how to transfer data between form in wpf without opening new

I m transferring data from one WPF Window form (Form1) to another WPF Window form (Form2). but every time i transfer data from Form2 to Form1 i have to close and open Form1.

Please tell me alternate method so that i can transfer data without closing and openning the Form1

Here is my code :

FORM1:  

private void txtSellerCode_GotFocus(object sender, RoutedEventArgs e) 

{ 

SelectSeller frmSelectSeller = new SelectSeller();         

frmSelectSeller.Show(); this.Hide(); 

}  

FORM2: 

private void SelectBtn_Click(object sender, RoutedEventArgs e) 

{ 

DataRowView drv = (DataRowView)dataGridSeller.SelectedItem;         

clsCreateInvoice.S_ID = int.Parse(drv["B_ID"].ToString());         

clsCreateInvoice.S_Code = drv["B_Code"].ToString();         

clsCreateInvoice.S_Name_Address = drv["B_Name"].ToString() + " ," + drv["B_Address_1"].ToString() + " ," + drv["B_Address_2"].ToString(); 

CreateInvoice frmCreateInvoice = new CreateInvoice();         

frmCreateInvoice.txtSellerCode.Text = drv["B_Code"].ToString();         

frmCreateInvoice.lblSellerNameAddress.Text = drv["B_Name"].ToString() + " ," + drv["B_Address_1"].ToString() + " ," + drv["B_Address_2"].ToString();        

 frmCreateInvoice.Show(); 

this.Hide(); 

}