英文:
Equivalent observers in Shiny apps but different behaviors
问题
以下是翻译好的部分：
第一个Shiny应用与第二个Shiny应用之间的区别在于，第一个应用包括以下代码：
observeEvent(
input$alert,
{
flag(TRUE)
}
)
而在第二个应用中，这段代码被以下代码替代：
observeEvent(
list(input$alert, input$X),
{
flag(TRUE)
}, ignoreInit = TRUE
)
其中 input$X 始终为 NULL。
然而，这两个应用的行为不同（多次单击按钮会产生不同效果）。为什么？我不理解第二个应用的行为。
英文:
The difference between the two Shiny apps is that the first one includes
observeEvent(
input$alert,
{
flag(TRUE)
}
)
while this code is replaced with the following code in the second one:
observeEvent(
list(input$alert, input$X),
{
flag(TRUE)
}, ignoreInit = TRUE
)
where input$X is always NULL.
However the two apps have a different behavior (click several times on the button). Why? I don't understand the behavior of the second one.
library(shiny)
library(shinyWidgets)
ui <- fluidPage(
mainPanel(
actionButton(
inputId = "button",
label = "ALERT"
)
)
)
server1 <- function(input, output, session) {
flag <- reactiveVal(NULL)
observeEvent(
input$button,
{
confirmSweetAlert(
inputId = "alert",
title = "ALERT",
type = "error"
)
}
)
observeEvent(
input$alert,
{
flag(TRUE)
}
)
observeEvent(
flag(),
{
flag(NULL)
sendSweetAlert(
title = "ALERT 2",
type = "error"
)
}
)
}
server2 <- function(input, output, session) {
flag <- reactiveVal(NULL)
observeEvent(
input$button,
{
confirmSweetAlert(
inputId = "alert",
title = "ALERT",
type = "error"
)
}
)
observeEvent(
list(input$alert, input$X),
{
flag(TRUE)
}, ignoreInit = TRUE
)
observeEvent(
flag(),
{
flag(NULL)
sendSweetAlert(
title = "ALERT 2",
type = "error"
)
}
)
}
shinyApp(ui = ui, server = server1)
shinyApp(ui = ui, server = server2)
答案1
得分: 1
以下是您要翻译的部分：
"The different behaviour is caused by the fact, that list(NULL, NULL) is not NULL (resulting in flag being set to TRUE):
> is.null(list(NULL, NULL))
[1] FALSE
and observeEvent uses ignoreNULL = TRUE by default.
Setting ignoreNULL = FALSE in server1 results in the same behaviour as shown for server2:
server1 <- function(input, output, session) {
flag <- reactiveVal(NULL)
observeEvent(
input$button,
{
confirmSweetAlert(
inputId = "alert",
title = "ALERT",
type = "error"
)
}
)
observeEvent(
input$alert,
{
flag(TRUE)
}, ignoreNULL = FALSE
)
observeEvent(
flag(),
{
flag(NULL)
sendSweetAlert(
title = "ALERT 2",
type = "error"
)
}
)
}
As an alternative use c(input$alert, input$X) instead of list(input$alert, input$X) in server2:
> is.null(c(NULL, NULL))
[1] TRUE
server2 <- function(input, output, session) {
flag <- reactiveVal(NULL)
observeEvent(input$button,
{
confirmSweetAlert(
inputId = "alert",
title = "ALERT",
type = "error"
)
}
)
observeEvent({c(input$alert, input$X)},
{
flag(TRUE)
}, ignoreInit = TRUE
)
observeEvent(
flag(),
{
flag(NULL)
sendSweetAlert(
title = "ALERT 2",
type = "error"
)
}
)
}
英文:
The different behaviour is caused by the fact, that list(NULL, NULL) is not NULL (resulting in flag being set to TRUE):
> is.null(list(NULL, NULL))
[1] FALSE
and observeEvent uses ignoreNULL = TRUE by default.
Setting ignoreNULL = FALSE in server1 results in the same behaviour as shown for server2:
server1 <- function(input, output, session) {
flag <- reactiveVal(NULL)
observeEvent(
input$button,
{
confirmSweetAlert(
inputId = "alert",
title = "ALERT",
type = "error"
)
}
)
observeEvent(
input$alert,
{
flag(TRUE)
}, ignoreNULL = FALSE
)
observeEvent(
flag(),
{
flag(NULL)
sendSweetAlert(
title = "ALERT 2",
type = "error"
)
}
)
}
As an alternative use c(input$alert, input$X) instead of list(input$alert, input$X) in server2:
> is.null(c(NULL, NULL))
[1] TRUE
server2 <- function(input, output, session) {
flag <- reactiveVal(NULL)
observeEvent(input$button,
{
confirmSweetAlert(
inputId = "alert",
title = "ALERT",
type = "error"
)
}
)
observeEvent({c(input$alert, input$X)},
{
flag(TRUE)
}, ignoreInit = TRUE
)
observeEvent(
flag(),
{
flag(NULL)
sendSweetAlert(
title = "ALERT 2",
type = "error"
)
}
)
}
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