launch.qmd

# Launch {#sec-launch}

```{r}
#| eval: true 
#| echo: false 
#| include: false
source("_common.R")
```

```{r}
#| label: co_box_tldr
#| echo: false
#| results: asis
#| eval: true
co_box(
  color = "b", 
  look = "default", hsize = "1.10", size = "1.05",
  header = "TLDR: Launching your app", fold = TRUE,
  contents = "
**Launching Apps:** 
  
- **`shinyApp()`**: can be bundled in a standalone app function to store an app-package\n
    - Also useful for quick prototyping or if an app is in a single `.R` script\n
    - Returns a shiny app object (helpful with testing)\n
  
- **`runApp()`**: versatile function that can launch apps in multiple formats/locations\n
    - A directory with a `server.R` and `ui.R`, or a single `app.R` file`\n
    - An app object created by `shinyApp()`\n
  
- **`shinyAppDir()`**: useful if you need launch a Shiny app programmatically from a directory.\n
"
)
```

---

This chapter covers the differences between `shinyApp()`, `runApp()`, and `shinyAppDir()`, what should go in an `app.R` file, and other options for launching an app (or apps) from within an app-package.

```{r}
#| label: co_box_positron_version
#| echo: false
#| results: asis
#| eval: true
co_box(
  color = "b", 
  look = "simple", 
  hsize = "1.10", 
  size = "1.05",
  header = "![](images/positron.png){height=20} Positron Version", 
  fold = TRUE,
  contents = "At the time of this writing, the [2024.09.0-1](https://github.com/posit-dev/positron/releases/tag/2024.09.0-1) pre-release of Positron was available for testing."
)
```


During development, we have a variety of options for launching applications. Both RStudio ![](images/rstudio-icon.png){height=20} and Positron ![](images/positron.png){height=20} offer a single-click button to run our application the top of the **Source** pane/**Editor**. We can also launch the app by calling the standalone app function in the **Console**. Below we'll cover what happens behind the scenes when we click on these icons.

:::: {.callout-tip collapse='true' appearance='default'}

## [Accessing the code examples]{style='font-weight: bold; font-size: 1.15em;'}

::: {style='font-size: 0.95em; color: #282b2d;'}

I've created the [`shinypak` R package](https://mjfrigaard.github.io/shinypak/) In an effort to make each section accessible and easy to follow:
  
Install `shinypak` using `pak` (or `remotes`):

```{r}
#| code-fold: false 
#| message: false
#| warning: false
#| eval: false
# install.packages('pak')
pak::pak('mjfrigaard/shinypak')
```

Review the chapters in each section:
  
```{r}
#| code-fold: false 
#| message: false
#| warning: false
#| collapse: true
library(shinypak)
list_apps(regex = '^08')
```

Launch an app: 

```{r}
#| code-fold: false 
#| eval: false
launch(app = "08_launch-app")
```

::: 

::::


## 'Running' apps

In the current branch of `sap`, the `app.R` file contains a call to `launch_app()`, which loads the package and passes the UI and server functions to `shinyApp()`.

```{r}
#| label: git_margin_box_06.2_pkg-imports
#| echo: false
#| results: asis
#| eval: true
git_margin_box(
  contents = "standard",
  fig_pw = '75%', 
  branch = "06.2_pkg-imports", 
  repo = 'sap')
```

As we can see in the image below, this places the **Run App** icon in RStudio's ![](images/rstudio-icon.png){height=20} **Source** pane. In Positron ![](images/positron.png){height=20}, the `app.R` file displays the **Run Shiny App**.

::: {.panel-tabset}

### RStudio ![](images/rstudio-icon.png){height=20}

![](images/launch_run_app_from_imports.png){width=100%}

### Positron ![](images/positron.png){height=20}

![](images/launch_positron_run_app.png){width=100%}

:::

Clicking on either **Run App**/**Run Shiny App** buttons calls `runApp()` and launches our application, but with a `loadSupport()` warning. 

```{r}
#| label: co_box_load_support_warn
#| echo: false
#| results: asis
#| eval: true
co_box(
  color = "r", 
  look = "default", 
  hsize = "1.10", 
  size = "1.05", 
  fold = TRUE,
  header = "loadSupport() warning",
  contents = "
<br>

![](images/launch_loadsupport_error_run_app.png){width=100%}
  
The warning in the **Console** is telling us `loadSupport()` has detected that `sap` is a package, but it's still sourcing the `R/` subdirectory.[^load-support-shiny-chap]

[^load-support-shiny-chap]: If you recall, we covered the  [`loadSupport()`](https://shiny.posit.co/r/reference/shiny/1.5.0/loadsupport) function in [Chapter 2](shiny.qmd).

")
```

The section below will cover the `loadSupport()` warning and why it appears when using the **Run App**/**Run Shiny App** buttons in RStudio ![](images/rstudio-icon.png){height=20} and Positron ![](images/positron.png){height=20}.

### [`loadSupport()`]{style="font-size: 0.95em; font-weight: bold;"} warnings

```{r}
#| label: co_box_terminology
#| echo: false
#| results: asis
#| eval: true
co_box(
  color = "b", 
  look = "default", 
  fold = FALSE,
  hsize = "1.10", 
  size = "1.05", 
  header = "'Launch' vs. 'Run'",
  contents = "
I'll be using the term 'launch' to differentiate successfully displaying the application locally (either in the IDE window, viewer pane, or browser) from clicking on the **Run App**/**Run Shiny App** button or calling the `runApp()` function."
)
```





::: {.panel-tabset}

### RStudio ![](images/rstudio-icon.png){height=20}

As noted above, clicking **Run App** in RStudio ![](images/rstudio-icon.png){height=20} calls `runApp()` and launches our application with a `loadSupport()` warning printed in the **Console**.

![Clicking **Run App** in RStudio calls `runApp()` and displays the `loadSupport()` warning](images/launch_loadsupport_error.png){width=100%}

### Positron ![](images/positron.png){height=20}

In Positron ![](images/positron.png){height=20}, clicking on the **Run Shiny App** button launches the application with a slightly different process than RStudio ![](images/rstudio-icon.png){height=20}:

![Clicking **Run Shiny App** in Positron calls `runApp()` and displays the `loadSupport()` warning](images/launch_positron_Run_Shiny_App.png){width=100%}

1. A new Shiny terminal process is started with the `--devmode` option   
2. `runApp()` is called with the *full* path to our `app.R` file and a `port` argument[^positron-browser]  
3. The `loadSupport()` warning is displayed in the Terminal

[^positron-browser]: I've displayed the application in the browser clicking on the ![](images/launch_positron_shiny_popout.png){height=20} 'Open the current URL in the default browser' icon.

:::

-------------------------------------------------

It's important to note that we also see the `loadSupport()` warning if we bypass the **Run App**/**Run Shiny App** buttons and call `shiny::runApp()` directly in the **Console**:

::: {.panel-tabset}

### RStudio ![](images/rstudio-icon.png){height=20}

![Calling `runApp()` directly in RStudio's **Console** displays the `loadSupport()` warning](images/launch_rstudio_runApp.png)

### Positron ![](images/positron.png){height=20}

![Calling `runApp()` directly in Positron's **Console** displays the `loadSupport()` warning](images/launch_positron_runApp.png){width=100%}

:::

-------------------------------------------------

[*What's with the warning?*]{style="font-size: 1.15em; font-weight: bold;"}

In the [Shiny chapter](shiny.qmd) we learned `loadSupport()` is called automatically when an application is run with `runApp()`. Specifically, `loadSupport()` 

> "*loads any top-level supporting .R files in the `R/` directory adjacent to the `app.R`/`server.R`/`ui.R` files*" [^shiny-loadsupport]


[^shiny-loadsupport]: `loadSupport()` does this by sourcing the files in [alphabetical order](https://shiny.posit.co/r/reference/shiny/1.7.3/loadsupport).

Behind the scenes, `runApp()` is called by *both* **Run App/Run Shiny App** buttons, which then automatically calls `loadSupport()`. This is why if we pass our standalone app function to the **Console** (*which uses `shinyApp()`, not `runApp()`*), the warning disappears: 

::: {.panel-tabset}

### RStudio ![](images/rstudio-icon.png){height=20}

![No `loadSupport()` warning in RStudio](images/launch_launch_app_call_rs.png){fig-align='center'}

### Positron ![](images/positron.png){height=20}

![No `loadSupport()` warning in Positron](images/launch_launch_app_call_positron.png){fig-align='center'}

:::

-------------------------------------------------

The examples above demonstrate the differences between calling `shinyApp()` and `runApp()`, and the tension between calling a standalone app function from an R package vs. sourcing the `app.R` file in a Shiny project.

### [`--devmode`]{style="font-weight: bold;"}

As we saw above, clicking **Run Shiny App** in Positron ![](images/positron.png){height=20} will launch the application in [`devmode`](https://shiny.posit.co/r/reference/shiny/latest/devmode.html),[^devmode-exp] which is controlled by the script below:

[^devmode-exp]: [`devmode`](https://shiny.posit.co/r/reference/shiny/latest/devmode.html) is an experimental option with multiple settings. 

```{r}
#| eval: false 
#| code-summary: "show/hide Positron's runShinyApp.R script"
usage <- "Usage: Rscript runShinyApp.R <path> <port> [--devmode]"

args <- commandArgs(trailingOnly = TRUE) # <1>

if (length(args) < 2) {
  stop(usage)
}

path <- args[1]
port <- as.integer(args[2])
stopifnot(is.integer(port))
devmode <- "--devmode" %in% args # <2>

if (devmode) {
  shiny::devmode()
} else {
  options(shiny.autoreload = TRUE)
}

message("Running Shiny app")
message("-----------------")
message(sprintf('shiny::runApp(%s, port = %d)\n', deparse(path), port))

shiny::runApp(path, port = port, launch.browser = FALSE) # <3>
```
1. `commandArgs(trailingOnly = TRUE)` retrieves the arguments passed to the script, excluding the default arguments used when R starts.  
2. `devmode <- "--devmode" %in% args` checks if the `--devmode` flag is present among the arguments. If it is, `devmode` is set to `TRUE`  
3. Lastly, the script runs the Shiny app using `runApp()` (with the specified `path` and `port`), and `launch.browser = FALSE` ensures the app is not automatically opened in a web browser.   

Shiny `devmode` will display *something like* the following messages the first time your application is launched using the **Run Shiny App** button in Positron ![](images/positron.png){height=20}: 

```{bash}
#| eval: false 
#| code-fold: show 
#| code-summary: 'show/hide devmode options'
shiny devmode - Using full shiny javascript file. To use the minified version, call `options(shiny.minified = TRUE)`
This message is displayed once every 8 hours.
shiny devmode - Turning off caching of Sass -> CSS compilation. To turn caching on, call `options(sass.cache = TRUE)`
This message is displayed once every 8 hours.
shiny devmode - Disabling the use of bslib precompiled themes. To be able to use precompiled themes, call `options(bslib.precompiled = TRUE)`
This message is displayed once every 8 hours.
shiny devmode - Enabling warnings about low color contrasts found inside `bslib::bs_theme()`. To suppress these warnings, set `options(bslib.color_contrast_warnings = FALSE)`
This message is displayed once every 8 hours.
```


## Shiny launch functions 

<!-- https://rtask.thinkr.fr/shinyapp-runapp-shinyappdir-difference/ -->

In the following sections, we'll compare `shinyApp()`, `shinyAppDir()`, and `runApp()` to determine which one to use in `R/launch_app.R` and the `app.R` file. As we've seen, the **Run App**/**Run Shiny App** buttons call `runApp()`, even when we have a call to `shinyApp()` in the `app.R` file. This might make you wonder, 

["*Why even include a call to `shinyApp()` if the app is being launched with `runApp()`?*"]{style="font-size: 1.05em; font-weight: bold;"}

Let's review what happens when we call `shinyApp()`.

### [`shinyApp()`]{style="font-size: 0.95em; font-weight: bold;"} {#sec-launch-shiny-app}

One of the key features of `shinyApp()` is the creation of the `shiny.appobj` (a `shiny` app object):

```{r}
#| eval: false 
#| code-fold: false
app <- shinyApp(ui = movies_ui, 
                server = movies_server)
str(app)
```

If we look at the structure of the returned object from `shinyApp()`, we see the `shiny.appobj` includes the `appDir` under `appOptions`: 

``` sh
List of 5
 $ httpHandler     :function (req)  
 $ serverFuncSource:function ()  
 $ onStart         : NULL
 $ options         : list()
 $ appOptions      :List of 2
  ..$ appDir       : chr "/path/to/sap" # <1>
  ..$ bookmarkStore: NULL
 - attr(*, "class")= chr "shiny.appobj" # <2>
```
1. `appDir` is the first argument of `runApp()`   
2. A shiny app object  

This is why `runApp()` works with any `.R` file creating a shiny app object.

:::: {.callout-note collapse="true" appearance="default" title='shinyApp()'}

::: {style='font-size: 1.05em; color: #696969;'}

:::{layout="[45,55]" layout-valign="center"}

[`shinyApp()`]{style="font-size: 0.95em"}: Creates and launches an app defined inline within the call itself (or with UI and server functions passed as arguments).

``` r
shinyApp(
  ui = fluidPage(
    # UI elements
  ),
  server = function(input, output) {
    # Server logic
  }
)
```

:::

:::

::::

### [`shinyAppDir()`]{style="font-size: 0.95em; font-weight: bold;"} {#sec-launch-shiny-app-dir}

`shinyAppDir()` is similar to `shinyApp()`, but is designed to use a "*path to directory that contains a Shiny app.*"

In practice, we can use `shinyAppDir()` with a returned object from `shinyApp()`:

```{r}
#| eval: false 
#| code-fold: false
app <- shinyApp(
        ui = movies_ui,
        server = movies_server
      )
app$appOptions$appDir
```

``` sh
[1] "path/to/sap"
```

This path can be passed to the `appDir` argument (along with any Shiny `options`).

```{r}
#| eval: false 
#| code-fold: false
shinyAppDir(
  appDir = app$appOptions$appDir,
  options(test.mode = TRUE)
)
```

:::: {.callout-note collapse="true" appearance="default" title='shinyAppDir()'}

::: {style='font-size: 1.05em; color: #696969;'}

:::{layout="[45,55]" layout-valign="center"}

[`shinyAppDir()`]{style="font-size: 0.95em"}: Launches an app from a directory (with an `app.R` or `ui.R`/`server.R` files).

``` r
shinyAppDir(
  appDir = "path/to/app/", 
  options = list())
```

:::

:::

::::

### [`runApp()`]{style="font-size: 0.95em; font-weight: bold;"} {#sec-launch-run-app}

The reason we're able to call `runApp()` in the **Console** to launch both applications above is because it's very versatile:

:::{layout="[45,55]" layout-valign="center"}

#### [`runApp()`]{style="font-size: 0.85em"} {.unnumbered}

Can launch apps from `ui.R`/`server.R`, `app.R` or directory:

#### {.unnumbered}

``` r
# In console
runApp()
```

:::

:::{layout="[45,55]" layout-valign="center"}

Works with a path to an `.R` file that creates a `shiny.appobj`:[^launch-run-app-shiny-examples]

[^launch-run-app-shiny-examples]: Shiny's examples are run [using `runApp()`](https://github.com/rstudio/shiny/blob/9ebcbf8a2dec7045f609624d5f339e9a3e29de5f/R/runapp.R#L436)

``` r
runApp(appDir = "path/to/sap")
```

:::

:::{layout="[45,55]" layout-valign="center"}

Can also use a `shiny.appobj` directly:

``` r
app <- shinyApp(
        ui = movies_ui,
        server = movies_server)
runApp(appDir = app)
```

:::

This final method does not produce the `loadSupport()` warning because a Shiny object (`shiny.appobj`) has already been created, and `runApp()` is essentially calling `print(app)` in the **Console**.

:::: {.callout-note collapse="true" appearance="default" title="runApp()"}

::: {style='font-size: 1.05em; color: #696969;'}

:::{layout="[45,55]" layout-valign="center"}

[`runApp()`]{style="font-size: 0.95em"}: A generalized way to launch your app--it can run apps defined inline, or from a directory.

``` r
runApp(
  appDir = "path/to/app/",
  test.mode = TRUE/FALSE)
```

:::

:::

::::

#### Recap {.unnumbered}

1. `shinyApp()` is typically used to create apps within an interactive R session

2. `shinyAppDir()` runs a Shiny app stored in a directory (containing an `app.R` file (or `ui.R` and `server.R` files) 

3. `runApp()` also launches apps in a directory, but it's versatility makes it suitable for running apps in various formats, either defined inline or in separate directories.[^shiny-app-launchers]

[^shiny-app-launchers]: It's worthwhile to read the documentation on  [`shinyApp()`, `shinyAppDir()`](https://shiny.posit.co/r/reference/shiny/0.14/shinyapp), and [`runApp()`](https://shiny.posit.co/r/reference/shiny/1.7.4/runapp).

## Standalone app function 

We'll name our standalone app function `launch_app()` and include the options covered below:

```{r}
#| label: git_box_08_launch-app
#| echo: false
#| results: asis
#| eval: true
git_margin_box(
  contents = "launch",
  fig_pw = '75%', 
  branch = "08_launch-app", 
  repo = 'sap')
```

### [`interactive()`]{style="font-size: 0.90em; font-weight: bold;"} 

The first function option we'll include is a check to see if there is a "*[human operator to interact with](https://stat.ethz.ch/R-manual/R-devel/library/base/help/interactive.html)*" with `base::interactive()`:

```{r}
#| eval: false 
#| code-fold: false
if (interactive()) {
  
} else {
   
}
```

You have probably seen control flow like this in `shiny` help file examples (like `flowLayout()` below):

:::{#fig-launch_if_interactive_examples}

![`if (interactive())` in `flowLayout()` example](images/launch_if_interactive_examples.png){#fig-launch_if_interactive_examples width=100%}

Running examples 'interactively' let's us see the app demo beneath the code
:::

Adding `if` and `interactive()` will allow our standalone app function to distinguish between 1) launching the app from a RStudio/Positron session (i.e., during development) and 2) deploying the application (i.e., like publishing the application on Posit Connect).

### [`options`]{style="font-size: 0.90em; font-weight: bold;"} 

An `options` argument can be passed to `shinyApp()` or `shinyAppDir()`. For example, one of the Shiny options we could include in our standalone app function is `test.mode`:

> '*Should the application be launched in test mode? This is only used for recording or running automated tests. Defaults to the `shiny.testmode` option, or `FALSE` if the option is not set.*'

`test.mode` lets us [export values from our application]((https://shiny.posit.co/r/reference/shiny/1.0.2/exporttestvalues)) when we're running tests (which we'll cover in-depth in the [Tests](@sec-tests) section). 

We'll make `options` an argument (defaulting to an empty `list()`) in our updated  `launch_app()` function.

```{r}
#| eval: false 
#| code-fold: false
launch_app <- function(options = list()) {
    shinyApp(
      ui = movies_ui(), # <1>
      server = movies_server, # <1>
      options = options #  <2>
      )
}
```
1. Build the shiny app object with `movies_ui` and `movies_server`   
2. Include `options` list   


### [`shiny.launch.browser`]{style="font-size: 0.90em; font-weight: bold;"} 

I've written a `display_type()` helper function to 1) check if the application is being run in RStudio and, if so, 2) control where the Shiny app is launched. The `run` argument in `display_type()` takes the following options: 

-   `"p"` = **Viewer Pane**  
-   `"w"` = **IDE Window**   
-   `"b"` = **External browser**   

The option to access configuration is `shiny.launch.browser`:[^launch-shiny.launch.browser]

[^launch-shiny.launch.browser]: The `shiny.launch.browser` options are covered in [this blog post by Garrick Aden-Buie](https://www.garrickadenbuie.com/blog/shiny-tip-option-where-to-run/), and I've combined them into a `run` argument in `launch_app()`

```{r}
#| eval: false 
#| code-fold: false
#' Shiny app display mode helper
#'
#' @param run where to launch app: 
#'  * `"p"` = launch in viewer pane 
#'  * `"b"` = launch in external browser  
#'  * `"w"` = launch in window (default)
#'
#' @return notification of `shinyViewerType` option
#' 
#' @export
#'
display_type <- function(run = "w") {
  if (Sys.getenv("RSTUDIO") == "1") { #<1>
    switch(run, #<2>
      p = options(shiny.launch.browser = .rs.invokeShinyPaneViewer),
      b = options(shiny.launch.browser = .rs.invokeShinyWindowExternal),
      w = options(shiny.launch.browser = .rs.invokeShinyWindowViewer),
      NULL = options(shiny.launch.browser = NULL))#<2>
    environment <- "RStudio"
    shinyViewerType <- getOption('shiny.launch.browser') |> 
                        attributes() |> 
                        unlist() |> 
                        unname()
                      
    cli::cli_alert_info("App running in {environment}")#<3>
    cli::cli_alert_info("shinyViewerType set to {shinyViewerType}")#<4>
  } else {
    environment <- "RStudio"
    cli::cli_alert_info("App not running in {environment}")
  } 
}
```
1. Detect IDE 
2. Set option   
3. Print IDE    
4. Print option   

```{r}
#| label: co_box_cli_dependency
#| echo: false
#| results: asis
#| eval: true
co_box(
  color = "o", 
  look = "default", hsize = "1.10", size = "1.05",
  fold = TRUE,
  header = "New dependency!",
  contents = "
The `cli` package is imported as part the `devtools`/`usethis` workflow but we want to add it the `Imports` field of the `DESCRIPTION` with `usethis::use_package('cli')`.
  "
)
```

### Updates to [`launch_app()`]{style="font-size: 0.90em"} {#sec-launch-standalone-app-function}

The `interactive()` check, `display_type()`, and `test.mode` options have been added to `launch_app()`:

```{r}
#| eval: false 
#| code-fold: false
launch_app <- function(options = list(), run = "w") {
  if (interactive()) { # <1>
    display_type(run = run) # <2>
  }
    shinyApp( # <3>
      ui = movies_ui(),
      server = movies_server,
      options = options
    ) # <3>
}
```
1. Check if interactive (Workbench) launch  
2. Set `shinyViewerType` option with `display_type()`     
3. Launch app     

After loading, documenting, and installing our package, we can see the documentation for our updated `launch_app()` function in RStudio ![](images/rstudio-icon.png){height=20} and Positron ![](images/positron.png){height=20}: 

```{r}
#| label: dev_key_all_00
#| echo: false
#| results: asis
#| eval: true
hot_key("all")
```

:::{#fig-standalone}

:::{layout="[40,60]" layout-valign="top"}

![](images/launch_standalone_rstudio.png){#fig-standalone width='100%'}

![](images/launch_standalone_positron.png){width='100%'}

:::

Standalone app function in Positron and RStudio
:::

In RStudio ![](images/rstudio-icon.png){height=20}, we will confirm the app is launching without the `loadSupport()` warning, the message is printing to the **Console** from the `run` argument, and `test.mode` are implemented correctly.

We also want to confirm `launch_app()` works in Positron ![](images/positron.png){height=20}:

::: {.panel-tabset}

### ![](images/rstudio-icon.png){height=20} `launch_app()`

![`launch_app()` launches the app in the Window](images/launch_launch_app_fun_window.png){width=100%}

### ![](images/rstudio-icon.png){height=20} `launch_app()` args

![The updated `launch_app()` function launches the application in the Viewer](images/launch_launch_app_args.png){width=100%}

### ![](images/positron.png){height=20} `launch_app()`

![The updated `launch_app()` function in Positron](images/launch_launch_app_args_positron.png){width=100%}

:::

When we're confident our standalone app function is working, we'll write the `app.R` file. 

## The [`app.R`]{style="font-size: 0.95em"} file {#sec-launch-app-dot-r}

The `app.R` file should contain any options or settings that we would use during development. There are multiple ways to launch an application from `app.R`, so I encourage you to explore the options below to find a method that works for your workflow/environment.  

### Non-interactive sessions

[What if the session isn't interactive?]{style="font-style: italic; color: #696969; "}

In this case, we'll divert all regular output to the standard error stream.

#### [`stderr()`]{style="font-size: 0.90em; font-weight: bold;"} 

The `sink()` function *"diverts R output to a connection"*, so the code below sends the output that would normally print to the console to the where error messages are written.

```{r}
#| eval: false 
#| code-fold: false
if (!interactive()) {
   sink(stderr(), type = "output")
} else {
   
}
```


This is useful in a non-interactive settings if we want to re-direct the error output for the console text-mode connection.

#### [`tryCatch()`]{style="font-size: 0.90em; font-weight: bold;"} 

`tryCatch()` is used for 'catching conditions' during the execution of an expression (`expr = `):

```{r}
#| eval: false 
#| code-fold: false
if (!interactive()) {
   sink(stderr(), type = "output")
   tryCatch(expr = {
      library(sap)
   }, error = function(e) {
      pkgload::load_all()
   })
} else {
   
}
```

In this case, if `library(sap)` throws an error, the function specified after `error =` is executed (i.e., `pkgload::load_all()`).[^launch-pkgload-load_all]

[^launch-pkgload-load_all]: `pkgload` is part of the [conscious uncoupling](https://www.tidyverse.org/blog/2018/10/devtools-2-0-0/) of the `devtools` package we learned about back in [Chapter 6](dependencies.qmd).

Written this way, in a non-interactive R session, `app.R` will re-direct the error output and attempt to load and attach `sap`, and if this fails, `app.R` will attempt to load all the files in the `R/` folder. 

### Interactive sessions

If the session ***is*** interactive (i.e., `!interactive() == FALSE`), we want `app.R` to load all the code in the `R/` folder with `pkgload::load_all()`.

#### [`pkgload`]{style="font-size: 0.90em; font-weight: bold;"} 

`pkgload::load_all()` is the function that's actually called when we run `devtools::load_all()` (or use [<kbd>Ctrl/Cmd</kbd> + <kbd>Shift</kbd> + <kbd>L</kbd>]{style="font-weight: bold; font-size: 0.75em"}), and this is somewhat analogous to running `library(sap)`

```{r}
#| eval: false 
#| code-fold: false
if (!interactive()) {
   sink(stderr(), type = "output")
   tryCatch(expr = {
      library(sap)
   }, error = function(e) {
      pkgload::load_all()
   })
} else {
   pkgload::load_all()
}
```

```{r}
#| label: co_box_pkgload
#| echo: false
#| results: asis
#| eval: true
co_box(
  color = "o", 
  look = "default", hsize = "1.10", size = "1.05",
  fold = TRUE,
  header = "New dependency!",
  contents = "
The `pkgload` package is imported as part the `devtools`/`usethis` workflow, otherwise we'd want to add it the `Imports` field of the `DESCRIPTION` with `usethis::use_package('pkgload')`.
  "
)
```

#### [`withr`]{style="font-size: 0.90em; font-weight: bold;"} 

The [`withr` package](https://withr.r-lib.org/) is designed to '*run code with safely and temporarily modified global state*', and it comes in handy when launching shiny apps. For example, I want to turn off the `loadSupport()` behavior when launching the app from `app.R`.[^launch-r-folder]

```{r}
#| label: co_box_withr
#| echo: false
#| results: asis
#| eval: true
co_box(
  color = "o", 
  look = "default", hsize = "1.10", size = "1.05",
  fold = TRUE,
  header = "New dependency!",
  contents = "
The `withr` package is imported as part the `devtools`/`usethis` workflow, otherwise we'd want to add it the `Imports` field of the `DESCRIPTION` with `usethis::use_package('withr')`.
  "
)
```


[^launch-r-folder]: You can read more about the `shiny.autoload.r` option and `loadSupport()` in [this article](https://shiny.posit.co/r/articles/build/app-formats/index.html#the-r-directory)

We can use `withr::with_options()` to accomplish this using the following `new` and `code` arguments 

1. `new`: a named list of the *new options and their values*  
2. `code`: the '*Code to execute in the temporary environment*

We'll place the `withr::with_options()` at the top of `app.R` and pass contents of `app.R` into the `code` argument. Just to be sure no options for `shiny.autoload.r` previously exist, we'll also set this option to `NULL` *before* executing the rest of the code.

```{r}
#| eval: false 
#| code-fold: false
withr::with_options(new = list(shiny.autoload.r = FALSE), code = { # <1> 
  if (!interactive()) { # <2> 
    sink(stderr(), type = "output")
    tryCatch(
      expr = {
        library(sap)
      },
      error = function(e) {
        pkgload::load_all()
      }
    ) # <2>
  } else { # <3> 
    pkgload::load_all()
  } # <3> 
    sap::launch_app( # <4>
      options = list(test.mode = TRUE), run = 'p')
})

```
1. Turn off `loadSupport()`  
2. Define non-interactive behaviors  
3. Define interactive behaviors  
4. Launch app (with options)  

Now that we've updated the `app.R` to account for the app-package structure, we'll load, document, and install `sap` and send it's contents to the **Console**: 

```{r}
#| label: dev_key_all_01
#| echo: false
#| results: asis
#| eval: true
hot_key("all")
```



### Updated [`app.R`]{style="font-size: 0.90em"} 

When we send the contents of `app.R` to the **Console**, the `loadSupport()` options are applied before running the app:

::: {.panel-tabset}

### RStudio ![](images/rstudio-icon.png){height=20}

![Sending `app.R` to RStudio's  **Console**](images/launch_app_dot_r.png){width=100%}

### Positron ![](images/positron.png){height=20}

![Sending `app.R` to Positron's **Console**](images/launch_positron_app_dot_r.png){width=100%}

:::

```{r}
#| label: co_box_disable_autoload
#| echo: false
#| results: asis
#| eval: true
co_box(
  color = "g",
  look = "default", hsize = "1.10", size = "1.05",
  fold = TRUE,
  header = "`R/_disable_autoload.R`",
  contents = "
In the documentation for `loadSupport()`, you'll find a second option for removing the `R/` directory sourcing behavior: placing a `_disable_autoload.R` file in the `R/` directory (this is also one of the behaviors of the [`golem` framework](https://github.com/ThinkR-open/golem/blob/365a5cc303b189973abab0dd375c64be79bcf74a/R/disable_autoload.R), which we will cover in the following chapters).
  
Both methods work--this chapter demonstrates a way to remove the `loadSupport()` warning without having to add this file.
  
  "
)
```


## Recap {.unnumbered}

This chapter has covered some options for launching your app within your app-package. We went over what to include in the standalone app function and the `app.R` file, the differences between `shinyApp()`, `shinyAppDir()` and `runApp()`, but it's worth exploring these topics further (especially if you plan on having more than one apps in your package).

```{r}
#| label: co_box_app_recap
#| echo: false
#| results: asis
#| eval: true
co_box(
  color = "g",
  header = "Recap: launching your app",
  look = "default", hsize = "1.10", size = "1.05",
  fold = FALSE,
  contents = "

**`shinyApp()`**: 

-   `shinyApp()` doesn't care about file structure, so it's useful for quick prototyping or if the app is in a single `.R` script. It's also more portable because you can share your app with a single `.R` script.

    -   It's possible to bundle `shinyApp()` in a wrapper function to integrate within an R package (like we've done with `launch_app()`).

    -    `shinyApp()` returns a shiny app object, which can be useful if you want to explore the app structure programmatically (i.e., testing).
  
**`shinyAppDir()`**: 
  
-   `shinyAppDir()` launches an app from a directory, and is useful if an app is spread across multiple files and folders.

**`runApp()`**

-   `runApp()` a more generalized way to launch an app. It works with:
  
    -   apps contained in a directory (i.e., `runApp('path/to/app')`
  
    -   apps in separate `ui.R` and `server.R` files (or a single `app.R` file)
  
    -   a shiny app object (passed to the `appDir` argument).
  
-   Clicking on **Run App** will run the application with `runApp()` if is detects a file (or files) that creates a shiny object.
  
  "
)
```

In the following chapter, we're going to cover where to put non-standard R package files that are common to Shiny apps (`images`, `.css`/`.scss` file, etc.).

```{r}
#| label: git_contrib_box
#| echo: false
#| results: asis
#| eval: true
git_contrib_box()
```