while clicking down arrow cursor need to come other control - vb.net

Question

i given code like this:
Private Sub txtemployeename_KeyDown(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyEventArgs) Handles txtemployeename.KeyDown
keyval = e.KeyData
Dim keyData As System.Windows.Forms.Keys = e.KeyData
If keyData = Keys.Down Then
LstEmployee.Visible = True
LstEmployee.Focus()
End If
End Sub
while i am cliking down arrow first time that is not focusing to listbox,second time am clicking down arrow that is focusing..also once cursor come to tha list box,if i clik enter that should be displayed in text box..for that i given code like this..
Private Sub LstEmployee_Enter(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles LstEmployee.Enter
txtemployeename.Text = LstEmployee.SelectedItem
End Sub
but this is not working properly..for loading list box i given code like this:
Private Sub txtemployeename_KeyPress(ByVal sender As System.Object, ByVal e As System.Windows.Forms.KeyPressEventArgs) Handles txtemployeename.KeyPress
Dim s As String = txtemployeename.Text
LstEmployee.Visible = True
loadlistbox(LstEmployee, "select Ename from EmployeeMaster_tbl where Ename LIKE'%" & s & "%' ")
End Sub

Answer 1

You should rely on the KeyUp event rather than on the KeyDown one. Also for the ListBox you just need the SelectedIndexChanged event. Additionally, your code has quite a few errors (wrong query (-> you don't need to call your DB every time to order the items in the ListBox), relies on SelectedIndex rather than on SelectedItem...). Here you have an updated version:
Private Sub txtemployeename_KeyUp(sender As Object, e As System.Windows.Forms.KeyEventArgs) Handles txtemployeename.KeyUp
Dim s As String = txtemployeename.Text
LstEmployee.Visible = True
Dim list = LstEmployee.Items.Cast(Of String)()
Dim query = From item As String In list Where item.Length >= s.Length AndAlso item.ToLower().Substring(0, s.Length) = s.ToLower() Select item
If (query.Count > 0) Then
Dim newItems = New List(Of String)()
For Each result In query
newItems.Add(result)
Next
LstEmployee.Items.Clear()
For Each newItem In newItems
LstEmployee.Items.Add(newItem)
Next
End If
End Sub
Private Sub LstEmployee_SelectedIndexChanged(sender As System.Object, e As System.EventArgs) Handles LstEmployee.SelectedIndexChanged
txtemployeename.Text = LstEmployee.SelectedItem
End Sub
The code above checks for occurrences (i.e., if the whole string in the txtemployeename matches (caps do not matter) the starting substring of, at least, one element in LstEmployee) every time a new character is introduced in txtemployeename. The ListBox is updated with these ocurrences. txtemployeename displays the name of the selected item in LstEmployee.
I hope that this will be enough to help you to build the code required to deliver the exact functionalities you are after.
NOTE: bear in mind that this approach (deleting/adding Items) is incompatible with cases where the ListView is populated with a DataSource. If you rely on a DataSource you would have to update this code accordingly.
NOTE2: the proposed approach deals with the elements in the ListView. You have to introduce these elements at the start from whatever source you are using; this code only updates existing information (items in the ListBox). Also bear in mind that this code is expected to be corrected to match your exact requirements; for example: list has to be associated with the total number of items (the ones retrieved from your datasource at the start), not with the current ones (as displayed in the code; it just represents a simplified version of the problem): every time a new population occurs all the items (other than the target ones) are deleted and thus the ListBox does not represent a reliable source. Example to understand this: at the start, you have "aaaa", "bbbb", "cccc"; if you type "a", all the elements except "aaaa" would be deleted. If you type now "b" and consider the actual elements in the ListBox, no change would occur as far as the only element is "aaaa"; you would have to consider all the original elements (which, as suggested via comment, might be stored at the start in an array/list of strings).