Question

If a Superclass has a function A() which changes a Label to “Hello World”. How can I get a subclass to call A() with the same result? As of now, I get no compile error, but the text won’t change!

Example code:

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();            
    }

    private void button1_Click(object sender, EventArgs e)
    {
        FunctionA("Hello");
    }  

    public void FunctionA(string s)
    {
        label1.Text = s;
    }

    private void button2_Click(object sender, EventArgs e)
    {
        Test t = new Test();
    }
}

class Test : Form1
{
    public Test()
    {
        FunctionA("World");
    }
}

Answer 1

Both the Forms must be having their own Label control to display messages. You might be using one Label to show the message which is not part of displaying Form.

I am not sure what are to trying to achieve but why don’t you just pass the Label control to FunctionA to modify the message this way:

public void FunctionA(ref Label lbl, string s)
{
    lbl.Text = s;
}

ADDED: You can do it this way:

1. First creating the instance of FormA.

   static void Main()
   {
       //...
       FormA frmA = new FormA();
       Application.Run(frmA);
   }
   

2. Passing the instance of FormA to FormB by exposing a parameterized constructor for any manipulation in FormA from within FormB.

   FormB frmB = new FormB(frmA);
   
   //...
   
   public partial class FormB : Form
   {
       public FormB()
       {
           InitializeComponent();
       }
   
       //parameterized constructor
       public FormB(FormA obj)
       {
           FormA = obj;
           InitializeComponent();
       }
   
       public FormA FormA { get; set; }   
   }