R Shiny：conditionalPanel具有基于textInput的条件（操作方法）

Question

I would like to use a conditionPanel that would appear only if a preceding textInput has been completed (the initial value of it being ""). What is the right way to define the condition in the conditionalPanel correctly. Here is a reproducible code:

ui <- pageWithSidebar(
headerPanel("TEST"),
sidebarPanel(
textInput('test', "","")),

mainPanel(               
conditionalPanel(condition = "input.test != "" ", #problem is here. I've tried many possibilities (such as input.test > 0) but none have worked
                 helpText("abc"))
)
)

server <- function(input,output){ 
}

runApp(list(ui=ui,server=server))

Any advice/suggestion would be greatly appreciated !

Cheers

Answer 1

As noted in the comments, changing the condition to "input.test != ''" or 'input.test != ""' works as it deals with the issue of having quotes within quotes.

The other solution is to change the condition to "input.test.length > 0" which works because if you look at the source code for conditionalPanel (below) it's just creating a div where the data-display-if attribute is the condition. Considering its going straight to html it was a good guess that using js for the condition would work.

And I could have just read the docs... From ?conditionalPanel :

condition: A JavaScript expression that will be evaluated repeatedly to
          determine whether the panel should be displayed.

conditionalPanel
function (condition, ...) 
{
    div(`data-display-if` = condition, ...)
}