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| Purpose: | This object combines an input area with a list box and allows the user to enter a selection by typing text or by choosing an item from the list. |
Description
Three types of Combo box are provided by the Style property which may be 'Drop' (the default), 'Simple' or 'DropEdit'.
The Items property specifies the list of items which are displayed in the list box and from which the user can choose.
The SelItems property is a Boolean vector which specifies which (if any) of the items is selected. When the user chooses an item from the list, it is copied to the edit field and a Select event is generated. At this point you may use SelItems to identify the chosen item. You can also use SelItems to pre-select the contents of the edit field.
If the Style is 'Simple' or 'DropEdit', the user may type text into the edit field. In these cases, the contents of the edit field may also be specified or queried using the Text property.
Note that if the user first selects an item from the list box, then changes it in the edit field, the entry in the list box is automatically deselected. There is therefore no conflict between the value of Text and the value of SelItems.
Warning: Windows truncates the contents of the edit field (reflected in the value of the Text property) to 510 characters.
For a Combo with Style 'Simple', the Index property specifies or reports the position of Items in the list box as a positive integer value. If Index has the value "n", it means that the "nth" item in Items is displayed on the top line in the list box. Note that Index can only be set using ⎕WS and not by ⎕WC and is ignored if all the Items fit in the list box. The default value for Index is ⎕IO.
The SelText property identifies the portion of the edit field that is highlighted. It is not applicable to a Combo with Style 'Drop' as the user cannot enter or change data in its edit field.
The height of a Combo object with Style 'Drop' or 'DropEdit' is defined in a manner that is different from other objects. The height of the edit field is fixed, and is dependent only upon the size of the font. The height of the associated drop-down list box is determined by the Rows property. The first element of the Size property (height) is ignored. For a Simple combo box (whose listbox is permanently displayed), the overall height is determined by the first element of Size. Rows is a "read-only" property.
The VScroll property specifies whether or not a vertical scrollbar is provided. The default value 0 means no scrollbar, setting VScroll to ¯1 or ¯2 specifies that the Combo has a vertical scrollbar.
If the Style is 'Simple' or 'DropEdit', the HScroll property determines whether or not the edit field may be scrolled. If HScroll is 0, the data is not scrollable, and the user cannot enter more characters once the field is full. If HScroll is ¯1 or ¯2 the field is scrollable, and there is no limit on the number of characters that can be entered. In neither case however is a horizontal scrollbar provided. If Style is 'Drop', the user is not allowed to enter data into the edit field anyway, and the value of HScroll is ignored.
VScroll and HScroll may only be set when the object is created and may not subsequently be changed.
Note that when you change the Items property using ⎕WS, the Text, SelItems and SelText properties are all reset to their default values.
The Combo object will report a Select event (if enabled) when the user chooses an item from the list box. It will generate a Change event (if enabled) when the user manually alters the contents of the edit field and then changes the focus to another object.