McBasic™ 0.7.881 · Build 881 · 11 min read

Controls · Visual control

ComboBox

Populate a ComboBox and handle selection changes.

45 properties20 events1 methodsDefault: Change

Build the ComboBox lesson Properties Events Methods

Use it in a Form#

A selection index identifies a position, not a stable business ID. Use the initial items to understand Change first; then use the ChoiceBinding lesson for typed values backed by records. Handle the unselected state before reading an item.

Add ComboBox to its intended parent and name it cboChoice for this example:

Property	Example value
`Items`	`"First choice\nSecond choice\nThird choice"`
`Sorted`	`True`
`DropDownStyle`	`"DropDownList"`
`MaxDropDownItems`	`6`
`Padding`	`"8,4,8,4"`
`SelectedIndex`	`0`
`TabStop`	`True`

A complete handler from Forms/frmMain.bas. The linked lesson includes its surrounding controls, declarations and helpers.

Forms/frmMain.bas

Private Sub cboChoice_Change()
    Dim itemList As Collection
    Dim selected As Variant
    Set itemList = cboChoice.Items
    selected = cboChoice.SelectedItem
    If cboChoice.SelectedIndex >= 0 Then
        lblStatus.Caption = "Selection changed in the ComboBox."
    Else
        lblStatus.Caption = "No item is selected."
    End If
End Sub

Properties#

Contract defaults are shown below. Where a new control has a different Designer starting value, that value is listed separately.

`Left`

DoubleDefault: 0

Horizontal position in device-independent points, relative to the parent container.

Range: -100000 to 100000.

`Top`

DoubleDefault: 0

Vertical position in device-independent points, relative to the parent container.

Range: -100000 to 100000.

`Width`

DoubleDefault: 180

Control width in device-independent points.

Range: 0 to 100000.

`Height`

DoubleDefault: 32

Control height in device-independent points.

Range: 0 to 100000.

`MinWidth`

DoubleDefault: 0

Minimum control width in device-independent points; 0 lets the parent layout choose.

Range: 0 to 100000.

`MinHeight`

DoubleDefault: 0

Minimum control height in device-independent points; 0 lets the parent layout choose.

Range: 0 to 100000.

`MaxWidth`

DoubleDefault: 100000

Maximum control width in device-independent points.

Range: 0 to 100000.

`MaxHeight`

DoubleDefault: 100000

Maximum control height in device-independent points.

Range: 0 to 100000.

`TabIndex`

LongDefault: 0

Keyboard navigation order within the parent container; lower values come first.

Range: 0 to 100000.

`TabStop`

BooleanDefault: True

Whether the ComboBox participates in keyboard focus traversal.

`ZIndex`

LongDefault: 0

Stacking order among sibling controls; larger values appear in front. Equal values preserve document order.

Range: -100000 to 100000.

`Anchor`

StringDefault: "Left,Top"Not in InspectorNot serialized

Edges kept at their authored distance when the parent resizes. Use a comma-separated combination of Left, Top, Right and Bottom; Dock overrides the effective anchor without deleting it.

`Dock`

StringDefault: "None"

Automatic placement within the parent: None, Left, Top, Right, Bottom or Fill. Dock overrides effective Anchor layout without deleting the stored anchors.

`Margin`

StringDefault: "0"

External spacing as one non-negative DIP value or Left,Top,Right,Bottom.

`Cursor`

StringDefault: "Default"

Pointer shown over the control: Default, Arrow, Hand, IBeam, Cross, Wait, Help, SizeAll, SizeNS, SizeWE, SizeNWSE, SizeNESW or NotAllowed.

`Opacity`

DoubleDefault: 1

Visual opacity from 0 (transparent) to 1 (opaque).

Range: 0 to 1.

`DesignLocked`

BooleanDefault: FalseDesigner only

Prevents movement and resizing in the Designer without changing runtime interaction.

`Visible`

BooleanDefault: True

Whether the control is shown in the running application.

`Enabled`

BooleanDefault: True

Whether the control accepts user interaction in the running application.

`HitTestVisible`

BooleanDefault: True

Whether the running control participates in pointer hit testing. The control remains selectable in the Designer.

`AllowDrop`

BooleanDefault: False

Whether this running control accepts application drag-and-drop operations; Designer movement is separate.

`DragMode`

LongDefault: 0

VB control drag: 0 Manual (code starts a drag with the Drag method) or 1 Automatic (a left-button press starts a drag, and the control raises no Click, MouseDown or MouseUp for that press).

Range: 0 to 1.

`DragIcon`

StringDefault: ""

Case-insensitive name of a declared project image resource shown under the pointer while this control is dragged; empty shows a grey outline of the control.

`Font`

StringDefault: ""

Font as Family|Size or Family|Size|Regular/Bold|Normal/Italic, size 6–96 DIP. Empty uses the theme font; System uses the theme family.

`ForeColor`

StringDefault: ""

Text color as #RRGGBB. Empty uses the current macOS theme color.

`BackColor`

StringDefault: ""

Background color as #RRGGBB. Empty uses the current macOS theme color.

`Padding`

StringDefault: "4"

Internal spacing around the ComboBox content as one non-negative DIP value or Left,Top,Right,Bottom.

`AccessibleName`

StringDefault: ""

Name announced by assistive technology. Empty uses the stable control Name.

`AccessibleDescription`

StringDefault: ""

Additional help text announced by assistive technology.

`AutomationId`

StringDefault: ""

Stable automation identifier; empty uses the component Name.

`AccessibleRole`

StringDefault: "Auto"

Accessibility role override. Auto preserves the native semantic role; explicit values use the corresponding platform automation role.

`ToolTipText`

StringDefault: ""

Help text shown when the pointer rests over the running control; empty disables the tooltip.

`Tag`

StringDefault: ""

Application-defined text associated with this control; McBasic™ does not interpret it.

`Text`

StringDefault: ""

Editable text in DropDown mode; in DropDownList mode reads the selected display item and assignment selects an existing item.

`Items`

StringDefault: ""

Newline-separated display values; each non-empty line is one item in this bounded ComboBox slice.

Designer starting value: "Item 1\nItem 2\nItem 3".

`DisplayMember`

StringDefault: ""

Column shown when BASIC binds a BindingSource; empty uses the first result column.

`ValueMember`

StringDefault: ""

Column returned by SelectedValue when bound; empty uses DisplayMember.

`Sorted`

BooleanDefault: False

Sorts displayed items by deterministic case-insensitive ordinal text, with ordinal and source-order tie breakers.

`DropDownStyle`

StringDefault: "DropDownList"

DropDown permits free text; DropDownList requires an existing item.

`MaxDropDownItems`

LongDefault: 8

Preferred maximum visible item rows before the popup scrolls; the platform may further constrain popup height.

Range: 1 to 1000.

`SelectedIndex`

LongDefault: -1

Zero-based selected item index, or -1 when no item is selected.

Range: -1 to 100000.

Designer starting value: 0.

`MaxLength`

LongDefault: 0

Maximum length of text typed in the DropDown style, in UTF-16 units; 0 means unlimited. Ignored for DropDownList.

Range: 0 to 100000.

`AutoComplete`

BooleanDefault: False

In the DropDown style, completes typed text inline from Items and selects the completion; keep typing to replace it. DropDownList always selects by typed letters.

`ListIndex`

LongDefault: -1Not in InspectorNot serialized

Run-time alias of SelectedIndex (VB6 name): zero-based, -1 for no selection.

Range: -1 to 100000.

`Index`

LongDefault: -1Read only in BASICDesigner Index row

Position of this control in its control array, 0 to 32767. Several controls share one name only when every one of them has an Index. Absent from the layout, and -1 in code, when the control is not in an array.

Designer values: 0 to 32767. Clear the dedicated Index row for a non-array control; BASIC then reads -1.

Events and parameters#

Replace control with the object’s Name when creating a handler. ByRef arguments may be changed by your handler; ByVal arguments report an input value.