Returning data to Forms without opening a new instance

Question

I am trying to return some data from Form2 to Form1, everything seems fine, I got the data and so, but, when I try to pass my data to a textbox, it doesn't changes the text. Only if I open a new instance of Form1, on Form2 it works. Why this happen? Can't I send the text to the old instance?

I'm using this code;

Form1 (Main Form)

public void updateText(string data)
{
    MessageBox.Show(data);
    txtGood.Text = data;
}

Form2 SecondaryForm = new Form2();

SecondaryForm.ShowDialog();

Form2 (Second Form with user data)

Form1 MainForm = new Form1();
MainForm.updateText(data);
MainForm.ShowDialog();
this.Close();

So, my question is, how can I pass the data values to the old instance of the main form? without having to create a new instance and show a new instance. Is there a way to do this?

Answer 1

What you can do is pass the reference of MainForm(Form1) to second Form(Form2). Then instead of creating MainForm again use the reference to update the textbox.

   //pass reference to form2
   Form2 SecondaryForm = new Form2(mainForm);
   SecondaryForm.ShowDialog();

    //in the constructor of Form2 save the reference of Form1
    Form1 form1 = null

    Form2(Form1 mainForm)
    {
        form1 = mainForm;
    }

    //then instead of creating a new MainForm again just use reference of Form1

    form1.updateText(data);
    this.Close()