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Provide support for no_update in Dash for R #111

Merged
merged 12 commits into from
Aug 13, 2019
1 change: 1 addition & 0 deletions NAMESPACE
Original file line number Diff line number Diff line change
Expand Up @@ -2,6 +2,7 @@

S3method(print,dash_component)
export(Dash)
export(dashNoUpdate)
export(input)
export(output)
export(state)
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10 changes: 8 additions & 2 deletions R/dash.R
Original file line number Diff line number Diff line change
Expand Up @@ -287,11 +287,17 @@ Dash <- R6::R6Class(
output_value <- getStackTrace(do.call(callback, callback_args),
debug = private$debug,
pruned_errors = private$pruned_errors)

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# reset callback context
private$callback_context_ <- NULL

if (is.null(private$stack_message)) {
# inspect the output_value to determine whether any outputs have no_update
# objects within them; these should not be updated
if (length(output_value) == 1 && class(output_value) == "no_update") {
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response$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
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14 changes: 13 additions & 1 deletion R/dependencies.R
Original file line number Diff line number Diff line change
Expand Up @@ -5,11 +5,15 @@
#' 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, but
#' returns an object of class `no_update`, for which Dash will return a `204`
#' status code and empty response body.
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#'
#' @name dependencies
#' @param id a component id
#' @param property the component property to use


#' @rdname dependencies
#' @export
output <- function(id, property) {
Expand Down Expand Up @@ -44,3 +48,11 @@ dependency <- function(id = NULL, property = NULL) {
property = property
)
}

#' @rdname dependencies
#' @export
dashNoUpdate <- function() {
x <- list(NULL)
class(x) <- "no_update"
return(x)
}
9 changes: 9 additions & 0 deletions man/dependencies.Rd

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63 changes: 63 additions & 0 deletions tests/integration/callbacks/test_no_update.py
Original file line number Diff line number Diff line change
@@ -0,0 +1,63 @@
from selenium.webdriver.support.select import Select

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"),
htmlDiv(id='message-box',
children='Please select a colour choice from the dropdown menu.')
)
)
)

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 colour 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()
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dashr.find_elements("div.VirtualizedSelectOption")[0].click()
assert dashr.find_element("#message-box").text == "The hexadecimal representation of your last chosen colour is #FF0000"
dashr.find_element("#color-selector").click()
dashr.find_elements("div.VirtualizedSelectOption")[3].click()
assert dashr.find_element("#message-box").text == "The hexadecimal representation of your last chosen colour is #FF0000"
dashr.find_element("#color-selector").click()
dashr.find_elements("div.VirtualizedSelectOption")[1].click()
assert dashr.find_element("#message-box").text == "The hexadecimal representation of your last chosen colour is #00FF00"
dashr.find_element("#color-selector").click()
dashr.find_elements("div.VirtualizedSelectOption")[3].click()
assert dashr.find_element("#message-box").text == "The hexadecimal representation of your last chosen colour is #00FF00"
dashr.find_element("#color-selector").click()
dashr.find_elements("div.VirtualizedSelectOption")[2].click()
assert dashr.find_element("#message-box").text == "The hexadecimal representation of your last chosen colour is #0000FF"
dashr.find_element("#color-selector").click()
dashr.find_elements("div.VirtualizedSelectOption")[3].click()
assert dashr.find_element("#message-box").text == "The hexadecimal representation of your last chosen colour is #0000FF"