radio Buttons

12-Nov-05 10:09

You can only have one grouping of RadioButtons per Form, GroupBox, or Panel. If you want to have several groupings that look like they're on the same form, then I suggest you put them inside borderless Panels.

da vinci coder13-Nov-05 12:03

da vinci coder

13-Nov-05 12:03

Set the Groupnames same with the other radiobuttons

<asp:radiobutton id="RadioButton1" style="Z-INDEX: 101; LEFT: 256px; POSITION: absolute; TOP: 184px"
="" runat="server" <b="">GroupName="a">
<asp:radiobutton id="RadioButton2" style="Z-INDEX: 102; LEFT: 256px; POSITION: absolute; TOP: 224px"
="" runat="server" <b="">GroupName="a">
<asp:radiobutton id="RadioButton3" style="Z-INDEX: 103; LEFT: 440px; POSITION: absolute; TOP: 192px"
="" runat="server" <b="">GroupName="b">
<asp:radiobutton id="RadioButton4" style="Z-INDEX: 104; LEFT: 448px; POSITION: absolute; TOP: 232px"
="" runat="server" <b="">GroupName="b">

ReadOnly Radio Button?

rich_wenger12-Nov-05 8:25

12-Nov-05 8:25

Hi,

Anybody have any ideas on how to best emulate a 'ReadOnly' capability for a radio button? Any help greatly appreciated.

Colin Angus Mackay12-Nov-05 8:28

Colin Angus Mackay

12-Nov-05 8:28

Enabled = false

My: Blog | Photos

"Man who stand on hill with mouth open will wait long time for roast duck to drop in." -- Confucious

rich_wenger12-Nov-05 12:03

12-Nov-05 12:03

I'm doing that already. Looks like sh*t.

Kamrul Hasan12-Nov-05 22:42

12-Nov-05 22:42

Your problem statement is not clear. Can you explain it a bit more ?

rich_wenger13-Nov-05 3:13

13-Nov-05 3:13

Hi,

Thanks for your interest. I have a data application in which some boolean choices as represented by radio button pairs and at certain points in the application I am representing the data to the user in ReadOnly TextBoxes where applicable. I would like to emulate this functionality in a representation of the RadioButton and am looking for a path of least resistance to accomplish this task. Any help would be greatly appreciated.

Dan Neely14-Nov-05 2:10

Dan Neely

14-Nov-05 2:10

Change the font color back to black after disabling the button?

rich_wenger14-Nov-05 4:50

14-Nov-05 4:50

I've taken a different approach by building my own custom control that inherits from System.Windows.Forms.RadioButton NameSpace. I'm using GDI+ to alter the presentation of the interface based off a boolean public property I've exposed called 'ReadOnly'. I'm still trying to workout how to cancel 'Click' the click event. Any help would be greatly appreciated.

Kamrul Hasan14-Nov-05 6:24

14-Nov-05 6:24

You can stop the click Event by overriding the OnClick method in RadioButton class and Removing the call to the base class. like:

protected override void OnClick(System.EventArgs e)<br />
{<br />
//base.OnClick (e);<br />
}<br />

-- modified at 12:27 Monday 14th November, 2005

rich_wenger14-Nov-05 8:44

14-Nov-05 8:44

Hi, and thanks for your interest. I tried your suggestion but when I tried to build the control I received an error 'RadioButtonRocLib.RadioButtonRoc.onclick(System.EventArgs)': no suitable method found to override".

Kamrul Hasan15-Nov-05 2:12