Ambiguous Method Of Show And ShowDialog For Displaying Winform

Question

I am struggling between Show and ShowDialog method of Showing/Display of Window Form. I am generally use show method instead of ShowDialog method. And ShowDialog Method is utilize when I don't want to show the forms at ALT+TAB ToolWindow.
The ShowDialog method is shows model window form which is having limited access than normal window form. The model window form is not accessing value of control and object which already passed on normal window form hence We have to provide the new value on each time or every time of new instance of forms which's real example is as under.
//Purchase_Entry having a public method which is calling from form30 as under:

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


 public void Purchase_Binding()
 {
        mydgv.Location = new Point(0, 110);
        mydgv.RowHeadersVisible = false;
        mydgv.Width = panel2.Width;
        mydgv.Height = panel2.Height - 220;
        mydgv.TabIndex = 4;


        string connstr = "server=.;initial catalog=maa;uid=mah;pwd=mah";
        SqlConnection con = new SqlConnection(connstr);
        con.Open();

        string sql = @"select billno,date=convert(varchar,date,103),ledgeraccount,totcts,rround,grosspurchase,taxes,taxamt,totdb,narrat" +
                     " from depurchasea where companyID=@companyID" +
                     " and transID=@transID" +
                     " group by billno,date,ledgeraccount,totcts,rround,grosspurchase,taxes,taxamt,totdb,narrat" +
                     " order by date,billno";


        SqlCommand cmd = new SqlCommand(sql, con);
        cmd.Parameters.AddWithValue("companyID", label6.Text);
        cmd.Parameters.AddWithValue("transID", textBox5.Text);
        SqlDataAdapter dap = new SqlDataAdapter(cmd);
        DataSet ds = new DataSet();
        dap.Fill(ds);
        for (int i = 0; i < ds.Tables[0].Rows.Count; i++)
        {
            textBox2.Text       = Convert.ToString(ds.Tables[0].Rows[i]["billno"]);
            maskedTextBox1.Text = Convert.ToString(ds.Tables[0].Rows[i]["date"]);
            textBox1.Text       = Convert.ToString(ds.Tables[0].Rows[i]["ledgeraccount"]);
            textBox9.Text       = Convert.ToString(ds.Tables[0].Rows[i]["totcts"]);
            textBox7.Text       = Convert.ToString(ds.Tables[0].Rows[i]["rround"]);
            textBox13.Text      = Convert.ToString(ds.Tables[0].Rows[i]["grosspurchase"]);
            comboBox1.Text      = Convert.ToString(ds.Tables[0].Rows[i]["taxes"]);
            textBox8.Text       = Convert.ToString(ds.Tables[0].Rows[i]["taxamt"]);
            textBox6.Text       = Convert.ToString(ds.Tables[0].Rows[i]["totdb"]);
            textBox3.Text       = Convert.ToString(ds.Tables[0].Rows[i]["narrat"]);
        }

        //mydgv.Columns.Clear();

        string mysql = "select srno,particulars,carats,rate,debit from depurchasea" +
                     " where companyID=@companyID" +
                     " and transID=@transID";
        SqlCommand mycmd = new SqlCommand(mysql, con);
        mycmd.Parameters.AddWithValue("companyID", label6.Text);
        mycmd.Parameters.AddWithValue("transID", textBox5.Text);
        SqlDataAdapter mydap = new SqlDataAdapter(mycmd);
        DataSet myds = new DataSet();
        mydap.Fill(myds);
        mybinding = new BindingSource();
        mybinding.DataSource = myds;
        mybinding.DataMember = myds.Tables[0].TableName;
        mydgv.DataSource = mybinding;

mydgv.Columns[0].HeaderText = "Sr.No.";
        mydgv.Columns[1].HeaderText = "Particulars";
        mydgv.Columns[2].HeaderText = "Carats";
        mydgv.Columns[3].HeaderText = "Rate";
        mydgv.Columns[4].HeaderText = "Amount";


        mydgv.Columns[0].Width = 50;
        mydgv.Columns[1].Width = 500;
        mydgv.Columns[4].Width = 100;
        mydgv.Columns[2].Width = 100;
        mydgv.Columns[3].Width = 100;

        mydgv.Columns[2].DefaultCellStyle.Alignment = DataGridViewContentAlignment.BottomRight;
        mydgv.Columns[3].DefaultCellStyle.Alignment = DataGridViewContentAlignment.BottomRight;
        mydgv.Columns[4].DefaultCellStyle.Alignment = DataGridViewContentAlignment.BottomRight;
        mydgv.Columns[2].DefaultCellStyle.Format = "f2";
        mydgv.Columns[3].DefaultCellStyle.Format = "f2";
        mydgv.Columns[4].DefaultCellStyle.Format = "f2";
        mydgv.Columns[4].ReadOnly = true;

        int dgvsize = mydgv.Width / 17;
        mydgv.Columns[0].Width = dgvsize;
        mydgv.Columns[1].Width = dgvsize * 10;
        mydgv.Columns[2].Width = dgvsize * 2;
        mydgv.Columns[3].Width = dgvsize * 2;
        mydgv.Columns[4].Width = dgvsize * 2;
        mydgv.Refresh();


        if (textBox13.Text != "")
        {
            decimal res = Convert.ToDecimal(textBox13.Text);
            textBox13.Text = res.ToString("f2");
        }
    }


public partial class Form30 : Form
{
    public Form30()
    {
        InitializeComponent();
    }

 private void listView1_KeyPress(object sender, KeyPressEventArgs e)
 {
     else if (textBox2.Text == "Purchase")
     {
          purchase_Entry pc = new purchase_Entry();
          pc.lbl6.Text  = pp.Form1.IDD.Text; //companyID
          pc.Purchase_Binding() //Calling public method of purchase_entry Class
          pc.ShowDialog(this);
          pc.textboxKeypress += new purchase_Entry.Action(pc_textboxKeypress);
          pc.purkeydown += new purchase_Entry.Action(pc_purkeydown);

      }
  }


The Calling Purchase_Binding() method from purchase_Entry Form on Show() method is working very well but if I use the same at ShowDialog() method than it will display the records but the alignment of controls are changed. that's means I have to issue new value of each control size,height,width and companyID on instance showing at ShowDialog() Method.
If So than it will donkey works for me.because I have to redesign purchase_Entry on ShowDialog() method.
What is the best way?. If I deal with Show() method than form will show at ALT+TAB ToolWindow and I don't want to allow to show it at ALT+TAB ToolWindow that's why I am used ShowDialog() Methodwhich will showing as model window form and will not displaying at ALT+TAB ToolWindow.
And If I use the ShowDialog() method than I have to be ready to redesign it like donkey works. Isn't It?.