[英]Shiny renderUI selectInput returned NULL
I am trying to use a reactivity model with one input affecting several outputs as describe in the shiny cheat sheet. 我试图使用反应模型,其中一个输入影响几个输出,如闪亮的备忘单中所述。 I need to use renderUI because the choices list is rendered dynamically (not shown in the example) However, during initialization selectInput returns NULL rather than the default value.
我需要使用renderUI,因为选项列表是动态呈现的(示例中未显示)但是,在初始化期间,selectInput返回NULL而不是默认值。 After that first NULL value the input works as expected.
在第一个NULL值之后,输入按预期工作。 I am new to shiny and might be doing something wrong.
我是新手,可能会做错事。
UPDATE: other controls unexpectedly returned not only NULL, but also NA after initialization. 更新:其他控件意外返回不仅NULL,而且初始化后也返回NA。
See code below. 见下面的代码。 See the console output, the first input returning NULL.
查看控制台输出,第一个输入返回NULL。
Listening on http://127.0.0.1:6211
NULL
chr "1"
chr "2"
chr "1"
library(shiny)
runApp(list(
ui = bootstrapPage(
fluidPage( uiOutput('ui.A') )
),
server = function(input, output){
output$ui.A = renderUI({
selectInput("A", label = h4("input A"),
choices = list(A_1=1, A_2=2),
selected = 1)
})
A.r <- reactive({input$A })
observe({
A <- A.r()
str(A)
})
}))
Shiny has a function called observeEvent
which I almost always use instead of observer
. Shiny有一个名为
observeEvent
的函数,我几乎总是使用它而不是observer
。 It basically runs some code only when a reactive value changes, and by default it ignored NULL values. 它基本上仅在无功值更改时运行一些代码,并且默认情况下它忽略NULL值。 So here is the code to make your example work (all I had to do is change your
observe({
line to observeEvent(Ar(), {
所以这里是让你的例子工作的代码(我所要做的就是改变你的
observe({
line to observeEvent(Ar(), {
library(shiny)
runApp(list(
ui = bootstrapPage(
fluidPage( uiOutput('ui.A') )
),
server = function(input, output){
output$ui.A = renderUI({
selectInput("A", label = h4("input A"),
choices = list(A_1=1, A_2=2),
selected = 1)
})
A.r <- reactive({input$A })
observeEvent(A.r(), {
A <- A.r()
str(A)
})
}))
This might work if you use is.null() and return your "default" for input$A: 如果您使用is.null()并返回输入$ A的“默认值”,这可能会有效:
A.r <- reactive({
if(is.null(input$A)) return (1)
input$A
})
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