Erik Porter's Blog

Private Sub FindWidthForDropDown(ByVal ComboBox As ComboBox)
     Dim g As Graphics = ComboBox.CreateGraphics()
     Dim IsDatabound As Boolean = Not ComboBox.DataSource Is Nothing AndAlso ComboBox.DisplayMember <> ""
     Dim WidestWidth As Integer = ComboBox.DropDownWidth
     Dim ValueToMeasure As String
     Dim CurrentWidth As Integer

     For i As Integer = 0 To ComboBox.Items.Count - 1
          If IsDatabound Then
               ValueToMeasure = DirectCast(DirectCast(ComboBox.Items(i), DataRowView)(ComboBox.DisplayMember), String)
          Else
               ValueToMeasure = DirectCast(ComboBox.Items(i), String)
          End If

          CurrentWidth = CType(g.MeasureString(ValueToMeasure, ComboBox.Font).Width, Integer)
          If CurrentWidth > WidestWidth Then WidestWidth = CurrentWidth
     Next

     ComboBox.DropDownWidth = WidestWidth

     g.Dispose()
End Sub

private void findWidthForDropDown(ComboBox comboBox)
{
     bool isDatabound = comboBox.DataSource != null && comboBox.DisplayMember != null && comboBox.DisplayMember != "";
     int widestWidth = comboBox.DropDownWidth;
     string valueToMeasure;
     int currentWidth;

     using (Graphics g = comboBox.CreateGraphics())
     {
          for (int i = 0; i < comboBox.Items.Count; i++)
          {
               if (isDatabound)
                    valueToMeasure = (string)((DataRowView)comboBox.Items[i])[comboBox.DisplayMember];
               else
                    valueToMeasure = (string)ComboBox.Items[i];

               currentWidth = (int)g.MeasureString(valueToMeasure, comboBox.Font).Width;
               if (currentWidth > widestWidth) {widestWidth = currentWidth;}
          }
     }

     comboBox.DropDownWidth = widestWidth;
}