Concepts

The Dyalog APL GUI is based upon four important concepts; objects, properties, events and methods.

Objects

Objects are instances of classes that contain information and provide functionality. Most Dyalog APL objects are GUI objects that may be displayed on the screen and with which you can interact. An example of an object is a push-button (an instance of class Button) which you may press to cause the program to take a particular action. Objects are defined in hierarchies.

Objects are also namespaces and may contain functions, variables, and indeed other namespaces. This allows you to store the code and data that is required by a given object within that object. Functions and variables stored in an object are hidden and protected from conflicts with functions and variables in the outside workspace and with those in other objects.

Properties

Each object has an associated set of properties which describe how it looks and behaves. For example, a Button has a property called Caption which defines the character string to be displayed in it. It also has a property called Type which may be Push (the button appears to move in and out when it is pressed), Radio (the button has two states and may be toggled on and off); and so forth.

Events

During interaction with the user, an object is capable of generating events. There are essentially two types of event, raw events and object events. Raw events are typically associated with a particular hardware operation. Pressing a mouse button, pressing a key on the keyboard, or moving the mouse pointer are examples of raw events. An object event is generated by some action that is specific to the object in question, but which may typically be achieved by a variety of hardware operations.

An example is the Select event. For a Button object, this event is generated when the user presses the Button. In MS-Windows, this can be done in several ways. Firstly, the user may click the left mouse button over the object. Secondly, under certain circumstances, the Select event can be generated when the user presses the Enter key. Finally, the event will occur if the user presses a "short-cut" (mnemonic) key that is associated with the Button.

Methods

Methods are effectively functions that an object provides; they are things that you may invoke to make the object do something for you. In Dyalog APL, the distinction between methods and events is tenuous, because events also make objects perform actions and you may generate events under program control. For example, a Scroll event is generated by a scrollbar when the user moves the thumb. Conversely, you can make a scrollbar scroll by generating a Scroll event. Nevertheless, the concept of a method is useful to describe functions that can only be invoked by a program and are not directly accessible to the user.

Objects

The following objects are supported.

System Objects
Root	system-level object
Printer	for hard-copy output
Clipboard	provides access to Windows clipboard
Container Objects
CoolBand	represents a band in a CoolBar
CoolBar	a container for CoolBand objects
Form	top-level Window
MDIClient	container for MDI windows
SubForm	acts as an MDI window or a constrained Form
Group	a frame for grouping Buttons and other objects
Static	a frame for drawing and clipping graphics
StatusBar	ribbon status bar
TabBar	contains TabBtns (tabs)
TabControl	contains TabButtons (tabs)
ToolBar	ribbon tool bar
ToolControl	standard Windows tool control
PropertySheet	contains PropertyPages
PropertyPage	tabbed or paged container for other controls
Splitter	divides a container into panes
Menu
MenuBar	pull-down menu bar
Menu	pop-up menu
MenuItem	selects an option or action
Separator	separator between items
Action
Button	selects an option
ToolButton	performs an action or selects an option
TabBtn	selects a tabbed SubForm
TabButton	selects a tabbed SubForm
Scroll	scroll bar
UpDown	spin buttons
Locator	graphical (positional) input device
Timer	generates events at regular intervals
Information
Label	displays static text
StatusField	displays status information
MsgBox	displays a message box
TipField	displays pop-up context sensitive help
ProgressBar	displays the progress of a lengthy operation
Input & Selection
Calendar	displays a month calendar control
Grid	displays a data matrix as a spreadsheet
Edit	text input field
RichEdit	text input with word-processing capabilities
Spinner	input field with spin buttons
List	for selecting an item
ListView	displays a collection of items for selection
Combo	edit field with selectable list of choices
TreeView	displays a hierarchical collection of items
TrackBar	a slider control for analogue input/output
FileBox	prompts user to select a file
Resource
Font	loads a font
Bitmap	defines a bitmap
Icon	defines an icon
ImageList	defines a collection of bitmaps or icons
Metafile	loads a Windows Metafile
Cursor	defines a cursor
Graphical Output
Circle	draws a circle
Ellipse	draws an ellipse
Marker	draws a series of polymarkers
Poly	draws lines
Rect	draws rectangles
Image	displays Bitmaps, Icons and Metafiles
Text	draws graphical text
Miscellaneous
ActiveXContainer	represents the application hosting a Dyalog ActiveXControl
ActiveXControl	represents an ActiveX control written in Dyalog
HTMLRenderer	displays HTML content
NetClient	provides access to .NET Classes
NetControl	instantiates a .NET Control.
NetType	exports an APL namespace as a Net Class
OCXClass	provides access to OLE Custom Controls
OLEClient	provides access to OLE Automation objects
OLEServer	enables APL to act as an OLE Automation server
SM	specifies a window for ⎕SM (character mode interface)
TCPSocket	provides an interface to TCP/IP sockets

Implementation Overview

The Dyalog APL GUI is implemented by the following system functions :

⎕DQ	Dequeue	processes user actions, invoking callbacks
⎕NQ	Enqueue	generates an event under program control
⎕WC	Create Object	creates new object with specified properties
⎕WG	Get Properties	gets values of properties from an object
⎕WN	Object Names	reports names of all children of an object
⎕WS	Set Properties	sets values of properties for an object

GUI Objects are a special type of namespace and have a name class of 9. They may therefore be managed like any other workspace object. This means that they can be localised in function headers and erased with ⎕EX. GUI objects are saved with your workspace and reappear when it is loaded or copied.