Change the drop-down width of a Combo Box

This tip shows you how to get and set the width of the drop down portion of a combo box. It also includes code to automatically set the drop down width based on the contents of a combo box by measuring the size of the text in each combo box item.

Start a new project and add a module. Then add the following code to the module:

' These functions required to set the drop-down width: 
Private Declare Function SendMessageLong Lib "user32" _
       Alias "SendMessageA" _
       (ByVal hwnd As Long, ByVal wMsg As Long, _
       ByVal wParam As Long, ByVal lParam As Long) As Long 
Private Const CB_GETDROPPEDWIDTH = &H15F 
Private Const CB_SETDROPPEDWIDTH = &H160 

' These are only required if you want to automatically 
' calculate the drop-down width: 
Private Type RECT 
    Left As Long 
    Top As Long 
    Right As Long 
    Bottom As Long 
End Type 
Private Declare Function DrawText Lib "user32" _
       Alias "DrawTextA" _
       (ByVal hdc As Long, _
       ByVal lpStr As String, ByVal nCount As Long, _
      lpRect As RECT, ByVal wFormat As Long) As Long 
Private Const DT_CALCRECT = &H400 

Public Property Let DropDownWidth(ByRef cboThis As ComboBox, ByVal lWidth As Long) 
    SendMessageLong cboThis.hwnd, CB_SETDROPPEDWIDTH, lWidth, 0 
End Property 

Public Property Get DropDownWidth(ByRef cboThis As ComboBox) As Long 
Dim lW As Long 
    DropDownWidth = SendMessageLong(cboThis.hwnd, CB_GETDROPPEDWIDTH, 0, 0) 
End Property 

Public Sub DropDownWidthFromContents( _
        ByRef cboThis As ComboBox, _
        Optional ByVal lMaxWidth = -1 _ 
    ) 
Dim i As Long 
Dim tR As RECT 
Dim lW As Long 
Dim lWidth As Long 
Dim lHDC As Long 

    ' Evaluate the width of each item in the 
    ' combo box: 
    
    ' First set the combo's parent form font to the 
    ' combo font: 
    With cboThis.Parent.Font 
        .Name = cboThis.Font.Name 
        .Size = cboThis.Font.Size 
        .Bold = cboThis.Font.Bold 
        ' Surely you don't have a combo box with 
        ' italic font? 
        .Italic = cboThis.Font.Italic
        .CharSet = cboThis.Font.CharSet
    End With 
    ' Cache the HDC of the parent form for speed: 
    lHDC = cboThis.Parent.hdc 
    
    ' Loop through each combo box list item & get its 
    ' width, storing the largest: 
    For i = 0 To cboThis.ListCount - 1 
        DrawText lHDC, cboThis.List(i), -1, tR, DT_CALCRECT 
        lW = tR.Right - tR.Left + 8 
        If (lW > lWidth) Then 
            lWidth = lW 
        End If 
    Next i 
    
    ' Don't allow width to exceed specified max 
    ' width, or the width of the screen: 
    If lMaxWidth <= 0 Then 
        lMaxWidth = Screen.Width \ Screen.TwipsPerPixelX - 16 
    End If 
    If (lWidth > lMaxWidth) Then 
        lWidth = lMaxWidth 
    End If 
    
    ' Combo box looks a bit strange when the 
    ' drop down portion is smaller than the 
    ' combo box itself: 
    If (lWidth < cboThis.Width \ Screen.TwipsPerPixelX) Then 
        lWidth = cboThis.Width \ Screen.TwipsPerPixelX 
    End If 
    
    ' Set the drop down width: 
    DropDownWidth(cboThis) = lWidth 
End Sub 

To try out a the function, add a Combo box, a Label and three Command buttons to your project's form. Set the captions for the command buttons as follows:

• Command1 A&dd String
• Command2 &Calc Width
• Command3 &Set Width...

Then add this code to the form:

Private Sub Command1_Click() 
Dim sI As String 
    sI = InputBox("Enter string", , "New item") 
    If (sI <> "") Then 
        Combo1.AddItem sI 
    End If 
End Sub 

Private Sub Command2_Click() 
    DropDownWidthFromContents Combo1 
    Label1.Caption = DropDownWidth(Combo1) 
End Sub 

Private Sub Command3_Click() 
Dim sI As String 
    sI = InputBox("Enter width", , DropDownWidth(Combo1)) 
    If IsNumeric(sI) Then 
        DropDownWidth(Combo1) = CLng(sI) 
        Label1.Caption = DropDownWidth(Combo1) 
    End If 
End Sub 

Private Sub Form_Load() 
    Label1.Caption = DropDownWidth(Combo1) 
End Sub 

Start the project. The width of the combo box wil lbe added to the label control. You can use the Add String button to add new items to the combo box, Calc Width to automatically set the drop down width to the control's contents and Set Width to set your own width. Note that all widths are specified in pixels.