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Communication

Introduction

Basically, communication to the module server relies on the server function arguments and UI-Server interactions, while communication from the module server (to its parent) relies on the server function return value(s).

Note

The framework communication strategy has been implemented based on the research & exploration work captured in this eBook: Communication between shiny modules.

It is expected that the package will be used in this context.

Arguments

Among the arguments that can be passed to the server function to tune its internal behaviors are the reactive parameters named trigger & filter that behave like event managers.

Whenever they receive a reactive object reference as input value, the module will take a dependency on it and declare a listener to react to specific events for the module to execute dedicated actions on the items.

  • trigger is used to pass create / update / delete actions

  • filter is used to set / unset filters

Reactive arguments are a key feature for the module to be used within more advanced implementations.

Return value(s)

The module server function returns a list of elements that are accessible outside the module.

Among these elements are reactive object’s references that are used as communication objects. You can take a dependency / listen to those objects to trigger further actions in your app.

A typical example is a plot that will be updated as soon as the items are modified.

# -- call the module server
mydata <- kitems::kitems(id = "my_data", path = "./data")

# -- plot
output$plot <- renderPlot({
  
  # -- do something here
  
}) |> bindEvent(mydata$items())

Considerations

The magic with passing references is that the value itself is not copied or duplicated.1

All the reactive objects of the return value are created with the shiny::reactive() function, so that it is not possible to update them from outside of the module server function.

It makes the framework more robust against data model or item corruption.

It also allows to use the exported functions of the package from outside of the module server, which provides more flexible implementation options.