inst/examples/history/app.R

In gadenbuie/shinyThings: Reusable Shiny Modules and Other Shiny Things

library(shiny)
library(shinyThings)

ui <- fluidPage(
  tags$head(tags$style(HTML("body { margin: 1em auto; max-width: 600px; }"))),
  # Add the Undo/Redo buttons to the UI
  undoHistoryUI("hist", back_text = "Step Backward", fwd_text = "Step Forward"),

  # A simple text input element whose history we'll track
  textInput("text", "Enter your text here"),

  # Debugging elements for the demo
  verbatimTextOutput("v"),
  tags$h4("Debug"),
  tags$p(
    "You can enable the debug view by including",
    tags$code("undoHistoryUI_debug('module_id')"),
    "in your UI. It shows the undo history stack, the current selected state,",
    "if the user moves backward or forward in the stack, and the \"future\"",
    "states if the user can step forward."
  ),
  undoHistoryUI_debug("hist")
)

server <- function(input, output, session) {
  # Use undoHistory() to keep track of the value of input$text
  undo_app_state <- undoHistory(
    id = "hist",
    value = reactive({
      # Value must be a reactive, but can be any structure you want
      req(!is.null(input$text))
      input$text
    })
  )

  # Use an observer to receive updates from undoHistory() and update the app.
  observe({
    req(!is.null(undo_app_state())) #<< Need to update app whenever not NULL

    # Manually update app UI and reactive values
    updateTextInput(session, "text", value = undo_app_state())
  })

  # Just for debugging
  output$v <- renderPrint(input$text)
}

shinyApp(ui, server)