Oracle Visual Builder: Applications That Outlive Their First Release · Module 4 · Variables, types and where state lives
The event that fires when state changes
Lesson 40 of 176 · 3 min
Reacting to a value changing, and THE LOOP YOU CREATE WHEN TWO OF THEM REACT TO EACH OTHER. A variable can have an action chain attached that runs whenever it changes — which is powerful, useful, and the easiest way in this product to build something that will not stop. WHAT IT IS FOR IS THE GENUINE CASCADE. A country is chosen, so the list of regions must reload. A date range moves, so a chart must re-fetch. Writing that as "when this changes, do that" is exactly right, and the alternative — remembering to fire the reload from every place the country can be set — is the incomplete-fix pattern of Lesson 6. THE LOOP IS WHAT HAPPENS WHEN THE REACTION WRITES SOMETHING THAT IS ALSO WATCHED. A changes, its handler sets B, B's handler sets A. Neither line is wrong on its own and neither developer wrote a…
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In this module: Module 4 · Variables, types and where state lives
- 1What a variable is here
- 2The scopes, and what each one meansFree preview
- 3Choosing a scope, deliberately
- 4Types, and why you should declare them
- 5Types that mirror a service
- 6Computed values and expressions
- 7Variables that persist
- 8The event that fires when state changes
- 9State that four pages need
- 10Naming state so it is findable
- 11What breaks: four state failures
- 12Lab briefing · Move state and watch it break