Package 'scenes'

Choose Between Scenes

Description

Specify a function that uses actions and the request object to choose which Shiny UI to serve.

Usage

change_scene(..., fall_through = default_ui)

Arguments

...	One or more shiny_scenes.
fall_through	A ui to display if no scenes are valid. The default value, default_ui(), returns an HTTP 422 status code indicating that the request cannot be processed.

Value

A function that processes the request object to deliver a Shiny ui.

Examples

scene1 <- set_scene(
  "A shiny ui",
  req_has_query("scene", 1)
)
scene2 <- set_scene(
  "Another shiny ui",
  req_has_query("scene", 2)
)

ui <- change_scene(
  scene1,
  scene2
)
ui

---

Construct a Scene Action

Description

Generate the check function for an action, and use it to create a scene_action object.

Usage

construct_action(fn, ..., negate = FALSE, methods = "GET")

Arguments

fn	A function that takes a request (and potentially other arguments) and returns TRUE or FALSE.
...	Additional parameters passed on to fn.
negate	If TRUE, trigger the corresponding scene when this action is not matched.
methods	The http methods which needs to be accepted in order for this function to make sense. Default "GET" should work in almost all cases.

Value

A scene_action.

Examples

simple_function <- function(request) {
  !missing(request) && length(request) > 0
}
sample_action <- construct_action(simple_function)
sample_action$check_fn()
sample_action$check_fn(list())
sample_action$check_fn(list(a = 1))

---

Default UI for Unprocessable Requests

Description

A plain text UI that returns an HTTP status of 422, indicating that the request was well-formed, but semantically incorrect.

Usage

default_ui()

Value

A plain text UI with status code 422.

Examples

default_ui()

---

Switch Scenes on Cookies

Description

Create a scene_action specifying a cookie that must be present (or absent) and optionally a check function for that cookie.

Usage

req_has_cookie(cookie_name, validation_fn = NULL, ..., negate = FALSE)

Arguments

cookie_name	The cookie that must be present, as a length-1 character vector.
validation_fn	A function that takes the value of the cookie as the first parameter, and returns TRUE if the cookie is valid, and FALSE otherwise.
...	Additional parameters passed on to validation_fn.
negate	If TRUE, trigger the corresponding scene when this action is not matched.

Value

A scene_action, to be used in set_scene().

Examples

# Specify an action to detect a cookie named "mycookie".
req_has_cookie("mycookie")

# Specify an action to detect the *lack* of a cookie named "mycookie".
req_has_cookie("mycookie", negate = TRUE)

# Specify an action to detect a cookie named "mycookie" that has 27
# characters.
req_has_cookie(
  cookie_name = "mycookie",
  validation_fn = function(cookie_value) {
    nchar(cookie_value == 27)
  }
)

# Specify an action to detect a cookie named "mycookie" that has a
# variable-defined number of characters.
expect_n_chars <- function(x, N) {
  nchar(x) == N
}
my_N <- 27 # Perhaps set by an environment variable.
req_has_cookie(
  cookie_name = "mycookie",
  validation_fn = expect_n_chars,
  N = my_N
)

---

Switch Scenes on Query

Description

Create a scene_action specifying a key that must be present (or absent) in the query string (the part of the URL when the shiny app was called, after "?"), and optionally a value or values for that key. For example, in myapps.shinyapps.io/myapp?param1=1&param2=text, ?param1=1&param2=text is the query string, param1 and param2 are keys, and 1 and text are their corresponding values.

Usage

req_has_query(key, values = NULL, negate = FALSE)

Arguments

key	The key that must be present, as a length-1 character vector.
values	Details about what to look for in the key. NULL indicates that the key must be present but its contents are unimportant for this action. Otherwise the actual value of the query must be present in values.
negate	If TRUE, trigger the corresponding scene when this action is not matched.

Value

A scene_action, to be used in set_scene().

Examples

# Specify an action to detect a "code" parameter in the query.
req_has_query("code")

# Specify an action to detect the *lack* of a "code" parameter in the query.
req_has_query("code", negate = TRUE)

# Specify an action to detect a "language" parameter, with values containing
# "en" or "es".
req_has_query("language", "en|es")

---

Switch Scenes on Method

Description

Create a scene_action specifying the HTTP method that must be used (or not used).

Usage

req_uses_method(method, negate = FALSE)

req_uses_get(negate = FALSE)

req_uses_post(negate = FALSE)

Arguments

method	The expected HTTP method.
negate	If TRUE, trigger the corresponding scene when this action is not matched.

Value

A scene_action, to be used in set_scene().

Examples

req_uses_method("GET")
req_uses_method("POST")
req_uses_get()
req_uses_get(negate = TRUE)
req_uses_post()
req_uses_post(negate = TRUE)

---

scene_action class

Description

A scene_action object is a list with components check_fn and methods. It is used to test whether a request should trigger a particlar scene.

See Also

construct_action()

---

Link a UI to Required Actions

Description

Define a shiny_scene by linking a UI to zero or more scene_action requirements.

Usage

set_scene(ui, ...)

Arguments

ui	A shiny ui.
...	Zero or more scene_actions.

Value

A shiny_scene.

Examples

scene1 <- set_scene(
  "A shiny ui",
  req_has_query("scene", 1)
)
scene1
scene2 <- set_scene(
  "Another shiny ui",
  req_has_query("scene", 2)
)
scene2

---

shiny_scene class

Description

A shiny_scene object is a list with components ui and actions. It is used to define what should display in a Shiny app in different scenarios.

See Also

set_scene()

---