Persisting state

The values a user enters, such as the selected tab, a switch, a slider or the text of a field, live in Fusion values inside each component. When you rebuild the interface, for example to change theme or layout, those values are gone with the old components.

Persist keeps them. You give the app a store, and the values live in the scope of the store, so a rebuild finds them again.

Using a store

local store = Pantheon.Persist.createStore(rootScope) -- (1)!

local function rebuild()
    Pantheon.Persist.Provide(store, function()
        -- build the interface: every Switch, Tabs, Slider... reuses its value
    end)
end

1. The store keeps its values in rootScope, so they outlive the scopes of the individual builds.

Without a store, every component creates its own plain values, as usual.

How a component finds its value

A component looks up its state:

• by its Id, when it has one: Id = "settings.sound";
• otherwise by its kind and the order it was created in during the build: the third Switch is Switch#3.

A rebuild runs the same code in the same order, so the order is stable. Interface that changes the order, such as a switch that is only built when a condition holds, should have explicit Ids.

What is not kept

A property you give as a state is left alone. If you pass Value = someValue, you own that state, and the component does not store it.

Components that keep state

Switch, Checkbox, RadioGroup, ChoiceGroup, Select, MultiSelect, Slider, RangeSlider, DatePicker, TimePicker, Tabs, SegmentedControl, Collapsible, TreeView, StarRating, Pagination, NavigationRail, TextField (the text typed into it), ColorPicker and GradientPicker.

See Persist for the functions.