inst/examples/history/README.md

In GerkeLab/grkShinyThings: Reusable Shiny Modules and Other Shiny Things

This is a small demonstration of the undoHistory module.

This is a simple Shiny module for undo/redo history. The Shiny module accepts an arbitrary reactive data value. Changes in the state of this reactive value are tracked and added to the user's history. The user can then repeatedly undo and redo to walk through this stack. The module returns the currrent selected value of the reactive from this historical stack, or NULL when the app state was changed by the user.

UI

The UI undo/redo buttons are created with undoHistoryUI(). The id parameter links the undo/redo history buttons in the UI to the undo/redo history module on the server side. You can customize the appearance of the the back buttons and the fwd buttons with the _icon, _text, and _class arguments prefixed with back or fwd.

Server

On the server side, the undo/redo Shiny module is created with

undo_app_state <- undoHistory("id", value = reactive({
  # reactive inputs for historical tracking
  input$text
}))

When the user is modifying the app state, the module returns NULL. When the user is navigating the undo/redo history, the module returns the value of the most recently selected historical state.

Because this reactive can hold arbitrary data about the state of the Shiny app, it is up to the app developer to use the returned current value to update the Shiny apps' inputs and UI elements.

observe({
  req(!is.null(undo_app_state()))
  updateTextInput("text", value = undo_app_state())
})

GerkeLab/grkShinyThings documentation built on Nov. 24, 2019, 4:11 p.m.