Shiny: runExample gives error (Can't call `runApp()` from within `runApp()`)

Question

I'm using rmarkdown (1.4) / knitr (1.15.1) in Rstudio to create an R markdown HTML page. I'm incorporating shiny into the file to make an interactive doc (via runtime: shiny).

When I try to run an example from Shiny, I get an error:

```{r, eval=TRUE,chunk_title='Shiny_Example'}
runExample("01_hello")
```

Error: can't call runApp() from within runApp(). If your application code contains runApp(), please remove it.

If I run the code outside of an R markdown code chunk, I can get the app to load just fine (even in the same session of Rstudio).

I did notice that the runExample code uses runApp and not shinyapp.

Is this the root of my problem? Or am I possibly doing something else wrong??

---

My Code:

---
title: "Shiny Not Working"
output: html_document
runtime: shiny
---

```{r, eval=TRUE,chunk_title='Shiny_Example'}
library(shiny)
runExample("01_hello")
```

Full Error w/ Stack Trace:

Warning: Error in runApp: Can't call `runApp()` from within `runApp()`. 
If your application code contains `runApp()`, please remove it.

Stack trace (innermost first):
117: runApp
116: runExample
115: eval
114: eval
113: withVisible
112: withCallingHandlers
111: handle
110: timing_fn
109: evaluate_call
108: evaluate::evaluate
107: evaluate
106: in_dir
105: block_exec
104: call_block
103: process_group.block
102: process_group
101: withCallingHandlers
100: process_file
 99: knitr::knit
 98: <Anonymous>
 97: do.call
 96: contextFunc
 95: .getReactiveEnvironment()$runWith
 94: shiny::maskReactiveContext
 93: <reactive>
 82: doc
 81: shiny::renderUI
 80: func
 79: origRenderFunc
 78: output$__reactivedoc__
  3: <Anonymous>
  2: do.call
  1: rmarkdown::run

Also Note:

Running other shiny code works fine with this set-up:

---
title: "Shiny Not Working"
output: html_document
runtime: shiny
---

```{r, eval=TRUE,chunk_title='Simple_Shiny'}
library(shiny)
ui <- fluidPage()
server <- function(input, output){}
shinyApp(ui = ui, server = server)
```

---

sessionInfo of note:

R version 3.3.2 (2016-10-31)
Platform: x86_64-w64-mingw32/x64 (64-bit)
Running under: Windows 7 x64 (build 7601) Service Pack 1

shiny_1.0.1  rmarkdown_1.4  knitr_1.15.1

Answer 1

So I found a workaround solution (which I'll detail below).

However, I would still like to know why the runExample code doesn't work (i.e., is this a bug??) and whether there is a more official/proper way to go about making it work.

My solution:

Change the function in runExample from runApp() to shinyAppDir().

Original runExample code:

function (example = NA, port = NULL, launch.browser = getOption("shiny.launch.browser", 
    interactive()), host = getOption("shiny.host", "127.0.0.1"), 
    display.mode = c("auto", "normal", "showcase")) 
{
    examplesDir <- system.file("examples", package = "shiny")
    dir <- resolve(examplesDir, example)
    if (is.null(dir)) {
        if (is.na(example)) {
            errFun <- message
            errMsg <- ""
        }
        else {
            errFun <- stop
            errMsg <- paste("Example", example, "does not exist. ")
        }
        errFun(errMsg, "Valid examples are \"", paste(list.files(examplesDir), 
            collapse = "\", \""), "\"")
    }
    else {
        runApp(dir, port = port, host = host, launch.browser = launch.browser, 
            display.mode = display.mode)
    }
}

My edited code:

(note: change in final internal function to shinyAppDir)

runExample2 <- function (example = NA, port = NULL, launch.browser = getOption("shiny.launch.browser", 
    interactive()), host = getOption("shiny.host", "127.0.0.1"), 
    display.mode = c("auto", "normal", "showcase")) 
{
    examplesDir <- system.file("examples", package = "shiny")
    dir <- resolve(examplesDir, example)
    if (is.null(dir)) {
        if (is.na(example)) {
            errFun <- message
            errMsg <- ""
        }
        else {
            errFun <- stop
            errMsg <- paste("Example", example, "does not exist. ")
        }
        errFun(errMsg, "Valid examples are \"", paste(list.files(examplesDir), 
            collapse = "\", \""), "\"")
    }
    else {
        shinyAppDir(appDir = dir)
    }
}

I realize I've lost the ability to apply port, host, launch.browser, and display.mode arguments to my modified function (though I left that code in for comparison sake), but I've traded that for a working solution.

^{Note: for some reason neither resolve() nor resolve's internal function isWindows() was recognized by my machine (i.e., I got the error Error: could not find function "resolve"), so I used getAnywhere() to find the code and then assigned these functions manually before creating runExample2.}

---

My full WORKING r markdown code:

---
title: "Shiny Not working"
date: "Today"
output: html_document
runtime: shiny
--- 


```{r, eval=TRUE,chunk_title='Shiny_Example'}
library(shiny)

isWindows <- function () 
.Platform$OS.type == "windows"

resolve <- function (dir, relpath) 
{
    abs.path <- file.path(dir, relpath)
    if (!file.exists(abs.path)) 
        return(NULL)
    abs.path <- normalizePath(abs.path, winslash = "/", mustWork = TRUE)
    dir <- normalizePath(dir, winslash = "/", mustWork = TRUE)
    if (isWindows()) 
        dir <- sub("/$", "", dir)
    if (nchar(abs.path) <= nchar(dir) + 1) 
        return(NULL)
    if (substr(abs.path, 1, nchar(dir)) != dir || substr(abs.path, 
        nchar(dir) + 1, nchar(dir) + 1) != "/") {
        return(NULL)
    }
    return(abs.path)
}


runExample2 <- function (example = NA, port = NULL, launch.browser = getOption("shiny.launch.browser", 
    interactive()), host = getOption("shiny.host", "127.0.0.1"), 
    display.mode = c("auto", "normal", "showcase")) 
{
    examplesDir <- system.file("examples", package = "shiny")
    dir <- resolve(examplesDir, example)
    if (is.null(dir)) {
        if (is.na(example)) {
            errFun <- message
            errMsg <- ""
        }
        else {
            errFun <- stop
            errMsg <- paste("Example", example, "does not exist. ")
        }
        errFun(errMsg, "Valid examples are \"", paste(list.files(examplesDir), 
            collapse = "\", \""), "\"")
    }
    else {
        shinyAppDir(appDir = dir
)
    }
}


runExample2("01_hello")
```