Actions (class scene_action
) contain the functions that
are used to process a request
and determine which
ui
should be displayed. We provide five actions:
A scene can require multiple actions to be true. If you need to rely on multiple query parameters, or a cookie and a query parameter, stringing together multiple actions will probably suffice.
However, you may wish to construct more complicated actions, such as
multiple alternative query parameters (or
, not
and
), or check a request parameter that we do not support.
You can do so using construct_action()
.
Check function
Underlying each action is a check function, a
function that takes a request (and potentially other arguments), and
returns TRUE
or FALSE
.
Here we’ll implement a check for the language preferred by the user,
which is sent in the HTTP_ACCEPT_LANGUAGE
property of the
request.
We include _impl
in the name of this function to specify
that it’s the implentation function, as opposed to the main wrapper that
we’ll create below. For this we’ll just look for the supplied “language”
inside the HTTP_ACCEPT_LANGUAGE
object. In an exported
function, we’d probably more carefully parse that object.
req_accepts_language_impl <- function(request, language) {
stringr::str_detect(
tolower(request$HTTP_ACCEPT_LANGUAGE),
tolower(language)
)
}
req_accepts_language_impl(
list(HTTP_ACCEPT_LANGUAGE = "en-US,en;es-MX,es;fr-CA,fr"),
"fr"
)
#> [1] TRUE
Methods
Almost all actions will expect the GET
method. However,
it is possible for shiny apps to respond to requests using other HTTP
methods. If your action should work with a different HTTP method,
specify that in the call to the contructor.
Construct action
Construct the action using the construct_action()
function.
req_accepts_language <- function(language) {
construct_action(
fn = req_accepts_language_impl,
language = language,
# We're using the defaults for these arguments, but I'll specify them for
# clarity.
negate = FALSE,
methods = "GET"
)
}
Now you can use this action to construct scenes, just like any other action.