How to make public function if else for textbox? [on hold]

Here is my example code for if else textbox, my goal is want to make these if else as a public function. So when i want to use these function in other form i just called the public function. Thankyou

private void button1_Click(object sender, EventArgs e)
    {
        if (textBox1.Text == "" || textBox2.Text == "")
        {
            MessageBox.Show("Field cannot be empty");
        }
        else if (textBox1.Text != "admin" && textBox2.Text != "admin")
        {
            MessageBox.Show("Login invalid");
        }
        else
        {
            MessageBox.Show("Login success");
        }
    }