State fetch

A common pattern in GUIs is 'showing the data revealed by an API'. For example we might show the data in shopping site, or show account data about customers.

When doing this typically there is a navigation area which determines what is being looked at, and then multiple places that show information about what is being looked at. Each time the state is changed a decision needs to be made about whether to get more information from the backing API(s).

The strategy adopted is to have a 'tag' field in the state which describes the type of the display being shown. This tag is linked to a set of functions that allow state-fetcch to decide when to load state information.

Key Concepts

State

This uses the state defined in the project @focus-on/state. The state is a javascript object with one or more lens focused on different parts of it which allows it to be 'modified' using the usual 'immutable' meaning of modified (i.e. copied and the copy updated)

View

The state will have (names all configurable - the following is just the normal names)

• A view field that holds a string defining the current view. It is used as a key into the ViewState
• A mainItem that is either undefined or the current mainItem the view is focused on
• A selectionState that holds information allowing the mainItem to be fetched (e.g. one or more ids)

View state

Given the name of a view, the view state defines

• How to display it
• How to fetch it from the back end
• How to work out whether it needs to be fetched

Parent Views

Some views depend on parents, and the parent data has to be loaded first. For instance if we are displaying an item in a collection there could be a view for the collection which should be loaded before the item is loaded.

This is handled using parentView

setJsonUsingView

This is the helper method that makes it all work. This controls the rendering.

Generics in View

View store has the signature ViewStore<State, Element>. State is the javascript object that defines the state the view will be looking at. Element will usually be a JSX.Element, but is defined as a generic to avoid binding to any specific library. Thus you can use this with any version of react

Displaying the view

The @focuson/view-components project has the MainView component. It is bound to a particular version of react, but you can just copy it if you want a different version.