'printing' HTML widgets in programmatically generated Rmarkdown

Question

I'm trying to programmatically generate some Rmarkdown and one of the sections contains an HTML widget. These are output fine if they are last in my function. However, if I wrap them in a print so I can put something else after them as you would do for a plot they do not produce any output.

Perhaps this some something to do with the way knitr handles printing i'm not sure. But does anyone know how I can get HTML widgets to behave like plots do in programmatically generated Rmarkdown?

Example .Rmd

---
title: "R Notebook"
output:
  html_document:
    df_print: paged
---

```{r}
ex_plot <- ggplot2::ggplot(iris, ggplot2::aes(Sepal.Length,Sepal.Width)) + 
    ggplot2::geom_point()

gen_rmarkdown_widget_last <- function() {
    cat("# Head 1\n\n")
    DT::datatable(iris)
}

gen_rmarkdown_plots <- function() {
    cat("# Head 1\n\n")
    print(ex_plot)
    cat("# Head 2\n\n")
}

gen_rmarkdown_widgets <- function() {
    cat("# Head 1\n\n")
    print(DT::datatable(iris))

    # tried loading from file
    # tmp <- tempfile()
    # htmlwidgets::saveWidget(DT::datatable(iris), tmp)
    # knitr::include_url(tmp)
    
    # tried a different widget
    # print(plotly::ggplotly(ex_plot))

    cat("# Head 2\n\n")
}

```

```{r, results='asis'}
# works fine
gen_rmarkdown_widget_last()
```

```{r, results='asis'}
# works fine
gen_rmarkdown_plots()
```

```{r, results='asis'}
# Can't have an HTML widget if it is followed by other things
gen_rmarkdown_widgets()
```

Answer 1

The issue has been discussed here.

Adding the dependencies manually is done with:

data.frame() %>%
  DT::datatable() %>%
  knitr::knit_print() %>%
  attr('knit_meta') %>%
  knitr::knit_meta_add() %>%
  invisible()

In the example you provided:

---
title: "R Notebook"
output:
  html_document:
    df_print: paged
---

```{r}
library(dplyr)
#load dependencies
data.frame() %>%
  DT::datatable() %>%
  knitr::knit_print() %>%
  attr('knit_meta') %>%
  knitr::knit_meta_add() %>%
  invisible()

ex_plot <- ggplot2::ggplot(iris, ggplot2::aes(Sepal.Length,Sepal.Width)) + 
    ggplot2::geom_point()



gen_rmarkdown_widget_last <- function() {
    cat("# Head 1\n\n")
    DT::datatable(iris)
}

gen_rmarkdown_plots <- function() {
    cat("# Head 1\n\n")
    print(ex_plot)
    cat("# Head 2\n\n")
}

gen_rmarkdown_widgets <- function() {
    cat("# Head 1\n\n")
    cat(knitr::knit_print(DT::datatable(iris)))
    cat("\n  \n")
    cat("# Head 2\n\n")
}

```


```{r, results='asis'}
gen_rmarkdown_widgets()
```