check if textbox exists vba (using name) - vba

Question

I am using Ms-Access and I created a userform which has a number of Textboxes on it. The boxes are named: Box1, Box2, Box3 ...
I need to loop through all boxes, but I don't know which is the last one. To avoid looping through all userform controls I thought of trying the following:
For i =1 To 20
If Me.Controls("Box" & i).value = MyCondition Then
'do stuff
End If
Next i
This errors at Box6, which is the first box not found. Is there a way to capture this error and exit the loop when it happens.
I know I could use On Error but I 'd rather capture this specific instance with code instead.
Thanks,
George

Answer 1

A Controls collection is a simplified collection of controls (obviously) and share a same order as a placement order of controls.
First of all, even a creatable collection object lacks methods such as Exists or Contains , hence you need a function with error handling to checking/pulling widget from a collection.
Public Function ExistsWidget(ByVal Name As String) As Boolean
On Error Resume Next
ExistsWidget = Not Me.Controls(Name) Is Nothing
On Error GoTo 0
End Function
If you really doesnt like "ask forgiveness not permission" option you can pull entire ordered collection of your textboxes (and/or check existance by name in another loop with similar logic).
Public Function PullBoxes() As Collection
Dim Control As MSForms.Control
Set PullBoxes = New Collection
For Each Control In Me.Controls
If TypeOf Control Is MSForms.TextBox And _
Left(Control.Name, 3) = "Box" Then
Call PullBoxes.Add(Control)
End If
Next
End Function
Since names of widgets are unique - you can return a Dictionary from that function with (Control.Name, Control) pairs inside and able to check existance of widget by name properly w/o an error suppression.
There's a good guide to Dictionary if it's a new information for you.
Anyway, no matter what object you choose, if user (or code) is unable to create more of thoose textboxes - you can convert this Function above to a Static Property Get or just to a Property Get with Static collection inside, so you iterate over all controls only once (e.g. on UserForm_Initialize event)!
Public Property Get Boxes() As Collection
Static PreservedBoxes As Collection
'There's no loop, but call to PullBoxes to reduce duplicate code in answer
If PreservedBoxes Is Nothing Then _
Set PreservedBoxes = PullBoxes
Set Boxes = PreservedBoxes
End Property
After all, the last created TextBox with name Box* will be:
Public Function LastCreatedBox() As MSForms.TextBox
Dim Boxes As Collection
Set Boxes = PullBoxes
With Boxes
If .Count <> 0 Then _
Set LastCreatedBox = Boxes(.Count)
End With
End Function
I think that now things are clearer to you! Cheers!
Note: All code are definitely a bunch of methods/properties of your form, hence all stuff should be placed inside of form module.

Answer 2

Long story short - you cannot do what you want with VBA.
However, there is a good way to go around it - make a boolean formula, that checks whether the object exists, using the On Error. Thus, your code will not be spoiled with it.
Function ControlExists(ControlName As String, FormCheck As Form) As Boolean
Dim strTest As String
On Error Resume Next
strTest = FormCheck(ControlName).Name
ControlExists = (Err.Number = 0)
End Function
Taken from here:http://www.tek-tips.com/viewthread.cfm?qid=1029435
To see the whole code working, check it like this:
Option Explicit
Sub TestMe()
Dim i As Long
For i = 1 To 20
If fnBlnExists("Label" & i, UserForm1) Then
Debug.Print UserForm1.Controls(CStr("Label" & i)).Name & " EXISTS"
Else
Debug.Print "Does Not exist!"
End If
Next i
End Sub
Public Function fnBlnExists(ControlName As String, ByRef FormCheck As UserForm) As Boolean
Dim strTest As String
On Error Resume Next
strTest = FormCheck(ControlName).Name
fnBlnExists = (Err.Number = 0)
End Function

Answer 3

I would suggest testing the existence in another procedure per below: -
Private Sub Command1_Click()
Dim i As Long
i = 1
Do Until Not BoxExists(i)
If Me.Conrtols("Box" & i).Value = MyCondition Then
'Do stuff
End If
i = i + 1
Next
End Sub
Private Function BoxExists(ByVal LngID As Long) As Boolean
Dim Ctrl As Control
On Error GoTo ErrorHandle
Set Ctrl = Me.Controls("BoX" & LngID)
Set Ctrl = Nothing
BoxExists = True
Exit Function
ErrorHandle:
Err.Clear
End Function
In the above, BoxExists only returns true if the box does exists.

Answer 4

You have taken an incorrect approach here.
If you want to limit the loop, you can loop only in the section your controls reside e.g. Detail. You can use the ControlType property to limit controls to TextBox.
Dim ctl As Control
For Each ctl In Me.Detail.Controls
If ctl.ControlType = acTextBox Then
If ctl.Value = MyCondition Then
'do stuff
End If
End If
Next ctl
I believe the loop will be faster than checking if the control name exists through a helper function and an On Error Resume Next.
But this only a personal opinion.