VB.NET How to add Event Handler to ComboBoxColumn located in programmatically created controls? - vb.net

Question

I've got part of my code that creates a tab in a tabcontrol, and then fills it with a datagridview which contains a couple columns that are DataGridViewComboBoxColumn.
It looks like this:
Private Sub NewTabPage()
Dim TabPageCount As Integer = RacerOrderTAB.TabPages.Count
RacerOrderTAB.TabPages.Add(TeamNames(TabPageCount)) 'teamnames() is an array of team names
Dim CurrentTabPage = RacerOrderTAB.TabPages(TabPageCount)
Dim GridToAdd As New DataGridView
GridToAdd.Size = CurrentTabPage.Size
GridToAdd.AutoSizeColumnsMode = DataGridViewAutoSizeColumnsMode.Fill
GridToAdd.Location = New Point(CurrentTabPage.Location.X, CurrentTabPage.Location.Y)
GridToAdd.Columns.Add("ShiftCOL", "Shift Name")
GridToAdd.Name = "grid_" & CurrentTabPage.Text
For y As Integer = 1 To ShiftSetup.racerspershift 'add extra column for each racer in shift
Dim cmb As New DataGridViewComboBoxColumn
cmb.HeaderText = "Racer" & y
cmb.Name = "Racer_" & y
cmb.MaxDropDownItems = AmountOfRacers
cmb.DisplayStyle = DataGridViewComboBoxDisplayStyle.DropDownButton
GridToAdd.Columns.Add(cmb)
Next
RacerOrderTAB.TabPages(TabPageCount).Controls.Add(GridToAdd)
End Sub
But I've been having difficulty in adding an eventhandler for the comboboxes. What I want to happen is that when a combobox is clicked and opened, I populate it with the items I want.
I managed to vaguely get it working by adding:
AddHandler GridToAdd.EditingControlShowing, AddressOf <sub name>
but then have been unable to figure out which combobox was clicked, and how to populate it. It's also been requiring like four clicks before the drop list will appear. I'm only slightly very confused.
Thanks for any advice; these DataGridViewComboBoxColumns [deep breath] have been confusing me a lot!

Answer 1

It may be a little hacky but it should do what you are asking… hopefully. I created two List(Of String) variables. AllRacers contains all the racers… i.e. all the names we want to appear in a combo box such that there is no other combo box on that row that has an item selected. These names are what all combo boxes on all rows would initially contain in the selectable items list.
The other List(Of String) UsedRacers contains a list of all the “comboboxes” on the current row that have selected items. Each time a cell value is changed and it is one of the “combobox” column cells, then UsedRacers is cleared/updated to reflect the added/changed selected item on the current row.
When a “comboBox” cell value is changed, SetUsedRacersForRow is called…
Private Sub SetUsedRacersForRow(rowIndex As Int16)
UsedRacers.Clear()
Dim curValue = ""
For i = 1 To racersPerShift
If (Not (dgvRacers.Rows(rowIndex).Cells(i).Value Is Nothing)) Then
curValue = dgvRacers.Rows(rowIndex).Cells(i).Value.ToString()
If (Not (String.IsNullOrEmpty(curValue))) Then
UsedRacers.Add(curValue)
End If
End If
Next
End Sub
The code above loops through all the “combobox” cells in the given row and if a “combobox” cell has something selected, the selected value is added to the UsedRacers list.
Now that the selected items for all the “comboboxes” in that row are in the UsedRacers list, we can now loop through each “combobox” cell in that row and set the proper list of names. To help, a method is created that returns a DataGridViewComboBoxCell such that the names in the current UsedRacers list will NOT be in the DataGridViewComboBoxCell’s list of selectable names.
The only issue here would be with cells that currently have an item selected. Each “combobox” cell with an item selected will uniquely need to have its selected item in its list of items. To remedy this, a check is needed to see if the “combobox” cell contains a value. If the “combobox” cell DOES contain a selected value, then this value is also contained in the UsedRacers list. Since THIS cell is the cell that is in the UseRacers list… then we need to ADD this value to this cells items list. Otherwise, we would not be able to display the unique selection.
To keep the UsedRacers list consistent, we need to add this item directly to the individual “combobox” cell and not remove or alter the UsedRacers list as this will be used for the other “combobox” cells. In other words… whatever value is selected in a combo box, we need to make sure it is one of the items in the “combobox’s” list of selectable items. I hope that makes sense.
This can all be done in the DataGridViews CellChanged event.
Private Sub dgvRacers_CellValueChanged(sender As Object, e As DataGridViewCellEventArgs) Handles dgvRacers.CellValueChanged
If (e.ColumnIndex >= 1 And e.ColumnIndex <= racersPerShift) Then
SetUsedRacersForRow(e.RowIndex)
For i = 1 To racersPerShift
Dim newCell As DataGridViewComboBoxCell = GetCurrentComboBoxCell()
If (Not (dgvRacers.Rows(e.RowIndex).Cells(i).Value Is Nothing)) Then
Dim curValue = dgvRacers.Rows(e.RowIndex).Cells(i).Value.ToString()
newCell.Items.Add(curValue)
newCell.Value = curValue
End If
dgvRacers.Rows(e.RowIndex).Cells(i) = newCell
Next
End If
End Sub
In the code above, a method GetCurrentComboBoxCell (below) returns a DataGridViewComboBoxCell such that the items in the combo boxes list of items does not contain any items that are in the UsedRacers list. Because of this, a check is needed (above) to see if the cell already contains a value. NOTE: the DataGridViewComboBoxCell returned will always contain a “blank” empty item. This is necessary to allow the user to “De-Select” any currently selected value and then make the “De-Selected” item available to the other combo box cells.
Public Function GetCurrentComboBoxCell() As DataGridViewComboBoxCell
Dim newComboCell = New DataGridViewComboBoxCell()
newComboCell.DisplayStyle = DataGridViewComboBoxDisplayStyle.DropDownButton
newComboCell.FlatStyle = FlatStyle.Flat
newComboCell.Items.Add("")
For Each curRacer In AllRacers
If (Not UsedRacers.Contains(curRacer)) Then
newComboCell.Items.Add(curRacer)
End If
Next
Return newComboCell
End Function
Finally, putting all this together…
Dim racersInShift = 3
Dim AllRacers As List(Of String) = New List(Of String) From {"John", "Bobby", "Trent", "Josh", "Chapman", "Henry", "George", "Marvin"}
'Dim racersPerShift As Int16 = AllRacers.Count '<-- should be MAX value
Dim racersPerShift As Int16 = 4
Dim UsedRacers = New List(Of String)
Private Sub Form2_Load(sender As Object, e As EventArgs) Handles MyBase.Load
BuildGrid()
End Sub
Private Sub BuildGrid()
dgvRacers.Size = New Size(800, 200)
dgvRacers.AutoSizeColumnsMode = DataGridViewAutoSizeColumnsMode.Fill
'dgvRacers.Location = New Point(50, 200)
dgvRacers.Columns.Add("ShiftCOL", "Shift Name")
dgvRacers.Name = "RacersDGV"
dgvRacers.EditMode = DataGridViewEditMode.EditOnEnter
dgvRacers.AllowUserToAddRows = False
AddRacerColumns()
AddRacerRows()
End Sub
Private Sub AddRacerColumns()
Dim newColumn As DataGridViewComboBoxColumn
For i As Integer = 1 To racersPerShift
newColumn = GetNewComboBoxColumn("Racer" & i, "Racer " & i)
dgvRacers.Columns.Add(newColumn)
Next
End Sub
Private Sub AddRacerRows()
For i As Integer = 1 To racersInShift
Dim row As New DataGridViewRow
dgvRacers.Rows.Add(row)
Next
End Sub
Private Sub dgvRacers_CellValueChanged(sender As Object, e As DataGridViewCellEventArgs)
‘See code above
End Sub
Private Sub SetUsedRacersForRow(rowIndex As Int16)
‘See code above
End Sub
Public Function GetCurrentComboBoxCell() As DataGridViewComboBoxCell
‘See code above
End Function
‘Lastly a method to set a whole `DataGridviewComboBoxColumn` which is used to initialize all the combo box columns
Public Function GetNewComboBoxColumn(colName As String, colHeader As String) As DataGridViewComboBoxColumn
Dim newComboCol = New DataGridViewComboBoxColumn()
newComboCol.DisplayStyle = DataGridViewComboBoxDisplayStyle.DropDownButton
newComboCol.FlatStyle = FlatStyle.Flat
newComboCol.Items.Add("")
newComboCol.HeaderText = colHeader
newComboCol.Name = colName
For Each curRacer In AllRacers
newComboCol.Items.Add(curRacer)
Next
Return newComboCol
End Function
I hope this helps, I am guessing there is an easier way to do this.