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Updating RadListControl items issue

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Christian asked on 27 Sep 2014, 04:28 PM

( First of all I need to clarify that I could manage both C# or VB solution to solve this issue )

I have a RadListControl where I would like to use it to list the runing processes in the system (with a condition that no more than 1 process with the same name),
that thing is done and I'm trying to update the list each 2 seconds (firstly determining If exists changes to update the current list),
I'm saving the SelectedItems property of the control to restore the selected items in the RadListControl after updating the list and here is the problem, after clearing the items of the control using the Items.Clear method the Scrollbar moves up to the top of the control and I need to scrolldown to the desired position again and again.

I would like to keep the current position after updating the items in the control, just like Windows TaskManager does for example.

I also tried to set a collection of RadDataItem as the control DataSource, but then the Image property for each item is empty (I don't know why).

I attached a gif in this post that demonstrates the problem,
As you can see in the Gif, when I run a new process (the window which is at the left border of the gif) the process list is moved to top, and the same thing happens when I close that process.

I don't know what more to try, here is the relevant part of the code:

Private Sub Timer_RefreshProcessList_Tick(ByVal sender As Object, ByVal e As EventArgs) _
Handles Timer_RefreshProcessList.Tick
    ' Processes that shouldn't be listed.
    Dim BlackListedProcesses As String() =
    ' Get the runing processes.
    Dim Processes As Process() = Process.GetProcesses
    ' Filter the processes by its name
    ' then set the RadListDataItem items containing the names and the process icons.
    Dim ProcessItems As IEnumerable(Of RadListDataItem) =
        (From proc As Process In Processes
        Where Not BlackListedProcesses.Contains(proc.ProcessName)
        Order By proc.ProcessName Ascending).
        GroupBy(Function(proc As Process) proc.ProcessName).
        Select(Function(procs As IGrouping(Of String, Process))
                   If Not procs.First.HasExited Then
                           Return New RadListDataItem With
                                    .Active = False,
                                    .Text = String.Format("{0}.exe", procs.First.ProcessName),
                                    .Image = ResizeImage(Icon.ExtractAssociatedIcon(procs.First.MainModule.FileName).ToBitmap,
                                                         Width:=16, Height:=16)
                       Catch ex As Exception
                           Return Nothing
                       End Try
                       Return Nothing
                   End If
               End Function)
    ' If the RadListControl does not contain any item then...
    If Me.RadListControl_ProcessList.Items.Count = 0 Then
        With Me.RadListControl_ProcessList
            .Items.AddRange(ProcessItems) ' Add the RadListDataItems for first time.
        End With
        Exit Sub
    End If
    ' If RadListDataItems count is not equal than the runing process list count then...
    If Me.RadListControl_ProcessList.Items.Count <> ProcessItems.Count Then
        ' Save the current selected items.
        Dim SelectedItems As IEnumerable(Of String) =
            From Item As RadListDataItem
            In Me.RadListControl_ProcessList.SelectedItems
            Select Item.Text
        ' For Each ctrl As RadListDataItem In ProcessItems
        '     ctrl.Dispose()
        ' Next
        With Me.RadListControl_ProcessList
            ' .AutoScroll = False
            ' .SuspendSelectionEvents = True
            ' .SuspendItemsChangeEvents = True
            ' .SuspendLayout()
            ' .BeginUpdate()
            .Items.Clear() ' Clear the current RadListDataItems
            .Items.AddRange(ProcessItems) ' Add the new RadListDataItems.
            ' .EndUpdate()
            ' .ResumeLayout()
        End With
        ' Restore the selected item(s).
        For Each Item As RadListDataItem In Me.RadListControl_ProcessList.Items
            If SelectedItems.Contains(Item.Text) Then
                Item.Selected = True
                Item.Active = True
                With Me.RadListControl_ProcessList
                    ' .ScrollToItem(Item)
                    ' .ListElement.ScrollToItem(Item)
                    ' .ListElement.ScrollToActiveItem()
                End With
            End If
        Next Item
        With Me.RadListControl_ProcessList
            ' .AutoScroll = True
            ' .SuspendSelectionEvents = False
            ' .SuspendItemsChangeEvents = False
        End With
    End If
End Sub

Thanks in advance.


What I did time ago to solve this issue with a normal ListBox control is this (I can't reproduce it in a RadListControl):

' [ListBox] Select item without jump
' Original author of code is "King King"
' Url:
' Examples :
' Select_Item_Without_Jump(ListBox1, 50, ListBoxItemSelected.Select)
' For x As Integer = 0 To ListBox1.Items.Count - 1
'    Select_Item_Without_Jump(ListBox1, x, ListBoxItemSelected.Select)
' Next
''' <summary>
''' Indicates whether the ListBox Item should be Selected or Unselected.
''' </summary>
Private Enum ListBoxItemSelected
    ''' <summary>
    ''' Indicate that ListBox Item should be Selected.
    ''' </summary>
    [Select] = 1
    ''' <summary>
    ''' Indicate that ListBox Item should be Unselected.
    ''' </summary>
    [Unselect] = 0
End Enum
''' <summary>
''' Selects or unselects a ListBox Item without jumping to the Item location on the layout.
''' </summary>
Public Shared Sub Select_Item_Without_Jump(lb As ListBox, index As Integer, selected As ListBoxItemSelected)
    Dim i As Integer = lb.TopIndex ' Store the selected item index
    lb.BeginUpdate() ' Disable drawing on control
    lb.SetSelected(index, selected) ' Select the item
    lb.TopIndex = i ' Jump to the previous selected item
    lb.EndUpdate() ' Eenable drawing
End Sub

1 Answer, 1 is accepted

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Telerik team
answered on 01 Oct 2014, 01:33 PM
Hello Christian,

Thank you for contacting us.

If I understand correctly you want to preserve the scrollbar value along with the selected item, which can be done as follows:
Private Sub radButton1_Click(sender As Object, e As EventArgs)
    Dim scrollValue As Integer = radListControl1.ListElement.VScrollBar.Value
    Dim selectedIndex As Integer = radListControl1.SelectedIndex
    'reset the items
    radListControl1.ListElement.VScrollBar.Value = scrollValue
    radListControl1.SelectedIndex = selectedIndex
End Sub

I hope this helps.

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