Move item in listbox up or down

[Lanc1988]

I have a listbox in which users can add items to it.. i would like to have a button that lets them move the selected item either up or down.

 

I called my checkedlistbox "listboxMiscGoals"

[snarfblam]

Assuming you are using vb...

 

    Sub MoveSelectedItemUp(ByVal Box As ListBox)

        Dim Index As Integer = Box.SelectedIndex    'Index of selected item

        Dim Swap As Object = Box.SelectedItem       'Selected Item

        If Not (Swap Is Nothing) Then               'If something is selected...

            Box.Items.RemoveAt(Index)                   'Remove it

            Box.Items.Insert(Index - 1, Swap)           'Add it back in one spot up

            Box.SelectedItem = Swap                     'Keep this item selected

        End If

    End Sub

[/Code]

 

If you are c# then... this is PROBABLY WRONG but you can get the jist of it

[Code]
void MoveSelectedItemUp(ListBox Box) {
int Index = Box.SelectedIndex; //Selected Index
object Swap = Box.SelectedItem; //Selected Item
If (Index == -1) { //If something is selected...
Box.Items.RemoveAt(Index); //Remove it
Box.Items.Insert(Index - 1, Swap); //Add it back in one spot up
Box.SelectedItem = Swap; //Keep this item selected
}
}
[/Code]

[Lanc1988]

yeah, i needed the vb one, thanks :)

[Lanc1988]

im having a problem when its already at the top and they click to move it up.. i stopped the error from happening, but it is completely removing the goal.

 

I tried adding Try, Catch, and End Try, but i dont know what to put under Catch to make it insert the item in the first place.

[snarfblam]

Ideally if the selected item is already at the top you want to disable the "move up" button since it cant be moved up. If you prefer not to, then replace the line "If Not (Swap Is Nothing) Then" with "If Index > 0 Then". This will only move items with an index 1 or higher (i.e. the second or higher item on the list).

[Lanc1988]

ok, when i replaced it with If Index > 0 Then it works fine for the move up, but what would i replace the If Not (Swap is nothing) part with for my move down button?

[snarfblam]

Just as the "Index > 0" condition tests if the selected item's index is greater than that of the first item, the move down function should test if the selected index is less than that of the last item. Keep in mind that you also need to either test if the index = -1 or if Swap is Nothing, either of which will indicate that nothing is selected. So... here. Have some code.

 

   Sub MoveSelectedItemDown(ByVal Box As ListBox)
       Dim Index As Integer = Box.SelectedIndex    'Index of selected item
       Dim Swap As Object = Box.SelectedItem       'Selected Item
       If (Index <> -1) AndAlso (Index + 1 < Box.Items.Count) Then
           Box.Items.RemoveAt(Index)                   'Remove it
           Box.Items.Insert(Index + 1, Swap)           'Add it back in one spot up
           Box.SelectedItem = Swap                     'Keep this item selected
       End If
   End Sub

[janblo]

I've actually created an ordered listbox in C# here : http://blogs.gaiaware.net/post/Building-an-Ordered-Ajax-ListControl-in-Gaia-Ajax-using-C.aspx

 

I've also used Gaia Ajax to automatically ajax-ify the listbox so that no full postback occurs.

[Armaggoth]

This implementation does it all on a single for loop, it's controlled by the index parameter, it must be -1 to move the item up (the index decreases) or 1 to move the item down (the index increases). It also works on a multiple selection listbox. The loop dynamically adjusts its direction depending on the index parameter:

 

private void MoveListboxItem(int index, ListBox listBox)
       {
           if (listBox.SelectedIndex != -1) //is there an item selected?
           {
//if it's moving up, the loop moves from first to last, otherwise, it moves from last to first
               for (int i = (index < 0 ? 0 : listBox.Items.Count - 1); index < 0 ? i < listBox.Items.Count : i > -1; i -= index)
               {
                   if (listBox.Items[i].Selected)
                   {
                      //if it's moving up, it should not be the first item, or, if it's moving down, it should not be the last
                       if ((index < 0 && i > 0) || (index > 0 && i < listBox.Items.Count - 1))
                       {
                        //if it's moving up, the previous item should not be selected, or, if it's moving down, the following item should not be selected
                           if ((index < 0 && !listBox.Items[i - 1].Selected) || (index > 0 && !listBox.Items[i + 1].Selected))
                           {
                               ListItem itemA = listBox.Items[i]; //the selected item

                               listBox.Items.Remove(itemA); //is removed

                               listBox.Items.Insert(i + index, itemA);//and swapped
                           }
                       }
                   }
               }
           }
       }

Edited February 24, 2010 by snarfblam