Introduction

As part of Requirements Gathering, Usecases describe the interaction between an actor and the system to be build. A user initiates (start) an Usecase through events from some UI control. In response to that, the system may request information from the user in order to complete (end) the Usecase. A Usecase specifies the control of that flow.

Building an application requires implementing all Usecases. View components are needed to execute usescases and will present the user with result information. In case of RIA, typically information is needed that is provided using application services.

Class Conversation can be used to implement the mediation process in which user interaction, information retrieval and information presentation is coordinated. Class Conversation provides an implementation of a coding pattern to facilitate this.

A conversion is a non-visual component. It encapsulates the flow of actions needed to complete a Conversation. Because it is not tied to any calling (visual) component, it can be (re)used anywhere in your application.

The following snippet shows a template that can be used to implement Conversation classes.

Class Template

public class YourUseCase extends Conversation
{
	override protected function begin():void {
		// do not forget to call this.end() in the last step of the conversation when completed with success
		// or to call this.stop() when the conversation completed with a failure
	}	
	override protected function checkPreconditions():Boolean {
		// check all variable values, raise exceptions or show warnings if values are not as specified
		// return true if conditions are met, return false otherwise
	}	
}

Example Flow

A typical basic sequence is:

a conversation is started by providing a Function to be called after completion
it checks its own preconditions and stops if that fails
it may inspect the shared Application Context for relevant objects
it asks the User (through Dialogs) for additional information if needed
the dialog calls back to the conversation to resume the flow
it checks whether the dialog was accepted or canceled
it asks a Service to perform some operation
the Service calls back to the conversation to resume the flow
it inspects the reply to see if it was successful
it stores (by key) result objects into the shared Application Context
any View that is bound to that key gets notified about changes
the conversation ends

Examples

ConversationExampleLogin