Question

public partial class Form1 : Form 
{

    public disp(string strVal)
     {
                   lbl1.text = strVal;
      }     

     private void button1_Click(object sender, EventArgs e)
            {

            class1 cl  = new class1;
            cl.Show1("test",this);

        }

}

—————- Class ————

public class class1

{
 private Form  frm1;

    public void  Show1(string xName , object xfrmObj)
    {
        frm1 = (form) xfrmObj;
        frm1.disp(xName );  // here I am getting error .
    }

}

——————————————/

here i am trying to access ‘disp’ function from class and i have pass ‘form1’ as a object , but i am getting error

The error message that I am getting is

Error 3
‘System.Windows.Forms.Form’ does not contain a definition for ‘disp’
and no extension method ‘disp’ accepting a first argument of type ‘System.Windows.Forms.Form’ could be found
(are you missing a using directive or an assembly reference?)

this syntax in vb.net is working perfect.

please help me…..

Rajesh.

Answer 1

you need to cast frm1 = (Form1)xfrmObj; instead of casting it to form in your Show1(xName,xfrmObj) method.

EDIT: OP has stated in a comment that he needs this to work for several different forms.
You can make all your forms implement the same Interface, like so:

public partial class Form1 : Form, ICanDisplay
{ 
    public void disp(string strVal) 
    { //...
    } 
}

public partial class Form2 : Form, ICanDisplay
{
    public void disp(string strVal) 
    { //...
    }
}

public interface ICanDisplay
{
    void disp(string strVal);
}

then, change your method so it casts to ICanDisplay:

public class class1
{
private Form  frm1;

public void Show1(string xName , object xfrmObj)
{
    frm1 = (ICanDisplay) xfrmObj;
    frm1.disp(xName);
}

}

However, as @Heinzi has noted, you should change your Show1-method to the following:

public void Show1(string xName, IDisplayForm xfrmObj)
{
    xfrmObj.Disp(xName);
}

this will make the cast entirely unnecessary. The next step is to select meaningful names for your variables, functions and classes.