Search button losing datada - winforms

Question

Afternoon,
I have a search button which searches the list of the users is either by IDnumber,Username or department.
I have 2 list view which the users clicks and it load the selected user to the second list view. now the problem is after u clicked users from listview1 and u went to type ID,Username or select department and click search...It clears all the users you selected and bring new users u where searching.
I want to be able to select the users and be able to search without losing my current selected users from the listview
my code ;
//search button
private void Searchbutton_Click(object sender, EventArgs e)
{
try
{
listView1.Items.Clear();
string sID = string.IsNullOrEmpty(txtUserID.Text) ? null : txtUserID.Text;
string sDepartment;
if (cboDepartment.SelectedItem != null)
{
sDepartment = cboDepartment.SelectedItem.ToString();
}
else
{
sDepartment = "";
}
oConnection = new SqlConnection(_connectionString);
oCommand = new SqlCommand(#"Select us.sFieldValue5, u.sUserName, d.sName, TB_USER_CUSTOMINFO.sFieldValue2
From TB_USER u(nolock)
left join [TB_USER_CUSTOMINFO] us(nolock) on us.nUserIdn = u.nUserIdn
left join TB_USER_CUSTOMINFO on u.nUserIdn = TB_USER_CUSTOMINFO.nUserIdn
left join TB_USER_DEPT d(nolock) on d.nDepartmentIdn = u.nDepartmentIdn
where u.sUserName like '%'+ISNULL(#UserName,u.sUserName)+'%'
and us.sFieldValue5 = isnull(#IDNumber,us.sFieldValue5)
and d.sDepartment like '%'+isnull(#Department,d.sDepartment)+'%'", oConnection);
oCommand.Parameters.AddWithValue("UserName", string.IsNullOrEmpty(txtUsername.Text) ? DBNull.Value : (object)txtUsername.Text);
oCommand.Parameters.AddWithValue("IDNumber", string.IsNullOrEmpty(txtUserID.Text) ? DBNull.Value : (object)txtUserID.Text);
oCommand.Parameters.AddWithValue("Department", string.IsNullOrEmpty(sDepartment) ? DBNull.Value : (object)sDepartment);
oConnection.Open();
oDataset = new System.Data.DataSet();
SqlDataReader oReader = oCommand.ExecuteReader();
while (oReader.Read())
{
ListViewItem item1 = new ListViewItem(oReader[1].ToString());
item1.SubItems.Add(oReader[2].ToString());
item1.SubItems.Add(oReader[3].ToString());
item1.SubItems.Add(oReader[0].ToString());
listView1.Items.AddRange(new ListViewItem[] {item1});
}
oReader.Close();
oConnection.Close();
}
//selected users
private void listView1_ItemChecked(object sender, ItemCheckedEventArgs e)
{
if (e.Item.Checked == true)
{
ListViewItem l = listView1.Items[e.Item.Index];
int i = l.SubItems.Count;
string sValue1 = l.SubItems[1].Text;
string sValue2 = l.SubItems[2].Text;
string sValue3 = l.SubItems[3].Text;
ListViewItem item1 = new ListViewItem(l.SubItems[0].Text.ToString());
item1.SubItems.Add(sValue3);
item1.SubItems.Add(sValue2);
item1.SubItems.Add(sValue1);
listView2.Items.AddRange(new ListViewItem[] { (ListViewItem)l.Clone() });
}
else if (e.Item.Checked == false)
{
ListViewItem l = listView1.Items[e.Item.Index];
foreach (ListViewItem i in listView2.Items)
{
if (i.SubItems[0].Text == l.SubItems[0].Text.ToString())
{
listView2.Items.Remove(i);
}
}
}
}

Answer 1

ListView remember which ListViewItems were checked. As soon as you say Items.Clear(), all that knowledge is lost.
To solve your problem, you will need to remember which users were checked, do your refresh, then go through and mark each user as checked again.
To do those steps, you really need to separate your model from your view. Create a User model object to hold the actual data, then populate your ListView with data from your model. When the user does another search, update or refresh your model objects, then rebuild your view.
Doing this model/view separation is a little more work up front, but future generations of maintenance programmers will bless your name.
BTW, ObjectListView -- an open source wrapper around a .NET ListView -- makes creating a fully functional ListView from a list of model objects trivially easy.