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With ListView, how to make sure one element is always selected?

Posted on 2008-06-17
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Last Modified: 2010-04-21
I have created a listview control, which works OK, except that I want to make sure that one element is always selected - i.e that it never happens that no element is selected.

My problem is that if the user clicks in the listview outside of the populated rows, the previously selected element is deselected. When this happens, I would prefer the last element to be selected.  When loading my form I want the first element to be selected. I have the same problem with both the "Click" event and the "SelectedIndexChanged" event. Neither are activated when clicking in the listview outside of the populated rows, yet an existing selection is cleared.

Key properties I have assigned to my listview: MultiSelect = false, HideSelection = False, and FullRowSelect = True
Private Sub ShowLinkList()
 
        ' If no companies are defined, display a dummy element, otherwise display the real links
 
        ' ----- So, read the table of links which have been defined ----
        ' Create a connection string 
        Dim connString As String = "Provider=VFPOLEDB.1;" + _
               "Data Source=" & MyDataPath & ";"
        Dim myConnection As OleDbConnection = New OleDbConnection
        Dim strSqlQuery As String
        myConnection.ConnectionString = connString
        ' Create a data adapter
        strSqlQuery = "SELECT * FROM TaInit WHERE s200name <> '' ORDER BY TempaidID"
        Dim da As OleDbDataAdapter = New OleDbDataAdapter(strSqlQuery, myConnection)
        ' Create a new dataset 
        Dim ds As DataSet = New DataSet
        ' Fill dataset 
        da.Fill(ds, "TaInit")
 
        '--- Display the three columns ---
        ' Can also change the width of the columns by changing the '100' to a different value. 
        ' The alignment can also be changed, to be right or centre aligned.
        lvwCompanyLinks.Columns.Add("Co ID", 80, HorizontalAlignment.Left)
        lvwCompanyLinks.Columns.Add("Company Name", 150, HorizontalAlignment.Left)
        lvwCompanyLinks.Columns.Add("Target Company", 220, HorizontalAlignment.Left)
        lvwCompanyLinks.MultiSelect = False
 
        '--- Populate the rows -----
        ' Define variable to hold the ListItem information 
        ' so that we can add values to the column we want to change 
        Dim lSingleItem As ListViewItem
        ' Check if any links have been defined
        With ds.Tables(0)
            If .Rows.Count = 0 Then
                ' Indicate that we have NO links
                bLinksDefined = False
 
                ' Create dummy link as no links are defined
                lSingleItem = lvwCompanyLinks.Items.Add("TBA")     ' Create a new line, and assign the ListItem into the variable so we can add sub items
                lSingleItem.SubItems.Add("TBA")     ' The first sub item for the first line
                lSingleItem.SubItems.Add("TBA")     ' The second sub item for the first line
 
            Else
                ' Indicate that we DO have links
                bLinksDefined = True
 
                Dim i As Integer                    ' Row counter
                For i = 0 To .Rows.Count - 1
                    ' Display the list of real links
                    lSingleItem = lvwCompanyLinks.Items.Add(.Rows(i).Item("TempaidID"))  'Create a new line, and assign the ListItem into the variable so we can add sub items
                    'The first sub item for the line
                    lSingleItem.SubItems.Add(.Rows(i).Item("TaName"))
                    'The second sub item for the line
                    lSingleItem.SubItems.Add(.Rows(i).Item("S200Name"))
                Next
            End If
 
        End With
 
        ' No item is selected. Check if there is a row to select!
        lvwCompanyLinks.Items(0).Selected = True
        lvwCompanyLinks.Items(0).Focused = True
        lvwCompanyLinks.Focus()
 
    End Sub
 
    Private Sub lvwCompanyLinks_SelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles lvwCompanyLinks.SelectedIndexChanged
 
        ' NOTE To show that a row is selected, even when the control does not have focus, 
        '   set HideSelection = False, and FullRowSelect = True.
 
        ' Check if a row is selected
        If lvwCompanyLinks.SelectedIndices.Count = 0 Then Exit Sub
 
        Dim lvi As ListViewItem = lvwCompanyLinks.SelectedItems(0)
        MessageBox.Show(lvi.Text & " / " & lvi.SubItems(1).Text & " has been selected.")
 
    End Sub

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Question by:logicalc
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6 Comments
 
LVL 48

Expert Comment

by:jpaulino
ID: 21811575
When you select a new item it fires two times the event: unselect the previous item and select the new one.

This way you have to check if you do one or other action. You can do that this way:

Private Sub SelectedIndexChanged(...) Handles Listview1.SelectedIndexChanged

If Me.ListView1.SelectedItems.Count > 0 Then
  Debug.WriteLine(Me.ListView1.SelectedItems(0).Text)
End If

End Sub
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Author Comment

by:logicalc
ID: 21811792
Thanks jpaulino, but the problem is not that I cannot recognise when an item _is_ selected, but that I cannot recognise when _nothing_ is selected.

Because SelectedIndexChanged is also called when the previous item is unselected, I cannot use this to find if nothing has been selected.
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LVL 48

Expert Comment

by:jpaulino
ID: 21812015
Sorry but I didn't looked very well to the code!

The best solution (I think) is to show a message to the user to select any item but you can do this walkaround using a timer to detect if there's no item selected and force the selection.


    Dim tm As New Timer
    Dim lastItem As Integer
 
    Sub tmSelectItem()
        tm.Stop()
        If Me.ListView1.SelectedItems.Count = 0 Then
            Me.ListView1.Items(lastItem).Selected = True
        End If
    End Sub
 
 
    Private Sub ListView1_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ListView1.SelectedIndexChanged
        If Me.ListView1.SelectedItems.Count > 0 Then
            If Me.ListView1.SelectedItems(0).Index <> lastItem Then
                lastItem = Me.ListView1.SelectedItems(0).Index
                MsgBox(Me.ListView1.SelectedItems(0).Text)
            End If
        Else
            tm.Interval = 50
            AddHandler tm.Tick, AddressOf tmSelectItem
            tm.Start()
        End If
    End Sub

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Author Comment

by:logicalc
ID: 21876172
Thanks jpaulino, this certainly does ensure an item is selected.

But what I really wanted is to force the user to actually make a choice, so that when the user presses a button or selects a menu I know that he has deliberately selected an option. Otherwise I need to check whether an item has been selected and abort if not - or disable all the controls - and ether method makes a lot of unnecsssary work.

Would a different control be better?
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LVL 48

Accepted Solution

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jpaulino earned 500 total points
ID: 21879590
>> Otherwise I need to check whether an item has been selected and abort if not - or disable all the controls - and ether method makes a lot of unnecsssary work.

But this is the normal procedure. Check it any item is selected and show a waning message to the user.

You can use other controls, like a datagridview, that keeps always a selected row, but you will also spend some time to implementing.
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Author Closing Comment

by:logicalc
ID: 31468100
Thanks for your help
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