The panel that the viewer has open — whence

whence_opened() lets the app react when the viewer opens the panel of an output: for example, to filter other outputs to the row of a table that the viewer is looking at. Call it in a server function or a module server. It gives a reactive expression.

Usage

whence_opened(outputId, session = shiny::getDefaultReactiveDomain())

Arguments

outputId: The id of a whence output, as in the UI. In a module, give the id without the namespace, as for output$id.
session: The session. The default is the current one.

Value

A reactive expression.

Details

The reactive gives NULL while no panel of that output is open. While one is open, it gives a list:

row: the number of the row of the table, for whenceTableOutput() and whencePlotOutput(). NULL for whenceOutput(), and for the panel of a whole table.
data: that row of the table, as a data frame with one row. For whenceOutput(), the value. NULL for the panel of a whole table.

Only one panel is open at a time.

Examples

if (interactive() && requireNamespace("dplyr", quietly = TRUE)) {
  library(shiny)
  library(dplyr, warn.conflicts = FALSE)

  ui <- fluidPage(
    whenceTableOutput("by_cyl", label = "Cars by cylinders"),
    textOutput("looking_at")
  )
  server <- function(input, output, session) {
    output$by_cyl <- renderWhenceTable(
      mtcars |> group_by(cyl) |> summarise(cars = n())
    )
    opened <- whence_opened("by_cyl")
    output$looking_at <- renderText({
      req(opened())
      paste("The viewer is looking at", opened()$data$cyl, "cylinders.")
    })
  }
  shinyApp(ui, server)
}