private void AddVendor()
 {
     AddModifyVendorWindow amvw = new AddModifyVendorWindow(null);
     amvw.Show();
     this.Close();
 }
 private void ModifyVendor()
 {
     AddModifyVendorWindow amvw = new AddModifyVendorWindow((List<Vendor>)vendorViewSource.Source);
     amvw.Show();
     this.Close();
 }