มี winform 3 form

private void button1_Click(object sender, EventArgs e)Form2 f = new Form2();

{

f.ShowDialog();

private void button1_Click(object sender, EventArgs e)this.Close(); หรือ this.Hide();Form1. f1 = new Form1();Form3 f3 = new Form3();

{

f1.Close(); หรือ this.Hide();

f3.Show();

ลองแบบนี้ดูครับ รักษา form 1 ไว้ไม่ให้ปิดตัวเอง เมื่อปิดก็ซ่อนพอ

// Form 1

    public partial class Form1 : Form
    {
        public Form3 f3;

        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            Form2 f2 = new Form2();
            f2.FormClosed += new FormClosedEventHandler(f2_FormClosed);
            f2.Show();
        }

        private void f2_FormClosed(object sender, FormClosedEventArgs e)
        {
            f3 = new Form3();
            f3.FormClosed += new FormClosedEventHandler(f3_FormClosed);
            f3.Show();
            this.Hide();
        }

        private void f3_FormClosed(object sender, FormClosedEventArgs e)
        {
            this.Show();
        }
    }

// Form 2

    public partial class Form2 : Form
    {
         public Form2()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            this.Close();
        }
    }