How to pass a string from a Form in DataGridView of another Form?

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C#

Hello everyone,
I have two forms: Form1 contains a DataGridView and a Button - this Button uses to show Form2, there is abc() function in the Form1 . Form2 contains a Button to add a string to DataGridView of Form1. I code as follows (use delegate):
- Form1:

public void abc(string x)
        {
            dataGridView1.Rows.Add(x);
        }
 private void button1_Click(object sender, EventArgs e)
        {
            Form2 f = new Form2();
            f.Show();
        }

(abc() function is used to add string x to dataGridView1 of Form1)

- Form2:

public delegate void func(string x);
.........
private void button1_Click(object sender, EventArgs e)
        {
            func f = null;
            Form1 frm = new Form1();
            f = frm.abc;
            f("def");
        }

When I run, click to Button of Form1 then Form2 shows, after that I click to Button of Form2, but I don't see anything in dataGridView1 of Form1! How to do this? Thanks.