2008-06-28

Implementing screen flows

On EclipseCon '08 I had a presentation named Lessons Learned from an Enterprise RCP Application. As said then, one of the major differences between most Eclipse IDEs and many enterprise applications is the way the performed tasks are controlled by the end-users:
  • In IDEs - and many more technical RCP applications - most task is controlled by creativity. E.g. you get a task - create this or change that - and then it is more or less up to you how you want to solve it. You might have a number of large-scope processes - like you have to check in your work and change the state of issue reports - but nothing on the smaller scale.
  • In many enterprise RCP application most tasks are controlled by processes. E.g. you have an exact description of how to perform most tasks - like create new account or change the payment plan. Processes are here centered on the smaller scale as well on the larger scale - like in which sequence data must be entered when making a new credit agreement.
Out of the box Eclipse RCP supports wizards as the primary type of processes engine. In the default implementation, wizards have one major limitations compared with what you would like to see in many enterprise applications: they are modal and thus you can only have one active process at any one time.

That does not match well with many enterprise applications where the user must be able to 1) service phone calls in the middle of an on-going task and 2) alternate between a number of tasks...

The current wizard interface has a number of other problems as well:
  • The interface for a wizard page (IWizardPage) assumes that a page cannot be "stale" compared with the model - which of cause is fine as long as wizards are modal... Note that this is actually solved in another similar interfaces used in the Forms UI API (IFormPart).
  • The interface for a wizard page also makes the different pages aware of the previous and next pages as well as the actual control of the page which is a little peculiar when doing screen flows, where you might want a high degree of reuse of pages between processes.
  • The use of WizardPage.setControl() seems to be one of the major sources of problems when developing pages - people just forget :-(
Of cause the wizard implementation has one major point that speaks for it: the current UI design tools - like SWT Designer - understands wizard pages, but not whatever we invent.

Until now we have implemented the needed processes as needed, but now are going to implement a rather large number of processes - of which many will be quite similar, so we want to implement some framework to ease the work and to make the result more maintainable.

The question is now: what would you do here? Implement a new wizard viewer in a view that can show multiple concurrent wiards or implement a new (simplified) flow interface that matches the requirements exactly? For those of you that have implemented RCP applications already, what have you done in these?
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