Provide support for no_update in Dash for R

NAMESPACE

@@ -2,6 +2,7 @@
 
 S3method(print,dash_component)
 export(Dash)
+export(dashNoUpdate)
 export(input)
 export(output)
 export(state)

R/dash.R

@@ -287,11 +287,17 @@ Dash <- R6::R6Class(
  output_value <- getStackTrace(do.call(callback, callback_args),
  debug = private$debug,
  pruned_errors = private$pruned_errors)
-
+
  # reset callback context
  private$callback_context_ <- NULL
 
- if (is.null(private$stack_message)) {
+ # inspect the output_value to determine whether any outputs have no_update
+ # objects within them; these should not be updated
+ if (length(output_value) == 1 && class(output_value) == "no_update") {
+ response$body <- character(1) # return empty string
+ response$status <- 204L
+ }
+ else if (is.null(private$stack_message)) {
  # pass on output_value to encode_plotly in case there are dccGraph
  # components which include Plotly.js figures for which we'll need to 
  # run plotly_build from the plotly package

R/dependencies.R

@@ -5,11 +5,13 @@
 #' Use in conjunction with the `callback()` method from the [dash::Dash] class
 #' to define the update logic in your application.
 #'
+#' The `dashNoUpdate()` function permits application developers to prevent a
+#' single output from updating the layout. It has no formal arguments.
+#' 
 #' @name dependencies
 #' @param id a component id
 #' @param property the component property to use
 
-
 #' @rdname dependencies
 #' @export
 output <- function(id, property) {
@@ -44,3 +46,11 @@ dependency <- function(id = NULL, property = NULL) {
  property = property
  )
 }
+
+#' @rdname dependencies
+#' @export
+dashNoUpdate <- function() {
+ x <- list(NULL)
+ class(x) <- "no_update"
+ return(x)
+}

tests/integration/callbacks/test_no_update.py

@@ -0,0 +1,111 @@
+from selenium.webdriver.support.select import Select
+import time
+
+app = """
+library(dash)
+library(dashHtmlComponents)
+library(dashCoreComponents)
+
+app <- Dash$new()
+
+app$layout(
+ htmlDiv(list(
+ dccDropdown(options = list(
+ list(label = "Red", value = "#FF0000"),
+ list(label = "Green", value = "#00FF00"), 
+ list(label = "Blue", value = "#0000FF"),
+ list(label = "Do nothing", value = "nothing")
+ ),
+ id = "color-selector"),
+ htmlButton(children = "Select all the colors!",
+ id = "multi-selector"
+ ),
+ htmlDiv(id='message-box',
+ children='Please select a color choice from the dropdown menu.'),
+ htmlDiv(id='message-box2',
+ children=' ')
+ )
+ )
+)
+
+app$callback(output=list(id='message-box2', property='children'),
+ params=list(
+ input(id='multi-selector', property='n_clicks')),
+ function(n_clicks)
+ {
+ # if button has been clicked, n_clicks is numeric()
+ # on first launch of callback at layout initialization,
+ # value of n_clicks will be list(NULL), which is not
+ # comparable using >, < or =; hence the is.numeric()
+ # check
+ if (is.numeric(n_clicks) && n_clicks >= 1)
+ {
+ # return a vector to ensure that the check for
+ # class(x) == "no_update" isn't made for objects
+ # where length(x) > 1
+ return(c("Multiple color values: ", 
+ "#FF0000, ", 
+ "#00FF00, ", 
+ "#0000FF ", 
+ "returned!")
+ )
+ }
+ }
+)
+
+app$callback(output=list(id='message-box', property='children'),
+ params=list(
+ input(id='color-selector', property='value')),
+ function(color)
+ {
+ if (color %in% c("#FF0000", "#00FF00", "#0000FF")) {
+ msg <- sprintf("The hexadecimal representation of your last chosen color is %s",
+ color)
+ return(msg)
+ } else {
+ return(dashNoUpdate())
+ }
+ }
+)
+
+app$run_server()
+"""
+
+
+def test_rsnu001_no_update(dashr):
+ dashr.start_server(app)
+ dashr.find_element("#color-selector").click()
+ dashr.find_elements("div.VirtualizedSelectOption")[0].click()
+ dashr.wait_for_text_to_equal(
+ "#message-box",
+ "The hexadecimal representation of your last chosen color is #FF0000"
+ )
+ dashr.find_element("#color-selector").click()
+ dashr.find_elements("div.VirtualizedSelectOption")[3].click()
+ time.sleep(1)
+ assert dashr.find_element("#message-box").text == "The hexadecimal representation of your last chosen color is #FF0000"
+ dashr.find_element("#color-selector").click()
+ dashr.find_elements("div.VirtualizedSelectOption")[1].click()
+ dashr.wait_for_text_to_equal(
+ "#message-box",
+ "The hexadecimal representation of your last chosen color is #00FF00"
+ )
+ dashr.find_element("#color-selector").click()
+ dashr.find_elements("div.VirtualizedSelectOption")[3].click()
+ time.sleep(1)
+ assert dashr.find_element("#message-box").text == "The hexadecimal representation of your last chosen color is #00FF00"
+ dashr.find_element("#color-selector").click()
+ dashr.find_elements("div.VirtualizedSelectOption")[2].click()
+ dashr.wait_for_text_to_equal(
+ "#message-box",
+ "The hexadecimal representation of your last chosen color is #0000FF"
+ )
+ dashr.find_element("#color-selector").click()
+ dashr.find_elements("div.VirtualizedSelectOption")[3].click()
+ time.sleep(1)
+ assert dashr.find_element("#message-box").text == "The hexadecimal representation of your last chosen color is #0000FF"
+ dashr.find_element("#multi-selector").click()
+ dashr.wait_for_text_to_equal(
+ "#message-box2",
+ "Multiple color values: #FF0000, #00FF00, #0000FF returned!"
+ )

NAMESPACE

@@ -2,6 +2,7 @@
 
 S3method(print,dash_component)
 export(Dash)
+export(dashNoUpdate)
 export(input)
 export(output)
 export(state)

R/dash.R

@@ -287,11 +287,17 @@ Dash <- R6::R6Class(
  output_value <- getStackTrace(do.call(callback, callback_args),
  debug = private$debug,
  pruned_errors = private$pruned_errors)
-
+
  # reset callback context
  private$callback_context_ <- NULL
 
- if (is.null(private$stack_message)) {
+ # inspect the output_value to determine whether any outputs have no_update
+ # objects within them; these should not be updated
+ if (length(output_value) == 1 && class(output_value) == "no_update") {
+ response$body <- character(1) # return empty string
+ response$status <- 204L
+ }
+ else if (is.null(private$stack_message)) {
  # pass on output_value to encode_plotly in case there are dccGraph
  # components which include Plotly.js figures for which we'll need to 
  # run plotly_build from the plotly package

R/dependencies.R

@@ -5,11 +5,13 @@
 #' Use in conjunction with the `callback()` method from the [dash::Dash] class
 #' to define the update logic in your application.
 #'
+#' The `dashNoUpdate()` function permits application developers to prevent a
+#' single output from updating the layout. It has no formal arguments.
+#' 
 #' @name dependencies
 #' @param id a component id
 #' @param property the component property to use
 
-
 #' @rdname dependencies
 #' @export
 output <- function(id, property) {
@@ -44,3 +46,11 @@ dependency <- function(id = NULL, property = NULL) {
  property = property
  )
 }
+
+#' @rdname dependencies
+#' @export
+dashNoUpdate <- function() {
+ x <- list(NULL)
+ class(x) <- "no_update"
+ return(x)
+}

tests/integration/callbacks/test_no_update.py

@@ -0,0 +1,111 @@
+from selenium.webdriver.support.select import Select
+import time
+
+app = """
+library(dash)
+library(dashHtmlComponents)
+library(dashCoreComponents)
+
+app <- Dash$new()
+
+app$layout(
+ htmlDiv(list(
+ dccDropdown(options = list(
+ list(label = "Red", value = "#FF0000"),
+ list(label = "Green", value = "#00FF00"), 
+ list(label = "Blue", value = "#0000FF"),
+ list(label = "Do nothing", value = "nothing")
+ ),
+ id = "color-selector"),
+ htmlButton(children = "Select all the colors!",
+ id = "multi-selector"
+ ),
+ htmlDiv(id='message-box',
+ children='Please select a color choice from the dropdown menu.'),
+ htmlDiv(id='message-box2',
+ children=' ')
+ )
+ )
+)
+
+app$callback(output=list(id='message-box2', property='children'),
+ params=list(
+ input(id='multi-selector', property='n_clicks')),
+ function(n_clicks)
+ {
+ # if button has been clicked, n_clicks is numeric()
+ # on first launch of callback at layout initialization,
+ # value of n_clicks will be list(NULL), which is not
+ # comparable using >, < or =; hence the is.numeric()
+ # check
+ if (is.numeric(n_clicks) && n_clicks >= 1)
+ {
+ # return a vector to ensure that the check for
+ # class(x) == "no_update" isn't made for objects
+ # where length(x) > 1
+ return(c("Multiple color values: ", 
+ "#FF0000, ", 
+ "#00FF00, ", 
+ "#0000FF ", 
+ "returned!")
+ )
+ }
+ }
+)
+
+app$callback(output=list(id='message-box', property='children'),
+ params=list(
+ input(id='color-selector', property='value')),
+ function(color)
+ {
+ if (color %in% c("#FF0000", "#00FF00", "#0000FF")) {
+ msg <- sprintf("The hexadecimal representation of your last chosen color is %s",
+ color)
+ return(msg)
+ } else {
+ return(dashNoUpdate())
+ }
+ }
+)
+
+app$run_server()
+"""
+
+
+def test_rsnu001_no_update(dashr):
+ dashr.start_server(app)
+ dashr.find_element("#color-selector").click()
+ dashr.find_elements("div.VirtualizedSelectOption")[0].click()
+ dashr.wait_for_text_to_equal(
+ "#message-box",
+ "The hexadecimal representation of your last chosen color is #FF0000"
+ )
+ dashr.find_element("#color-selector").click()
+ dashr.find_elements("div.VirtualizedSelectOption")[3].click()
+ time.sleep(1)
+ assert dashr.find_element("#message-box").text == "The hexadecimal representation of your last chosen color is #FF0000"
+ dashr.find_element("#color-selector").click()
+ dashr.find_elements("div.VirtualizedSelectOption")[1].click()
+ dashr.wait_for_text_to_equal(
+ "#message-box",
+ "The hexadecimal representation of your last chosen color is #00FF00"
+ )
+ dashr.find_element("#color-selector").click()
+ dashr.find_elements("div.VirtualizedSelectOption")[3].click()
+ time.sleep(1)
+ assert dashr.find_element("#message-box").text == "The hexadecimal representation of your last chosen color is #00FF00"
+ dashr.find_element("#color-selector").click()
+ dashr.find_elements("div.VirtualizedSelectOption")[2].click()
+ dashr.wait_for_text_to_equal(
+ "#message-box",
+ "The hexadecimal representation of your last chosen color is #0000FF"
+ )
+ dashr.find_element("#color-selector").click()
+ dashr.find_elements("div.VirtualizedSelectOption")[3].click()
+ time.sleep(1)
+ assert dashr.find_element("#message-box").text == "The hexadecimal representation of your last chosen color is #0000FF"
+ dashr.find_element("#multi-selector").click()
+ dashr.wait_for_text_to_equal(
+ "#message-box2",
+ "Multiple color values: #FF0000, #00FF00, #0000FF returned!"
+ )

NAMESPACE

@@ -2,6 +2,7 @@
 
 S3method(print,dash_component)
 export(Dash)
+export(dashNoUpdate)
 export(input)
 export(output)
 export(state)

R/dash.R

@@ -287,11 +287,17 @@ Dash <- R6::R6Class(
  output_value <- getStackTrace(do.call(callback, callback_args),
  debug = private$debug,
  pruned_errors = private$pruned_errors)
-
+
  # reset callback context
  private$callback_context_ <- NULL
 
- if (is.null(private$stack_message)) {
+ # inspect the output_value to determine whether any outputs have no_update
+ # objects within them; these should not be updated
+ if (length(output_value) == 1 && class(output_value) == "no_update") {
+ response$body <- character(1) # return empty string
+ response$status <- 204L
+ }
+ else if (is.null(private$stack_message)) {
  # pass on output_value to encode_plotly in case there are dccGraph
  # components which include Plotly.js figures for which we'll need to 
  # run plotly_build from the plotly package

R/dependencies.R

@@ -5,11 +5,13 @@
 #' Use in conjunction with the `callback()` method from the [dash::Dash] class
 #' to define the update logic in your application.
 #'
+#' The `dashNoUpdate()` function permits application developers to prevent a
+#' single output from updating the layout. It has no formal arguments.
+#' 
 #' @name dependencies
 #' @param id a component id
 #' @param property the component property to use
 
-
 #' @rdname dependencies
 #' @export
 output <- function(id, property) {
@@ -44,3 +46,11 @@ dependency <- function(id = NULL, property = NULL) {
  property = property
  )
 }
+
+#' @rdname dependencies
+#' @export
+dashNoUpdate <- function() {
+ x <- list(NULL)
+ class(x) <- "no_update"
+ return(x)
+}

tests/integration/callbacks/test_no_update.py

@@ -0,0 +1,111 @@
+from selenium.webdriver.support.select import Select
+import time
+
+app = """
+library(dash)
+library(dashHtmlComponents)
+library(dashCoreComponents)
+
+app <- Dash$new()
+
+app$layout(
+ htmlDiv(list(
+ dccDropdown(options = list(
+ list(label = "Red", value = "#FF0000"),
+ list(label = "Green", value = "#00FF00"), 
+ list(label = "Blue", value = "#0000FF"),
+ list(label = "Do nothing", value = "nothing")
+ ),
+ id = "color-selector"),
+ htmlButton(children = "Select all the colors!",
+ id = "multi-selector"
+ ),
+ htmlDiv(id='message-box',
+ children='Please select a color choice from the dropdown menu.'),
+ htmlDiv(id='message-box2',
+ children=' ')
+ )
+ )
+)
+
+app$callback(output=list(id='message-box2', property='children'),
+ params=list(
+ input(id='multi-selector', property='n_clicks')),
+ function(n_clicks)
+ {
+ # if button has been clicked, n_clicks is numeric()
+ # on first launch of callback at layout initialization,
+ # value of n_clicks will be list(NULL), which is not
+ # comparable using >, < or =; hence the is.numeric()
+ # check
+ if (is.numeric(n_clicks) && n_clicks >= 1)
+ {
+ # return a vector to ensure that the check for
+ # class(x) == "no_update" isn't made for objects
+ # where length(x) > 1
+ return(c("Multiple color values: ", 
+ "#FF0000, ", 
+ "#00FF00, ", 
+ "#0000FF ", 
+ "returned!")
+ )
+ }
+ }
+)
+
+app$callback(output=list(id='message-box', property='children'),
+ params=list(
+ input(id='color-selector', property='value')),
+ function(color)
+ {
+ if (color %in% c("#FF0000", "#00FF00", "#0000FF")) {
+ msg <- sprintf("The hexadecimal representation of your last chosen color is %s",
+ color)
+ return(msg)
+ } else {
+ return(dashNoUpdate())
+ }
+ }
+)
+
+app$run_server()
+"""
+
+
+def test_rsnu001_no_update(dashr):
+ dashr.start_server(app)
+ dashr.find_element("#color-selector").click()
+ dashr.find_elements("div.VirtualizedSelectOption")[0].click()
+ dashr.wait_for_text_to_equal(
+ "#message-box",
+ "The hexadecimal representation of your last chosen color is #FF0000"
+ )
+ dashr.find_element("#color-selector").click()
+ dashr.find_elements("div.VirtualizedSelectOption")[3].click()
+ time.sleep(1)
+ assert dashr.find_element("#message-box").text == "The hexadecimal representation of your last chosen color is #FF0000"
+ dashr.find_element("#color-selector").click()
+ dashr.find_elements("div.VirtualizedSelectOption")[1].click()
+ dashr.wait_for_text_to_equal(
+ "#message-box",
+ "The hexadecimal representation of your last chosen color is #00FF00"
+ )
+ dashr.find_element("#color-selector").click()
+ dashr.find_elements("div.VirtualizedSelectOption")[3].click()
+ time.sleep(1)
+ assert dashr.find_element("#message-box").text == "The hexadecimal representation of your last chosen color is #00FF00"
+ dashr.find_element("#color-selector").click()
+ dashr.find_elements("div.VirtualizedSelectOption")[2].click()
+ dashr.wait_for_text_to_equal(
+ "#message-box",
+ "The hexadecimal representation of your last chosen color is #0000FF"
+ )
+ dashr.find_element("#color-selector").click()
+ dashr.find_elements("div.VirtualizedSelectOption")[3].click()
+ time.sleep(1)
+ assert dashr.find_element("#message-box").text == "The hexadecimal representation of your last chosen color is #0000FF"
+ dashr.find_element("#multi-selector").click()
+ dashr.wait_for_text_to_equal(
+ "#message-box2",
+ "Multiple color values: #FF0000, #00FF00, #0000FF returned!"
+ )

NAMESPACE

@@ -2,6 +2,7 @@
 
 S3method(print,dash_component)
 export(Dash)
+export(dashNoUpdate)
 export(input)
 export(output)
 export(state)

R/dash.R

@@ -287,11 +287,17 @@ Dash <- R6::R6Class(
  output_value <- getStackTrace(do.call(callback, callback_args),
  debug = private$debug,
  pruned_errors = private$pruned_errors)
-
+
  # reset callback context
  private$callback_context_ <- NULL
 
- if (is.null(private$stack_message)) {
+ # inspect the output_value to determine whether any outputs have no_update
+ # objects within them; these should not be updated
+ if (length(output_value) == 1 && class(output_value) == "no_update") {
+ response$body <- character(1) # return empty string
+ response$status <- 204L
+ }
+ else if (is.null(private$stack_message)) {
  # pass on output_value to encode_plotly in case there are dccGraph
  # components which include Plotly.js figures for which we'll need to 
  # run plotly_build from the plotly package

R/dependencies.R

@@ -5,11 +5,13 @@
 #' Use in conjunction with the `callback()` method from the [dash::Dash] class
 #' to define the update logic in your application.
 #'
+#' The `dashNoUpdate()` function permits application developers to prevent a
+#' single output from updating the layout. It has no formal arguments.
+#' 
 #' @name dependencies
 #' @param id a component id
 #' @param property the component property to use
 
-
 #' @rdname dependencies
 #' @export
 output <- function(id, property) {
@@ -44,3 +46,11 @@ dependency <- function(id = NULL, property = NULL) {
  property = property
  )
 }
+
+#' @rdname dependencies
+#' @export
+dashNoUpdate <- function() {
+ x <- list(NULL)
+ class(x) <- "no_update"
+ return(x)
+}

tests/integration/callbacks/test_no_update.py

@@ -0,0 +1,111 @@
+from selenium.webdriver.support.select import Select
+import time
+
+app = """
+library(dash)
+library(dashHtmlComponents)
+library(dashCoreComponents)
+
+app <- Dash$new()
+
+app$layout(
+ htmlDiv(list(
+ dccDropdown(options = list(
+ list(label = "Red", value = "#FF0000"),
+ list(label = "Green", value = "#00FF00"), 
+ list(label = "Blue", value = "#0000FF"),
+ list(label = "Do nothing", value = "nothing")
+ ),
+ id = "color-selector"),
+ htmlButton(children = "Select all the colors!",
+ id = "multi-selector"
+ ),
+ htmlDiv(id='message-box',
+ children='Please select a color choice from the dropdown menu.'),
+ htmlDiv(id='message-box2',
+ children=' ')
+ )
+ )
+)
+
+app$callback(output=list(id='message-box2', property='children'),
+ params=list(
+ input(id='multi-selector', property='n_clicks')),
+ function(n_clicks)
+ {
+ # if button has been clicked, n_clicks is numeric()
+ # on first launch of callback at layout initialization,
+ # value of n_clicks will be list(NULL), which is not
+ # comparable using >, < or =; hence the is.numeric()
+ # check
+ if (is.numeric(n_clicks) && n_clicks >= 1)
+ {
+ # return a vector to ensure that the check for
+ # class(x) == "no_update" isn't made for objects
+ # where length(x) > 1
+ return(c("Multiple color values: ", 
+ "#FF0000, ", 
+ "#00FF00, ", 
+ "#0000FF ", 
+ "returned!")
+ )
+ }
+ }
+)
+
+app$callback(output=list(id='message-box', property='children'),
+ params=list(
+ input(id='color-selector', property='value')),
+ function(color)
+ {
+ if (color %in% c("#FF0000", "#00FF00", "#0000FF")) {
+ msg <- sprintf("The hexadecimal representation of your last chosen color is %s",
+ color)
+ return(msg)
+ } else {
+ return(dashNoUpdate())
+ }
+ }
+)
+
+app$run_server()
+"""
+
+
+def test_rsnu001_no_update(dashr):
+ dashr.start_server(app)
+ dashr.find_element("#color-selector").click()
+ dashr.find_elements("div.VirtualizedSelectOption")[0].click()
+ dashr.wait_for_text_to_equal(
+ "#message-box",
+ "The hexadecimal representation of your last chosen color is #FF0000"
+ )
+ dashr.find_element("#color-selector").click()
+ dashr.find_elements("div.VirtualizedSelectOption")[3].click()
+ time.sleep(1)
+ assert dashr.find_element("#message-box").text == "The hexadecimal representation of your last chosen color is #FF0000"
+ dashr.find_element("#color-selector").click()
+ dashr.find_elements("div.VirtualizedSelectOption")[1].click()
+ dashr.wait_for_text_to_equal(
+ "#message-box",
+ "The hexadecimal representation of your last chosen color is #00FF00"
+ )
+ dashr.find_element("#color-selector").click()
+ dashr.find_elements("div.VirtualizedSelectOption")[3].click()
+ time.sleep(1)
+ assert dashr.find_element("#message-box").text == "The hexadecimal representation of your last chosen color is #00FF00"
+ dashr.find_element("#color-selector").click()
+ dashr.find_elements("div.VirtualizedSelectOption")[2].click()
+ dashr.wait_for_text_to_equal(
+ "#message-box",
+ "The hexadecimal representation of your last chosen color is #0000FF"
+ )
+ dashr.find_element("#color-selector").click()
+ dashr.find_elements("div.VirtualizedSelectOption")[3].click()
+ time.sleep(1)
+ assert dashr.find_element("#message-box").text == "The hexadecimal representation of your last chosen color is #0000FF"
+ dashr.find_element("#multi-selector").click()
+ dashr.wait_for_text_to_equal(
+ "#message-box2",
+ "Multiple color values: #FF0000, #00FF00, #0000FF returned!"
+ )

NAMESPACE

@@ -2,6 +2,7 @@
 
 S3method(print,dash_component)
 export(Dash)
+export(dashNoUpdate)
 export(input)
 export(output)
 export(state)

R/dash.R

@@ -287,11 +287,17 @@ Dash <- R6::R6Class(
  output_value <- getStackTrace(do.call(callback, callback_args),
  debug = private$debug,
  pruned_errors = private$pruned_errors)
-
+
  # reset callback context
  private$callback_context_ <- NULL
 
- if (is.null(private$stack_message)) {
+ # inspect the output_value to determine whether any outputs have no_update
+ # objects within them; these should not be updated
+ if (length(output_value) == 1 && class(output_value) == "no_update") {
+ response$body <- character(1) # return empty string
+ response$status <- 204L
+ }
+ else if (is.null(private$stack_message)) {
  # pass on output_value to encode_plotly in case there are dccGraph
  # components which include Plotly.js figures for which we'll need to 
  # run plotly_build from the plotly package

R/dependencies.R

@@ -5,11 +5,13 @@
 #' Use in conjunction with the `callback()` method from the [dash::Dash] class
 #' to define the update logic in your application.
 #'
+#' The `dashNoUpdate()` function permits application developers to prevent a
+#' single output from updating the layout. It has no formal arguments.
+#' 
 #' @name dependencies
 #' @param id a component id
 #' @param property the component property to use
 
-
 #' @rdname dependencies
 #' @export
 output <- function(id, property) {
@@ -44,3 +46,11 @@ dependency <- function(id = NULL, property = NULL) {
  property = property
  )
 }
+
+#' @rdname dependencies
+#' @export
+dashNoUpdate <- function() {
+ x <- list(NULL)
+ class(x) <- "no_update"
+ return(x)
+}

tests/integration/callbacks/test_no_update.py

@@ -0,0 +1,111 @@
+from selenium.webdriver.support.select import Select
+import time
+
+app = """
+library(dash)
+library(dashHtmlComponents)
+library(dashCoreComponents)
+
+app <- Dash$new()
+
+app$layout(
+ htmlDiv(list(
+ dccDropdown(options = list(
+ list(label = "Red", value = "#FF0000"),
+ list(label = "Green", value = "#00FF00"), 
+ list(label = "Blue", value = "#0000FF"),
+ list(label = "Do nothing", value = "nothing")
+ ),
+ id = "color-selector"),
+ htmlButton(children = "Select all the colors!",
+ id = "multi-selector"
+ ),
+ htmlDiv(id='message-box',
+ children='Please select a color choice from the dropdown menu.'),
+ htmlDiv(id='message-box2',
+ children=' ')
+ )
+ )
+)
+
+app$callback(output=list(id='message-box2', property='children'),
+ params=list(
+ input(id='multi-selector', property='n_clicks')),
+ function(n_clicks)
+ {
+ # if button has been clicked, n_clicks is numeric()
+ # on first launch of callback at layout initialization,
+ # value of n_clicks will be list(NULL), which is not
+ # comparable using >, < or =; hence the is.numeric()
+ # check
+ if (is.numeric(n_clicks) && n_clicks >= 1)
+ {
+ # return a vector to ensure that the check for
+ # class(x) == "no_update" isn't made for objects
+ # where length(x) > 1
+ return(c("Multiple color values: ", 
+ "#FF0000, ", 
+ "#00FF00, ", 
+ "#0000FF ", 
+ "returned!")
+ )
+ }
+ }
+)
+
+app$callback(output=list(id='message-box', property='children'),
+ params=list(
+ input(id='color-selector', property='value')),
+ function(color)
+ {
+ if (color %in% c("#FF0000", "#00FF00", "#0000FF")) {
+ msg <- sprintf("The hexadecimal representation of your last chosen color is %s",
+ color)
+ return(msg)
+ } else {
+ return(dashNoUpdate())
+ }
+ }
+)
+
+app$run_server()
+"""
+
+
+def test_rsnu001_no_update(dashr):
+ dashr.start_server(app)
+ dashr.find_element("#color-selector").click()
+ dashr.find_elements("div.VirtualizedSelectOption")[0].click()
+ dashr.wait_for_text_to_equal(
+ "#message-box",
+ "The hexadecimal representation of your last chosen color is #FF0000"
+ )
+ dashr.find_element("#color-selector").click()
+ dashr.find_elements("div.VirtualizedSelectOption")[3].click()
+ time.sleep(1)
+ assert dashr.find_element("#message-box").text == "The hexadecimal representation of your last chosen color is #FF0000"
+ dashr.find_element("#color-selector").click()
+ dashr.find_elements("div.VirtualizedSelectOption")[1].click()
+ dashr.wait_for_text_to_equal(
+ "#message-box",
+ "The hexadecimal representation of your last chosen color is #00FF00"
+ )
+ dashr.find_element("#color-selector").click()
+ dashr.find_elements("div.VirtualizedSelectOption")[3].click()
+ time.sleep(1)
+ assert dashr.find_element("#message-box").text == "The hexadecimal representation of your last chosen color is #00FF00"
+ dashr.find_element("#color-selector").click()
+ dashr.find_elements("div.VirtualizedSelectOption")[2].click()
+ dashr.wait_for_text_to_equal(
+ "#message-box",
+ "The hexadecimal representation of your last chosen color is #0000FF"
+ )
+ dashr.find_element("#color-selector").click()
+ dashr.find_elements("div.VirtualizedSelectOption")[3].click()
+ time.sleep(1)
+ assert dashr.find_element("#message-box").text == "The hexadecimal representation of your last chosen color is #0000FF"
+ dashr.find_element("#multi-selector").click()
+ dashr.wait_for_text_to_equal(
+ "#message-box2",
+ "Multiple color values: #FF0000, #00FF00, #0000FF returned!"
+ )

NAMESPACE

@@ -2,6 +2,7 @@
 
 S3method(print,dash_component)
 export(Dash)
+export(dashNoUpdate)
 export(input)
 export(output)
 export(state)

R/dash.R

@@ -287,11 +287,17 @@ Dash <- R6::R6Class(
  output_value <- getStackTrace(do.call(callback, callback_args),
  debug = private$debug,
  pruned_errors = private$pruned_errors)
-
+
  # reset callback context
  private$callback_context_ <- NULL
 
- if (is.null(private$stack_message)) {
+ # inspect the output_value to determine whether any outputs have no_update
+ # objects within them; these should not be updated
+ if (length(output_value) == 1 && class(output_value) == "no_update") {
+ response$body <- character(1) # return empty string
+ response$status <- 204L
+ }
+ else if (is.null(private$stack_message)) {
  # pass on output_value to encode_plotly in case there are dccGraph
  # components which include Plotly.js figures for which we'll need to 
  # run plotly_build from the plotly package

R/dependencies.R

@@ -5,11 +5,13 @@
 #' Use in conjunction with the `callback()` method from the [dash::Dash] class
 #' to define the update logic in your application.
 #'
+#' The `dashNoUpdate()` function permits application developers to prevent a
+#' single output from updating the layout. It has no formal arguments.
+#' 
 #' @name dependencies
 #' @param id a component id
 #' @param property the component property to use
 
-
 #' @rdname dependencies
 #' @export
 output <- function(id, property) {
@@ -44,3 +46,11 @@ dependency <- function(id = NULL, property = NULL) {
  property = property
  )
 }
+
+#' @rdname dependencies
+#' @export
+dashNoUpdate <- function() {
+ x <- list(NULL)
+ class(x) <- "no_update"
+ return(x)
+}

tests/integration/callbacks/test_no_update.py

@@ -0,0 +1,111 @@
+from selenium.webdriver.support.select import Select
+import time
+
+app = """
+library(dash)
+library(dashHtmlComponents)
+library(dashCoreComponents)
+
+app <- Dash$new()
+
+app$layout(
+ htmlDiv(list(
+ dccDropdown(options = list(
+ list(label = "Red", value = "#FF0000"),
+ list(label = "Green", value = "#00FF00"), 
+ list(label = "Blue", value = "#0000FF"),
+ list(label = "Do nothing", value = "nothing")
+ ),
+ id = "color-selector"),
+ htmlButton(children = "Select all the colors!",
+ id = "multi-selector"
+ ),
+ htmlDiv(id='message-box',
+ children='Please select a color choice from the dropdown menu.'),
+ htmlDiv(id='message-box2',
+ children=' ')
+ )
+ )
+)
+
+app$callback(output=list(id='message-box2', property='children'),
+ params=list(
+ input(id='multi-selector', property='n_clicks')),
+ function(n_clicks)
+ {
+ # if button has been clicked, n_clicks is numeric()
+ # on first launch of callback at layout initialization,
+ # value of n_clicks will be list(NULL), which is not
+ # comparable using >, < or =; hence the is.numeric()
+ # check
+ if (is.numeric(n_clicks) && n_clicks >= 1)
+ {
+ # return a vector to ensure that the check for
+ # class(x) == "no_update" isn't made for objects
+ # where length(x) > 1
+ return(c("Multiple color values: ", 
+ "#FF0000, ", 
+ "#00FF00, ", 
+ "#0000FF ", 
+ "returned!")
+ )
+ }
+ }
+)
+
+app$callback(output=list(id='message-box', property='children'),
+ params=list(
+ input(id='color-selector', property='value')),
+ function(color)
+ {
+ if (color %in% c("#FF0000", "#00FF00", "#0000FF")) {
+ msg <- sprintf("The hexadecimal representation of your last chosen color is %s",
+ color)
+ return(msg)
+ } else {
+ return(dashNoUpdate())
+ }
+ }
+)
+
+app$run_server()
+"""
+
+
+def test_rsnu001_no_update(dashr):
+ dashr.start_server(app)
+ dashr.find_element("#color-selector").click()
+ dashr.find_elements("div.VirtualizedSelectOption")[0].click()
+ dashr.wait_for_text_to_equal(
+ "#message-box",
+ "The hexadecimal representation of your last chosen color is #FF0000"
+ )
+ dashr.find_element("#color-selector").click()
+ dashr.find_elements("div.VirtualizedSelectOption")[3].click()
+ time.sleep(1)
+ assert dashr.find_element("#message-box").text == "The hexadecimal representation of your last chosen color is #FF0000"
+ dashr.find_element("#color-selector").click()
+ dashr.find_elements("div.VirtualizedSelectOption")[1].click()
+ dashr.wait_for_text_to_equal(
+ "#message-box",
+ "The hexadecimal representation of your last chosen color is #00FF00"
+ )
+ dashr.find_element("#color-selector").click()
+ dashr.find_elements("div.VirtualizedSelectOption")[3].click()
+ time.sleep(1)
+ assert dashr.find_element("#message-box").text == "The hexadecimal representation of your last chosen color is #00FF00"
+ dashr.find_element("#color-selector").click()
+ dashr.find_elements("div.VirtualizedSelectOption")[2].click()
+ dashr.wait_for_text_to_equal(
+ "#message-box",
+ "The hexadecimal representation of your last chosen color is #0000FF"
+ )
+ dashr.find_element("#color-selector").click()
+ dashr.find_elements("div.VirtualizedSelectOption")[3].click()
+ time.sleep(1)
+ assert dashr.find_element("#message-box").text == "The hexadecimal representation of your last chosen color is #0000FF"
+ dashr.find_element("#multi-selector").click()
+ dashr.wait_for_text_to_equal(
+ "#message-box2",
+ "Multiple color values: #FF0000, #00FF00, #0000FF returned!"
+ )

NAMESPACE

@@ -2,6 +2,7 @@
 
 S3method(print,dash_component)
 export(Dash)
+export(dashNoUpdate)
 export(input)
 export(output)
 export(state)

R/dash.R

@@ -287,11 +287,17 @@ Dash <- R6::R6Class(
  output_value <- getStackTrace(do.call(callback, callback_args),
  debug = private$debug,
  pruned_errors = private$pruned_errors)
-
+
  # reset callback context
  private$callback_context_ <- NULL
 
- if (is.null(private$stack_message)) {
+ # inspect the output_value to determine whether any outputs have no_update
+ # objects within them; these should not be updated
+ if (length(output_value) == 1 && class(output_value) == "no_update") {
+ response$body <- character(1) # return empty string
+ response$status <- 204L
+ }
+ else if (is.null(private$stack_message)) {
  # pass on output_value to encode_plotly in case there are dccGraph
  # components which include Plotly.js figures for which we'll need to 
  # run plotly_build from the plotly package

R/dependencies.R

@@ -5,11 +5,13 @@
 #' Use in conjunction with the `callback()` method from the [dash::Dash] class
 #' to define the update logic in your application.
 #'
+#' The `dashNoUpdate()` function permits application developers to prevent a
+#' single output from updating the layout. It has no formal arguments.
+#' 
 #' @name dependencies
 #' @param id a component id
 #' @param property the component property to use
 
-
 #' @rdname dependencies
 #' @export
 output <- function(id, property) {
@@ -44,3 +46,11 @@ dependency <- function(id = NULL, property = NULL) {
  property = property
  )
 }
+
+#' @rdname dependencies
+#' @export
+dashNoUpdate <- function() {
+ x <- list(NULL)
+ class(x) <- "no_update"
+ return(x)
+}

tests/integration/callbacks/test_no_update.py

@@ -0,0 +1,111 @@
+from selenium.webdriver.support.select import Select
+import time
+
+app = """
+library(dash)
+library(dashHtmlComponents)
+library(dashCoreComponents)
+
+app <- Dash$new()
+
+app$layout(
+ htmlDiv(list(
+ dccDropdown(options = list(
+ list(label = "Red", value = "#FF0000"),
+ list(label = "Green", value = "#00FF00"), 
+ list(label = "Blue", value = "#0000FF"),
+ list(label = "Do nothing", value = "nothing")
+ ),
+ id = "color-selector"),
+ htmlButton(children = "Select all the colors!",
+ id = "multi-selector"
+ ),
+ htmlDiv(id='message-box',
+ children='Please select a color choice from the dropdown menu.'),
+ htmlDiv(id='message-box2',
+ children=' ')
+ )
+ )
+)
+
+app$callback(output=list(id='message-box2', property='children'),
+ params=list(
+ input(id='multi-selector', property='n_clicks')),
+ function(n_clicks)
+ {
+ # if button has been clicked, n_clicks is numeric()
+ # on first launch of callback at layout initialization,
+ # value of n_clicks will be list(NULL), which is not
+ # comparable using >, < or =; hence the is.numeric()
+ # check
+ if (is.numeric(n_clicks) && n_clicks >= 1)
+ {
+ # return a vector to ensure that the check for
+ # class(x) == "no_update" isn't made for objects
+ # where length(x) > 1
+ return(c("Multiple color values: ", 
+ "#FF0000, ", 
+ "#00FF00, ", 
+ "#0000FF ", 
+ "returned!")
+ )
+ }
+ }
+)
+
+app$callback(output=list(id='message-box', property='children'),
+ params=list(
+ input(id='color-selector', property='value')),
+ function(color)
+ {
+ if (color %in% c("#FF0000", "#00FF00", "#0000FF")) {
+ msg <- sprintf("The hexadecimal representation of your last chosen color is %s",
+ color)
+ return(msg)
+ } else {
+ return(dashNoUpdate())
+ }
+ }
+)
+
+app$run_server()
+"""
+
+
+def test_rsnu001_no_update(dashr):
+ dashr.start_server(app)
+ dashr.find_element("#color-selector").click()
+ dashr.find_elements("div.VirtualizedSelectOption")[0].click()
+ dashr.wait_for_text_to_equal(
+ "#message-box",
+ "The hexadecimal representation of your last chosen color is #FF0000"
+ )
+ dashr.find_element("#color-selector").click()
+ dashr.find_elements("div.VirtualizedSelectOption")[3].click()
+ time.sleep(1)
+ assert dashr.find_element("#message-box").text == "The hexadecimal representation of your last chosen color is #FF0000"
+ dashr.find_element("#color-selector").click()
+ dashr.find_elements("div.VirtualizedSelectOption")[1].click()
+ dashr.wait_for_text_to_equal(
+ "#message-box",
+ "The hexadecimal representation of your last chosen color is #00FF00"
+ )
+ dashr.find_element("#color-selector").click()
+ dashr.find_elements("div.VirtualizedSelectOption")[3].click()
+ time.sleep(1)
+ assert dashr.find_element("#message-box").text == "The hexadecimal representation of your last chosen color is #00FF00"
+ dashr.find_element("#color-selector").click()
+ dashr.find_elements("div.VirtualizedSelectOption")[2].click()
+ dashr.wait_for_text_to_equal(
+ "#message-box",
+ "The hexadecimal representation of your last chosen color is #0000FF"
+ )
+ dashr.find_element("#color-selector").click()
+ dashr.find_elements("div.VirtualizedSelectOption")[3].click()
+ time.sleep(1)
+ assert dashr.find_element("#message-box").text == "The hexadecimal representation of your last chosen color is #0000FF"
+ dashr.find_element("#multi-selector").click()
+ dashr.wait_for_text_to_equal(
+ "#message-box2",
+ "Multiple color values: #FF0000, #00FF00, #0000FF returned!"
+ )