Doubt regarding System.windows.Form.Control

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Hi all,

I have seen a code as shown below

C#

Class Sample
      {
           AddSubPage("Title",new ServerControl());
           private void AddSubPage(string title, Control subPage)
           {
          
           }
      };
      Class ServerControl
      {
         public ServerControl()
         {
             InitializeComponent();
         }
      };

My doubt is regarding the second parameter.What is actually passing in the

second parameter.I know 'Control' is the base class of all controls in form.So how

to assign new ServerControl() to Control object.

'new ServerControl()' means just calling a constructor.(See the code).Then what is

actually passing here.

Note:Class ServerControl is inherits a class called DBMigrationSubPageBase which

inherits a class 'UserControl'

Thanks in advance

Posted 27-Nov-11 19:08pm

kutz 2

Updated 27-Nov-11 19:11pm

Manoj K Bhoir

v2

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Manoj K Bhoir 28-Nov-11 1:12am

Edited to add <pre> tag.

1 solution

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Wayne Gaylard · Accepted Answer · 2011-11-27T19:41:00

What gets passed to AddSubPage is an instance of whatever type you call the method with, as long as it derives from Control. If not, the compiler will throw an error. Once it has been passed, you will have to explicitly convert to the type of control actually passed.

If you do a quick test, something like this:-

C#

public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
            AddServerControl("New Server Control", new ServerControl());
        }

        void AddServerControl(string title, Control subpage)
        {
            //Should do checking here to ensure it is Server control.
            ServerControl ctrl = subpage as ServerControl;
            ctrl.Talk("I am a Server control!");
        }
    }

    class ServerControl:Control
    {
        public ServerControl()
        {

        }

        public void Talk(string message)
        {
            MessageBox.Show(message);
        }
    }

you will see that the messagebox is displayed, which means that the object passed IS actually an instance of ServerControl.

Hope this helps