Connecting parts

Constructing your first visual application introduces you to making connections between parts. In this section you explore the different types of connections and all that you can do with them. It's best to follow along in the Composition Editor as the different connection types are described and try any examples discussed. Creating and experimenting with connections is an excellent way to learn how to use them.

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. You set these when you create the connections, but you can edit the connection and change them later. To see how, go to

•	Changing the Properties of connections,

•	Manipuating connections and

•	Connection parameters.

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If a part's action, attribute, or event does not appear in the part's preferred connection list, in its part or connection pop-up menu, you can select Connect>All Features from the part's pop-up or connection pop-up menu to display a complete list. The list of actions, attributes and events displayed in the All Features list represents a part's complete public interface

There are seven types of connections:

•	Attribute-to-attribute

Attribute-to-attribute connections link two data values together so that when one value changes, the other value changes too.

•	Event-to-action

Event-to-action connections perform an action when an event occurs.

•	Event-to-script

Event-to-script connections run a script whenever an event occurs.

•	Attribute-from-script

Attribute-from-script connections run a script whenever an attribute value needs to be calculated.

•	Parameter-from-attribute

Parameter-from-attribute connections use the value of an attribute as the parameter to a connection.

•	Parameter-from-action

Parameter-from-action connections use the result of an action as a parameter to a connection.

•	Parameter-from-script

Parameter-from-script connections run a script whenever a parameter to a connection is required.

For more information about scripts, refer to the VA Smalltalk User's Guide.