ComboBox Ocx

Purpose

Creates an Ocx ComboBox control in the current active form, window, or dialog.

Syntax

Ocx ComboBox name [= text$] [, id] [, x, y, b, h] [, style%]

text$:control text
id%:control identifier
x, y, b, h:iexp
style%:the control styles

Description

The control is a rectangle containing a list of strings (such as filenames) from which the user can select.

The ComboBox Ocx control has the following properties, methods, and events.

Properties

Appearance | BackColor | ForeColor | BorderStyle | Columns | DisableNoScroll | Enabled | Font | FontBold | FontItalic | FontStrikethru | FontUnderline | FontName | FontSize | Height, Width | HelpContextID | hWnd | Index | IntegralHeight |ItemData | Left, Top | List | ListCount | ListIndex | MouseCursor | MouseIcon | MousePointer | Name | NewIndex | Parent | Scrollbars | Selected | Sorted | Style | TabStop | Tag | Text | ToolTiptext | TopIndex | Visible | WhatsThisHelpID

Methods

AddItem | Clear | Find | FindExact | FindNext | InsertItem | Move | Refresh | RemoveItem | SetFocus | SetFont | TextHeight | TextWidth | ZOrder

Events

Click | DblClick | GotFocus | LostFocus | KeyDown, KeyUp | KeyPress | MouseDown | MouseUp | MouseMove | Scroll

There is no event which covers every eventually of the selected item being changed as the Click event only occurs when an object in the dropdown list is selected by using the mouse or by the up and down arrow keys, which means that occurences of the selected item being changed by physically typing in the value are missed. In the absence of a dedicated Change event, you can embed a call to Click in the KeyUp event which will effectively make the Click take on this role.

Remarks

The ComboBox object lacks some of the functionality that can be found in VB6 and most other programming languages which use it as an object; this can be overcome by using the SendMessage() API as follows:

• To find the position of Selstart (the cursor position) and SelEnd (the end of blocked text, if any) in the edit box, use ~SendMessage(cmb.hWnd, CB_GETEDITSEL, selstart, selend).


• To set the position of Selstart and SelEnd, use: ~SendMessage(cmb.hWnd, CB_SETEDITSEL, 0, MakeLong(selstart, selend)).


• The editbox can be resized vertically by using ~SendMessage(cmb.hWnd, CB_SETITEMHEIGHT, -1, newheight%).


• The number of characters that can be entered into the edit box can be limited by using ~SendMessage(cmb.hWnd, CB_LIMITTEXT, limit, 0).


• A 'cue banner' can be added to the edit box using the code below:

  Ocx ComboBox cmb = , 10, 10, 200, 22

  Local cb$ = "[Cue Banner]"

  Const CBM_FIRST = &1700

  Const CB_SETCUEBANNER = (CBM_FIRST + 3)

  ~SendMessage(cmb.hWnd, CB_SETCUEBANNER, 0, UNI$(cb$))

  Do : Sleep : Until Me Is Nothing

   

  Function UNI$(ansi$) // Acknowledgements to Peter Heinzig

  Local lUni As Variant = CVar(ansi) : Return Peek$({V:lUni + 8}, Len(lUni) * 2) + #0

  EndFunction



• The dropdown list of the ComboBox can be opened programmatically using ~SendMessage(cmb.hWnd, CB_SHOWDROPDOWN, True, 0), closed using ~SendMessage(cmb.hWnd, CB_SHOWDROPDOWN, False, 0), and the state of the dropdown list can be obtained using ~SendMessage(cmb.hWnd, CB_GETDROPPEDSTATE, 0, 0).


• The number of items visible when the dropdown list is shown can be altered using MessageProc event of the parent window or form to catch the CBN_DROPDOWN event of the ComboBox object as illustrated in the example below. A variation of this code can also be used to catch all the other ComboBox events as well.

  // ComboBoxes which are to have full lists must have 'Full' somewhere in their Tag property.

  // To set a 'Minimum Visible' limit, the string 'MinVisxxx' (where xxx is the number of entries to show) must be somewhere in the Tag property.

  // --- NB The value of the minimum visible entries can only be greater than 8.

  Type COMBOBOXINFO

  - Long cbSize

  rcItem As RECT

  rcButton As RECT

  - Long stateButton

  - Long hwndCombo

  - Long hwndItem

  - Long hwndList

  EndType

  Type RECT

  - Long Left, Top, Right, Bottom

  EndType

  Const CB_GETCOMBOBOXINFO = 0x0164

  OpenW 1

  Local n As Int32

  Ocx ComboBox cmb = "", 10, 60, 100, 22 : cmb.Tag = "Full" : For n = 1 To 20 : cmb.AddItem "Item no " & Iif(n < 10, " ", "") & Trim(n) : Next n

  Ocx ComboBox cmb2 = "", 10, 120, 100, 22 : cmb2.Tag = "MinVis012" : For n = 1 To 20 : cmb2.AddItem "Item no " & Iif(n < 10, " ", "") & Trim(n) : Next n

  Ocx ComboBox cmb3 = "", 10, 180, 100, 22 : For n = 1 To 20 : cmb3.AddItem "Item no " & Iif(n < 10, " ", "") & Trim(n) : Next n

  Do : Sleep : Until Win_1 Is Nothing

   

  Sub Win_1_MessageProc(hWnd%, Mess%, wParam%, lParam%, retval%, ValidRet?)

  Try

  If Mess% = WM_COMMAND And HiWord(wParam%) = CBN_DROPDOWN

  // Check to see if control is a ComboBox

  Local cn$ = Space(100) : ~GetClassName(lParam%, V:cn$, 100)

  If ZTrim(Mid(cn$, 2)) = "ComboBox"

  // Check to see if ComboBox list to be shown in full

  Local cb As Control : Set cb = OCX(lParam%)

  If InStr(Lower(cb.tag), "full") + InStr(Lower(cb.tag), "minvis") <> 0

  // Retrieve ComboBox Structure Information

  Local cbi As COMBOBOXINFO : cbi.cbSize = SizeOf(COMBOBOXINFO) : ~SendMessage(lParam%, CB_GETCOMBOBOXINFO, 0, cbi)

  // Retrieve ListBox rectangle coordinates

  Local lbr As RECT : ~GetWindowRect(cbi.hwndList, lbr)

  // Retrieve Item Count and Height values

  Local Int32 ct, h : h = SendMessage(cbi.hwndList, LB_GETITEMHEIGHT, 0, 0)

  If InStr(Lower(cb.tag), "full") <> 0 : ct = SendMessage(cbi.hwndList, LB_GETCOUNT, 0, 0)

  Else : ct = InStr(Lower(cb.tag), "minvis") : cn$ = Mid(cb.tag, ct, 9) : ct = Right(cn$, 3)

  EndIf

  If ct > 8 // If Item Count greater than default 8 entries

  // Calculate new height for ListBox

  h = (h * ct) + (Screen.cyBorder * 2)

  // Redraw ListBox

  ~MoveWindow(cbi.hwndList, lbr.Left, lbr.Top, lbr.Right - lbr.Left, h, 1)

  // Stop GB32 processing this message

  ValidRet? = True

  // Clear structures

  Clr cbi, lbr

  EndIf

  EndIf

  EndIf

  EndIf

  Catch

  // Include error message here if required

  EndCatch

  EndSub

  
  The CB_SETMINVISIBLE (&1701) and CB_GETMINVISIBLE (&1702) messages are available but GB32 overrides their actions when redrawing the dropdown list.

See Also

Ocx, OcxOcx

Animation, CheckBox, Command, CommDlg, Form, Frame, Image, ImageList, Label, ListBox, ListView, MonthView, Option, ProgressBar, RichEdit, Scroll, Slider, StatusBar, TabStrip, TextBox, Timer, TrayIcon, TreeView, UpDown

{Created by Sjouke Hamstra; Last updated: 08/03/2018 by James Gaite}