Register how an input is restored

A restorer turns the value stored in a snapshot into the message that the input's client-side binding understands, that is, what the matching update*Input() function would send. shinysnap ships restorers for the inputs of shiny, bslib, and shinyMatrix (see snap_restorers()); the default for everything else is list(value = value). Register your own for an input id or for a binding name (for example "shinyWidgets.pickerInput").

Usage

snap_restorer(x, fn, session = NULL)

snap_restorers(session = shiny::getDefaultReactiveDomain())

Arguments

x

An input id or a binding name, as reported in the snapshot's bindings section.

fn

The restorer function, or NULL to remove a registration.

session

A Shiny session to register the restorer for that session only, or NULL (the default) to register it globally.

Value

snap_restorer() returns fn invisibly. snap_restorers() returns a data frame with the columns name and scope ("builtin", "global", or "session").

Details

fn is called as fn(id, value, binding, session) and must return the message as a list, or NULL to skip the input (reported as skipped). It must not call update*() functions itself: those go through session$sendInputMessage(), which silently drops messages for inputs that are not on the page yet. To find the right payload, read the update*() function's source and keep the part that carries the value.

Optionally, the returned list may carry an attribute expect holding the value the binding's getValue() is expected to return after the message was applied; the client uses it to report mismatched when the widget shows something else. By default the message's value is used.

Resolution order when restoring an input: a session restorer for the id, a session restorer for its binding, a global restorer for the id or the binding, the built-in restorer for the binding, the default.

Examples

# A restorer for a hypothetical widget that expects a selected field:
snap_restorer("mypkg.myInput", function(id, value, binding, session) {
  list(selected = value)
})
snap_restorers()
#>                           name   scope
#> 1     shiny.checkboxGroupInput builtin
#> 2             shiny.radioInput builtin
#> 3            shiny.selectInput builtin
#> 4              shiny.dateInput builtin
#> 5         shiny.dateRangeInput builtin
#> 6            shiny.sliderInput builtin
#> 7          shiny.passwordInput builtin
#> 8      shiny.actionButtonInput builtin
#> 9       shiny.fileInputBinding builtin
#> 10             bslib.accordion builtin
#> 11               bslib.sidebar builtin
#> 12           bslib.task-button builtin
#> 13                  bslib.card builtin
#> 14   shinyMatrix.matrixNumeric builtin
#> 15 shinyMatrix.matrixCharacter builtin
#> 16               mypkg.myInput  global
snap_restorer("mypkg.myInput", NULL)