Question

I am trying to add a combo box to a user form which will be created at run time , the problem I am facing is to add items to the combo box? Not able to figure out where the mistake would be. Thanks.

    Function addComboBox(ByRef TempForm As Object, ByVal controlType As String, 
ByVal pos As Integer, ByVal strCaption As String, ByVal strValues As String)

     Dim NewComboBox As MSforms.ComboBox
     Dim arr As Variant
     Dim i As Integer

     Set NewComboBox = TempForm.Designer.Controls.Add("forms.ComboBox.1")
      arr = Split(strValues, ";")


        With NewComboBox
                .Name = strCaption & "_" & controlType & "_" & pos
                .Top = 20 + (12 * pos)
                .Left = 100
                .Width = 150
                .Height = 12

        End With



      For i = 0 To UBound(arr)

       NewComboBox.AddItem arr(i)

      Next i

    End Function

Answer 1

Remove the word Designer

Try this (Tried And Tested)

Set NewComboBox = TempForm.Controls.Add("Forms.ComboBox.1")

FOLLOWUP

Try this. (TRIED AND TESTED)

Option Explicit

Sub Sample()
    Dim TempForm As Object
    Dim Ret

    Set TempForm = ThisWorkbook.VBProject.VBComponents.Add(3)

    Ret = addComboBox(TempForm, "CBox", 1, "MyCombo", "1;2;3;4")

    VBA.UserForms.Add(TempForm.Name).Show
End Sub

Function addComboBox(ByRef TempForm As Object, ByVal controlType As String, _
ByVal pos As Integer, ByVal strCaption As String, ByVal strValues As String)

    Dim NewComboBox As MSForms.ComboBox
    Dim n As Long, nLines As Long, i As Long
    Dim arr As Variant

    Set NewComboBox = TempForm.designer.Controls.Add("Forms.ComboBox.1")
    arr = Split(strValues, ";")


    With NewComboBox
        .Name = strCaption & "_" & controlType & "_" & pos
        .Top = 20 + (12 * pos)
        .Left = 10
        .Width = 150
        .Height = 12
    End With

    n = 2

    With TempForm
        nLines = .CodeModule.CountOfLines
        .CodeModule.InsertLines nLines + 1, "Private Sub UserForm_Initialize()"
        For i = 0 To UBound(arr)
            .CodeModule.InsertLines nLines + n, "    " & _
            NewComboBox.Name & ".AddItem " & arr(i)
            n = n + 1
        Next i
        .CodeModule.InsertLines nLines + n, "End Sub"
    End With
End Function

SCREENSHOT

MORE FOLLOWUP

Thanks for the solution , In case if I have to call addComboBox more than once, i.e to add two or more combo boxes , UserForm_Initialize sub will be created more than once, which is problem again. – Vikram

In such a scenario you have to check if the UserForm_Initialize proc exists and then parse it. See the code below. I have added a new optional parameter S to your function. I am using that to place the combos one below the other.

Option Explicit

Sub Sample()
    Dim TempForm As Object
    Dim Ret

    Set TempForm = ThisWorkbook.VBProject.VBComponents.Add(3)

    Ret = addComboBox(TempForm, "CBox", 1, "MyCombo", "1;2;3;4")

    Ret = addComboBox(TempForm, "CBox1", 1, "MyCombo1", "5;6;7;8", 20)

    Ret = addComboBox(TempForm, "CBox2", 1, "MyCombo2", "9;10;11;12", 40)

    VBA.UserForms.Add(TempForm.Name).Show
End Sub

Function addComboBox(ByRef TempForm As Object, ByVal controlType As String, _
ByVal pos As Integer, ByVal strCaption As String, ByVal strValues As String, _
Optional s As Long)

    Dim NewComboBox As MSForms.ComboBox
    Dim n As Long, nLines As Long, i As Long, uInitLine As Long
    Dim arr As Variant
    Dim MyModule As Object

    Set NewComboBox = TempForm.Designer.Controls.Add("Forms.ComboBox.1")
    arr = Split(strValues, ";")

    With NewComboBox
        .Name = strCaption & "_" & controlType & "_" & pos
        .Top = 20 + (12 * pos) + s
        .Left = 10
        .Width = 150
        .Height = 12
    End With

    '~~> Connect to the code module of the Userform
    Set MyModule = ThisWorkbook.VBProject.VBComponents(TempForm.Name).CodeModule

    '~~> Check if there is a procedure called UserForm_Initialize
    On Error Resume Next
    uInitLine = MyModule.ProcStartLine("UserForm_Initialize", 0)
    On Error GoTo 0

    With TempForm
        '~~> UserForm_Initialize Found
        If uInitLine > 0 Then
            nLines = uInitLine + 2: n = 0
            For i = 0 To UBound(arr)
                .CodeModule.InsertLines nLines + n, "    " & _
                NewComboBox.Name & ".AddItem " & arr(i)
                n = n + 1
            Next i
        Else
            n = 2

            nLines = .CodeModule.CountOfLines

            .CodeModule.InsertLines nLines + 1, "Private Sub UserForm_Initialize()"
            For i = 0 To UBound(arr)
                .CodeModule.InsertLines nLines + n, "    " & _
                NewComboBox.Name & ".AddItem " & arr(i)
                n = n + 1
            Next i
            .CodeModule.InsertLines nLines + n, "End Sub"
        End If
    End With
End Function

SCREENSHOT (Of Userform)

SCREENSHOT (Of Userform Code)