Key concepts
VA Smalltalk takes advantage of visual programming paradigm, which enables you to develop software by assembling and connecting reusable components called parts.
The construction from parts technology is based on well-established techniques from other industries such as manufacturing. Just as electronic chips can be combined to form a functional board, and functional boards can be combined to form a computer, software parts can be combined to form composite parts, and then further combined to form applications.
Parts
In VA Smalltalk, a part is a self-contained software object with a well-defined public interface that establishes the features of the part.
There are three types of parts that you work with in VA Smalltalk:
Visual part
A part that has a visual appearance at run time. Visual parts, such as windows, push buttons, and entry fields, make up the user interface of an application. Visual parts can contain other visual parts, nonvisual parts, connections to other parts and to Smalltalk code. The Composition Editor is the primary tool used to create and modify visual parts.
Nonvisual part
A part that has no visual appearance at run time. A nonvisual part typically represents behaviors or data within an application. Nonvisual parts can contain other nonvisual parts, connections to other parts and to Smalltalk code. The Composition Editor is the primary tool used to create and modify nonvisual parts.
Smalltalk class
A Smalltalk class and associated methods may be used to implement behavior or represent data directly through the use of the Smalltalk language. The Script Editor is the primary tool used to create and modify Smalltalk classes.
A part's public interface determines how it can interact with other parts. The public interface of a part consists of the following types of features:
Attributes
Data that can be accessed by other parts. This data can represent any logical property of a part, such as the balance of an account, the size of a shipment, or the label of a push button.
Events
Signals that indicate something has happened, such as opening a window or changing an attribute's value.
Actions
Operations or functions that a part can perform. Actions can be triggered by connections from other parts.
Parts placed inside of other parts are called subparts. A part that contains other parts is called a composite part. All parts can be reused as subparts of composite parts.
Properties views
A Properties view provides a way to display and set the attributes and other options associated with a part or connection. In addition to part-specific properties, you can set data validation, layout, drag and drop, and help information. For example, you can add an OK push button and define it as the default push button by opening the properties view for the Push Button part and setting the value of the showAsDefault property to true. A part's properties view is displayed using the Properties window for a part.
Connections
Connections define how parts interact with each other as well as how parts interact with scripts. You can make connections between parts, scripts, and other connections. A connection has a source and a target. The point at which you start the connection is called the source; the point at which you end the connection is called the target.
There are seven types of connections:
Attribute-to-attribute
Link two data values together so that when one value changes, the other value changes too.
Event-to-action
Perform an action when an event occurs.
Event-to-script
Run a script whenever an event occurs.
Attribute-from-script
Run a script whenever an attribute value needs to be calculated.
Parameter-from-attribute
Use the value of an attribute as the parameter to a connection.
Parameter-from-action
Use the result of an action as a parameter to a connection.
Parameter-from-script
Run a script whenever a parameter to a connection is required.
For more details about the different types of connections, see
Connecting parts.
Scripts
VA Smalltalk includes a powerful object-oriented language named Smalltalk that you can use to extend your application logic. In VA Smalltalk, a script is a series of Smalltalk statements that implement an action for a part.
You create and edit scripts using the Script Editor, which gives you direct access to the Smalltalk language. Scripts are associated with the parts in which they were created. VA Smalltalk enables you to organize the scripts you write into categories.
Smalltalk Code
Using Smalltalk code, you can easily extend the behavior of a VA Smalltalk part. The following terms introduce you to some of the more common object oriented concepts you will encounter when using VA Smalltalk. For an introduction to writing Smalltalk code, see
the power of Smalltalk. For a more thorough understanding of this very robust programming language, refer to the
Programmer Reference in the online documentation and VA Smalltalk publications found at
Library web page.
A class specifies an object, including its data and behaviors. Methods, which are called scripts in VA Smalltalk, are executable code that implements the behavior or logic of a particular class.
A VA Smalltalk part is simply a class with some predefined data and behaviors that enables it to be edited visually in the
Composition Editor.
Last modified date: 07/23/2020