TComboBox class

In unit StdCtrls

Implements a control with an edit box and a drop-down list allowing one of several options to be chosen.

Declaration

pascal

TComboBox = class(TCustomComboBox)

Inheritance

Description

TComboBox is a TCustomComboBox descendant which implements the a combo-box component in the LCL (Lazarus Component Library).

A combo-box is visually represented as an edit control and a scrollable list of items which can be selected. The list can always be visible, or opened when needed using a drop-down indicator. In addition, the items displayed on the control are drawn using using the built-in mechanisms for the widgetset class or using an owner-drawn style.

Despite similarities in appearance to TCustomEdit and TCustomList, the class inherits no properties from these classes (Delphi compatible).

Use Items to access the entries displayed in the drop-down list. Use AddItem or AddHistoryItem to add entries to the list of items. Use OnGetItems to dynamically populate the Items in the control when the drop-down list is displayed.

The selectable values in Items can be maintained at design-time by clicking on the ellipsis character (...) displayed next to Items in the Object Inspector.

The Text property reflects the text entered directly into the edit box, or selected either manually or by auto-completion from the Items in the list. At run-time, the entry selected from the list replaces the text in the edit box, and ItemIndex holds the (zero-based) index number of the selected item. If no value is selected from the drop-down list, the default text (if any) remains for any information typed directly into the control Text, and ItemIndex takes the value of -1.

Use Style to control the display style and drawing mechanism enabled for the drop-down list on the control.

Use AutoDropDown, AutoComplete, AutoCompleteText, and AutoDropDown to control the behavior of the edit box and its interaction with the drop-down list on the control.

Use ItemHeight and ItemWidth to control the appearance for the Items displayed on the drop-down list.

The Height property in TCustomComboBox / TComboBox cannot be changed for some platforms, including Windows and macOS. It is best to set AutoSize to True to ensure consistent size handling on the supported platforms.

Changing the value in BorderStyle to bsNone has no effect for the Windows widgetset. It is not possible to remove the border on the Windows platform.

Properties

`Align`	published	Specifies the placement of the control on its Parent control.
`Anchors`	published	The set of anchor definitions for this control.
`ArrowKeysTraverseList`	published	Indicates if keyboard Arrow (or cursor) keys can be used to move through the list.
`AutoComplete`	published	Positions the list box using partial text matching.
`AutoCompleteText`	published	Options for the behavior of the Auto-Complete feature.
`AutoDropDown`	published	Makes the drop-down list appear as soon as the user starts entering text.
`AutoSelect`	published	Selects the entire content of the edit box when the control receives the focus.
`AutoSize`	published	Allows automatic adjustment of the size for the control, according to its content.
`BidiMode`	published	Indicates whether text controls use in bi-directional reading.
`BorderSpacing`	published	Determines the inner and outer border spacing for this control.
`BorderStyle`	published	Indicates the border style displayed around the control.
`CharCase`	published	Indicates the case conversion applied to the value entered in the edit box for the control.
`Color`	published	The background color for the control.
`Constraints`	published	Contains the minimum and maximum Width and Height for the control.
`DoubleBuffered`	published	When enabled, it reduces flicker when the control is painted.
`DragCursor`	published	The cursor shape shown during a drag operation.
`DragKind`	published	Indicates the action performed for a drag operation: drag-and-drop or drag-and-dock.
`DragMode`	published	Determines how a drag operation is started for the control.
`DropDownCount`	published	The maximum number of Items visible in the drop-down list for the control.
`Enabled`	published	Determines whether the control responds to mouse or keyboard input.
`Font`	published	The font to be used for text display in this control.
`ItemHeight`	published	The default height of an item in the drop-down for the control.
`ItemIndex`	published	The index of the currently selected item, or -1 if no item is selected.
`Items`	published	The list of items displayed in the combo-box control.
`ItemWidth`	published	The minimum width of the items in the drop-down list.
`MaxLength`	published	The maximum length for text entered in the edit box for the control.
`ParentBidiMode`	published	Indicates whether the BiDiMode settings in the Parent control are used.
`ParentColor`	published	Uses the Color from the Parent control, when enabled.
`ParentDoubleBuffered`	published	Value for the DoubleBuffered property in a Parent control.
`ParentFont`	published	Indicates if the Font from the Parent control is used in the control.
`ParentShowHint`	published	If True, the value of ShowHint for the control will be the same as the one from the Parent. Default is True.
`PopupMenu`	published	A context-sensitive menu that pops up when the right mouse button is clicked over this control.
`ReadOnly`	published	Disallows free-form entry of Text into the combo-box edit field.
`ShowHint`	published	Enables Hint display for the control.
`Sorted`	published	Determines whether the list entries are sorted in alphanumeric order.
`Style`	published	Controls the appearance and behavior for the combo-box.
`TabOrder`	published	Indicates the navigation order for the control when the user presses the Tab or Shift+Tab key.
`TabStop`	published	Enables or disables keyboard navigation using the Tab or Shift+Tab keys.
`Text`	published	The value in the edit box for the control.
`TextHint`	published	Default hint text shown when the Text property is empty for the control.
`Visible`	published	Allows the control, and all of its children, to be displayed or hidden.

Events

`OnChange`	published	Event handler signalled for user changes to the text in the edit box.
`OnChangeBounds`	published	Event handler signalled when the Bounds for the control have been changed.
`OnClick`	published	Notification handler for mouse clicks.
`OnCloseUp`	published	Handler invoked when the drop-down list closes.
`OnContextPopup`	published	Invoked when a context-sensitive pop-up menu is requested.
`OnDblClick`	published	Event handler signalled when a mouse double click occurs in the control.
`OnDragDrop`	published	Event handler signalled when an object is dropped onto the control.
`OnDragOver`	published	Event handler signalled when a control is dragged over the control instance.
`OnDrawItem`	published	Handler for special painting of an item (in owner-draw mode).
`OnEndDrag`	published	Event handler signalled for the end of a drag-drop operation.
`OnDropDown`	published	Handler invoked when the list has dropped down.
`OnEditingDone`	published	Event handler signalled when editing is completed for the control.
`OnEnter`	published	Event handler signalled when the control receives focus.
`OnExit`	published	Event handler signalled when the control loses focus.
`OnGetItems`	published	Handler invoked when widgetset items list can be populated.
`OnKeyDown`	published	Event handler signalled for key down keyboard events.
`OnKeyPress`	published	Event handler signalled for character data entered by the user.
`OnKeyUp`	published	Event handler signalled when a key up event has occurred for the control.
`OnMeasureItem`	published	Handler invoked when the height for an item is needed.
`OnMouseDown`	published	Event handler signalled when a mouse down event is handled for the control.
`OnMouseEnter`	published	Event handler signalled when the mouse pointer has entered the control.
`OnMouseLeave`	published	Event handler signalled when the mouse pointer has left the control.
`OnMouseMove`	published	Event handler signalled when the mouse pointer is moved in the control.
`OnMouseUp`	published	Event handler signalled when a mouse up event is handled for the control.
`OnMouseWheel`	published	Event handler for mouse wheel turned.
`OnMouseWheelDown`	published	Event handler signalled for a downward movement of the mouse wheel.
`OnMouseWheelUp`	published	Event handler signalled for an upward movement of the mouse wheel.
`OnSelect`	published	Handler invoked when an item is selected.
`OnStartDrag`	published	Event handler signalled for the start of a dragging operation.
`OnUTF8KeyPress`	published	Handler for a character entered by the user.