Looping through all Combo boxes on a VB form - vb.net

Question

I am making a grade application for a school project and I am wondering how I can loop through and check a value in all combo boxes on a certain form, I have 19 units to check; trying to be efficient without making 19 case statements. I have tried an array and me.controls.

Answer 1

Try this :
For Each c As Control In Me.Controls.OfType(Of ComboBox)()
'You cann acces to ComboBox her by c
Next

Answer 2

Note that if you have controls host by containers (TabControl, SPlitPanel, etc.) you may not find all of your controls.
Here is a recursive call that should return all of your controls:
Sub GetControlList(container As Control, ByVal ctlList As List(Of Control))
For Each child As Control In container.Controls
ctlList.Add(child)
If (child.HasChildren) Then
GetControlList(child, ctlList)
End If
Next
End Sub
I have on occasion had problems with the controls on SplitContainer panels so if you use a splitter make sure you are getting all your controls.
Once you have a complete list of controls you can operate on them. This sample is working with DataGridView controls:
Dim ctrls As New List(Of Control)
GetControlList(Me, ctrls)
For Each dgv As DataGridView In ctrls.OfType(Of DataGridView)()
AddHandler dgv.DataError, AddressOf DataGridView_DataError
Debug.Print(dgv.Name)
Next
FYI the generic data error code:
Private Sub DataGridView_DataError(sender As Object, e As DataGridViewDataErrorEventArgs)
Dim dgv As DataGridView = sender
Dim sGridName As String = dgv.Name.Replace("DataGridView", "")
Dim col As DataGridViewColumn = dgv.Columns(e.ColumnIndex)
Dim sColName As String = col.HeaderText
MsgBox(sGridName & vbNewLine & "Column " & sColName & vbNewLine & e.Exception.Message, MsgBoxStyle.Exclamation)
End Sub

Answer 3

You already have the OfType(OF T) method. You use it like this:
ForEach box As ComboBox In MyForm.Controls.OfType(Of ComboBox)()
Next
But this only checks the direct children of your control. If you have container controls like GroupBox, Panels, FlowControlLayoutPanel, etc, you'll miss the controls nested inside them. But we can build a new OfType() method to search these recursively:
Public Module ControlExtensions
<Extension()>
Public Iterator Function OfTypeRecursive(Of T As Control)(ByVal Controls As ControlCollection) As IEnumerable(Of T)
For Each parent As Control In Controls
If parent.HasChildren Then
For Each child As Control In OfTypeRecursive(Of T)(parent.Controls)
Yield child
Next child
End If
Next parent
For Each item As Control In Controls.OfType(Of T)()
Yield item
Next item
End Function
End Module
And you use it the same way:
ForEach box As ComboBox In MyForm.Controls.OfTypeRecursive(Of ComboBox)()
Next

Answer 4

You'll probably want to check containers for controls of the type you're looking for, here's a little function that should do the trick for you.
Private Function GetControls(Of T)(container As Control, searchChildren As Boolean) As T()
Dim Controls As New List(Of T)
For Each Child As Control In container.Controls
If TypeOf Child Is T Then
DirectCast(Controls, IList).Add(Child)
End If
If searchChildren AndAlso Child.HasChildren Then
Controls.AddRange(GetControls(Of T)(Child, True))
End If
Next
Return Controls.ToArray()
End Function
Here's the usage, if search children is True then all child containers will be searched for the control you're looking for. Also, for the top most container we'll just pass in Me assuming you're calling the code from within your Form, otherwise you could pass the Form instance or a specific Panel, GroupBox, etc.
Dim ComboBoxes As ComboBox() = GetControls(Of ComboBox)(Me, True)