Reactive user interfaces

Another trick you will definitely want up your sleeve at some point is a reactive user interface. This enables you to change your UI (for example, the number or content of radio buttons) based on reactive functions.

For example, consider an application that I wrote related to survey responses across a broad range of health services in different areas. The services are related to each other in quite a complex hierarchy, and over time, different areas and services respond (or cease to exist, or merge, or change their name), which means that for each time period, the user might be interested in, there would be a totally different set of areas and services. The only sensible solution to this problem is to have the user tell you which area and date range they are interested in and then give them back the correct list of services that have survey responses within that area and date range.

The example we're going to look at is a little simpler than this, just to keep from...