github/shiny
1
1
Fork 0
mirror of https://github.com/rstudio/shiny.git synced 2026-01-10 23:48:01 -05:00
Code Issues Packages Projects Releases Wiki Activity
Files
cf665e5c19920b77eb02fc25ae292f2c2f33f1e1
shiny/reference/reactiveVal.html
schloerke cf665e5c19 Built site for shiny@1.12.0: 8183dfd
2025-11-13 20:59:50 +00:00

172 lines
14 KiB
HTML
Raw Blame History

<!DOCTYPE html>
<!-- Generated by pkgdown: do not edit by hand --><html lang="en"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><meta charset="utf-8"><meta http-equiv="X-UA-Compatible" content="IE=edge"><meta name="viewport" content="width=device-width, initial-scale=1.0"><title>Create a (single) reactive value — reactiveVal • shiny</title><!-- jquery --><script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.7.1/jquery.min.js" integrity="sha512-v2CJ7UaYy4JwqLDIrZUI/4hqeoQieOmAZNXBeQyjo21dadnwR+8ZaIJVT8EE2iyI61OV8e6M8PP2/4hpQINQ/g==" crossorigin="anonymous" referrerpolicy="no-referrer"></script><!-- Bootstrap --><link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/3.4.1/css/bootstrap.min.css" integrity="sha256-bZLfwXAP04zRMK2BjiO8iu9pf4FbLqX6zitd+tIvLhE=" crossorigin="anonymous"><script src="https://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/3.4.1/js/bootstrap.min.js" integrity="sha256-nuL8/2cJ5NDSSwnKD8VqreErSWHtnEP9E7AySL+1ev4=" crossorigin="anonymous"></script><!-- bootstrap-toc --><link rel="stylesheet" href="../bootstrap-toc.css"><script src="../bootstrap-toc.js"></script><!-- Font Awesome icons --><link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/5.12.1/css/all.min.css" integrity="sha256-mmgLkCYLUQbXn0B1SRqzHar6dCnv9oZFPEC1g1cwlkk=" crossorigin="anonymous"><link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/5.12.1/css/v4-shims.min.css" integrity="sha256-wZjR52fzng1pJHwx4aV2AO3yyTOXrcDW7jBpJtTwVxw=" crossorigin="anonymous"><!-- clipboard.js --><script src="https://cdnjs.cloudflare.com/ajax/libs/clipboard.js/2.0.6/clipboard.min.js" integrity="sha256-inc5kl9MA1hkeYUt+EC3BhlIgyp/2jDIyBLS6k3UxPI=" crossorigin="anonymous"></script><!-- headroom.js --><script src="https://cdnjs.cloudflare.com/ajax/libs/headroom/0.11.0/headroom.min.js" integrity="sha256-AsUX4SJE1+yuDu5+mAVzJbuYNPHj/WroHuZ8Ir/CkE0=" crossorigin="anonymous"></script><script src="https://cdnjs.cloudflare.com/ajax/libs/headroom/0.11.0/jQuery.headroom.min.js" integrity="sha256-ZX/yNShbjqsohH1k95liqY9Gd8uOiE1S4vZc+9KQ1K4=" crossorigin="anonymous"></script><!-- pkgdown --><link href="../pkgdown.css" rel="stylesheet"><script src="../pkgdown.js"></script><meta property="og:title" content="Create a (single) reactive value — reactiveVal"><meta property="og:description" content='The reactiveVal function is used to construct a "reactive value"
object. This is an object used for reading and writing a value, like a
variable, but with special capabilities for reactive programming. When you
read the value out of a reactiveVal object, the calling reactive expression
takes a dependency, and when you change the value, it notifies any reactives
that previously depended on that value.'><meta property="og:image" content="/logo.png"><!-- mathjax --><script src="https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.5/MathJax.js" integrity="sha256-nvJJv9wWKEm88qvoQl9ekL2J+k/RWIsaSScxxlsrv8k=" crossorigin="anonymous"></script><script src="https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.5/config/TeX-AMS-MML_HTMLorMML.js" integrity="sha256-84DKXVJXs0/F8OTMzX4UR909+jtl4G7SPypPavF+GfA=" crossorigin="anonymous"></script><!--[if lt IE 9]>
<script src="https://oss.maxcdn.com/html5shiv/3.7.3/html5shiv.min.js"></script>
<script src="https://oss.maxcdn.com/respond/1.4.2/respond.min.js"></script>
<![endif]--></head><body data-spy="scroll" data-target="#toc">
<div class="container template-reference-topic">
<header><div class="navbar navbar-default navbar-fixed-top" role="navigation">
<div class="container">
<div class="navbar-header">
<button type="button" class="navbar-toggle collapsed" data-toggle="collapse" data-target="#navbar" aria-expanded="false">
<span class="sr-only">Toggle navigation</span>
<span class="icon-bar"></span>
<span class="icon-bar"></span>
<span class="icon-bar"></span>
</button>
<span class="navbar-brand">
<a class="navbar-link" href="../index.html">shiny</a>
<span class="version label label-default" data-toggle="tooltip" data-placement="bottom" title="">1.12.0</span>
</span>
</div>
<div id="navbar" class="navbar-collapse collapse">
<ul class="nav navbar-nav"><li>
<a href="../reference/index.html">Reference</a>
</li>
<li>
<a href="../news/index.html">Changelog</a>
</li>
</ul><ul class="nav navbar-nav navbar-right"><li>
<a href="https://github.com/rstudio/shiny/" class="external-link">
<span class="fab fa-github fa-lg"></span>
</a>
</li>
</ul></div><!--/.nav-collapse -->
</div><!--/.container -->
</div><!--/.navbar -->
</header><div class="row">
<div class="col-md-9 contents">
<div class="page-header">
<h1>Create a (single) reactive value</h1>
<small class="dont-index">Source: <a href="https://github.com/rstudio/shiny/blob/rc-v1.12.0/R/reactives.R" class="external-link"><code>R/reactives.R</code></a></small>
<div class="hidden name"><code>reactiveVal.Rd</code></div>
</div>
<div class="ref-description">
<p>The <code>reactiveVal</code> function is used to construct a "reactive value"
object. This is an object used for reading and writing a value, like a
variable, but with special capabilities for reactive programming. When you
read the value out of a reactiveVal object, the calling reactive expression
takes a dependency, and when you change the value, it notifies any reactives
that previously depended on that value.</p>
</div>
<div id="ref-usage">
<div class="sourceCode"><pre class="sourceCode r"><code><span><span class="fu">reactiveVal</span><span class="op">(</span>value <span class="op">=</span> <span class="cn">NULL</span>, label <span class="op">=</span> <span class="cn">NULL</span><span class="op">)</span></span></code></pre></div>
</div>
<div id="arguments">
<h2>Arguments</h2>
<dl><dt id="arg-value">value<a class="anchor" aria-label="anchor" href="#arg-value"></a></dt>
<dd><p>An optional initial value.</p></dd>
<dt id="arg-label">label<a class="anchor" aria-label="anchor" href="#arg-label"></a></dt>
<dd><p>An optional label, for debugging purposes (see
<code><a href="reactlog.html">reactlog()</a></code>). If missing, a label will be automatically
created.</p></dd>
</dl></div>
<div id="value">
<h2>Value</h2>
<p>A function. Call the function with no arguments to (reactively) read
the value; call the function with a single argument to set the value.</p>
</div>
<div id="details">
<h2>Details</h2>
<p><code>reactiveVal</code> is very similar to <code><a href="reactiveValues.html">reactiveValues()</a></code>, except
that the former is for a single reactive value (like a variable), whereas the
latter lets you conveniently use multiple reactive values by name (like a
named list of variables). For a one-off reactive value, it's more natural to
use <code>reactiveVal</code>. See the Examples section for an illustration.</p>
</div>
<div id="ref-examples">
<h2>Examples</h2>
<div class="sourceCode"><pre class="sourceCode r"><code><span class="r-in"><span></span></span>
<span class="r-in"><span><span class="kw">if</span> <span class="op">(</span><span class="cn">FALSE</span><span class="op">)</span> <span class="op">{</span> <span class="co"># \dontrun{</span></span></span>
<span class="r-in"><span></span></span>
<span class="r-in"><span><span class="co"># Create the object by calling reactiveVal</span></span></span>
<span class="r-in"><span><span class="va">r</span> <span class="op">&lt;-</span> <span class="fu">reactiveVal</span><span class="op">(</span><span class="op">)</span></span></span>
<span class="r-in"><span></span></span>
<span class="r-in"><span><span class="co"># Set the value by calling with an argument</span></span></span>
<span class="r-in"><span><span class="fu">r</span><span class="op">(</span><span class="fl">10</span><span class="op">)</span></span></span>
<span class="r-in"><span></span></span>
<span class="r-in"><span><span class="co"># Read the value by calling without arguments</span></span></span>
<span class="r-in"><span><span class="fu">r</span><span class="op">(</span><span class="op">)</span></span></span>
<span class="r-in"><span></span></span>
<span class="r-in"><span><span class="op">}</span> <span class="co"># }</span></span></span>
<span class="r-in"><span></span></span>
<span class="r-in"><span><span class="co">## Only run examples in interactive R sessions</span></span></span>
<span class="r-in"><span><span class="kw">if</span> <span class="op">(</span><span class="fu"><a href="https://rdrr.io/r/base/interactive.html" class="external-link">interactive</a></span><span class="op">(</span><span class="op">)</span><span class="op">)</span> <span class="op">{</span></span></span>
<span class="r-in"><span></span></span>
<span class="r-in"><span><span class="va">ui</span> <span class="op">&lt;-</span> <span class="fu"><a href="fluidPage.html">fluidPage</a></span><span class="op">(</span></span></span>
<span class="r-in"><span> <span class="fu"><a href="actionButton.html">actionButton</a></span><span class="op">(</span><span class="st">"minus"</span>, <span class="st">"-1"</span><span class="op">)</span>,</span></span>
<span class="r-in"><span> <span class="fu"><a href="actionButton.html">actionButton</a></span><span class="op">(</span><span class="st">"plus"</span>, <span class="st">"+1"</span><span class="op">)</span>,</span></span>
<span class="r-in"><span> <span class="fu"><a href="https://rstudio.github.io/htmltools/reference/builder.html" class="external-link">br</a></span><span class="op">(</span><span class="op">)</span>,</span></span>
<span class="r-in"><span> <span class="fu"><a href="textOutput.html">textOutput</a></span><span class="op">(</span><span class="st">"value"</span><span class="op">)</span></span></span>
<span class="r-in"><span><span class="op">)</span></span></span>
<span class="r-in"><span></span></span>
<span class="r-in"><span><span class="co"># The comments below show the equivalent logic using reactiveValues()</span></span></span>
<span class="r-in"><span><span class="va">server</span> <span class="op">&lt;-</span> <span class="kw">function</span><span class="op">(</span><span class="va">input</span>, <span class="va">output</span>, <span class="va">session</span><span class="op">)</span> <span class="op">{</span></span></span>
<span class="r-in"><span> <span class="va">value</span> <span class="op">&lt;-</span> <span class="fu">reactiveVal</span><span class="op">(</span><span class="fl">0</span><span class="op">)</span> <span class="co"># rv &lt;- reactiveValues(value = 0)</span></span></span>
<span class="r-in"><span></span></span>
<span class="r-in"><span> <span class="fu"><a href="observeEvent.html">observeEvent</a></span><span class="op">(</span><span class="va">input</span><span class="op">$</span><span class="va">minus</span>, <span class="op">{</span></span></span>
<span class="r-in"><span> <span class="va">newValue</span> <span class="op">&lt;-</span> <span class="fu">value</span><span class="op">(</span><span class="op">)</span> <span class="op">-</span> <span class="fl">1</span> <span class="co"># newValue &lt;- rv$value - 1</span></span></span>
<span class="r-in"><span> <span class="fu">value</span><span class="op">(</span><span class="va">newValue</span><span class="op">)</span> <span class="co"># rv$value &lt;- newValue</span></span></span>
<span class="r-in"><span> <span class="op">}</span><span class="op">)</span></span></span>
<span class="r-in"><span></span></span>
<span class="r-in"><span> <span class="fu"><a href="observeEvent.html">observeEvent</a></span><span class="op">(</span><span class="va">input</span><span class="op">$</span><span class="va">plus</span>, <span class="op">{</span></span></span>
<span class="r-in"><span> <span class="va">newValue</span> <span class="op">&lt;-</span> <span class="fu">value</span><span class="op">(</span><span class="op">)</span> <span class="op">+</span> <span class="fl">1</span> <span class="co"># newValue &lt;- rv$value + 1</span></span></span>
<span class="r-in"><span> <span class="fu">value</span><span class="op">(</span><span class="va">newValue</span><span class="op">)</span> <span class="co"># rv$value &lt;- newValue</span></span></span>
<span class="r-in"><span> <span class="op">}</span><span class="op">)</span></span></span>
<span class="r-in"><span></span></span>
<span class="r-in"><span> <span class="va">output</span><span class="op">$</span><span class="va">value</span> <span class="op">&lt;-</span> <span class="fu"><a href="renderPrint.html">renderText</a></span><span class="op">(</span><span class="op">{</span></span></span>
<span class="r-in"><span> <span class="fu">value</span><span class="op">(</span><span class="op">)</span> <span class="co"># rv$value</span></span></span>
<span class="r-in"><span> <span class="op">}</span><span class="op">)</span></span></span>
<span class="r-in"><span><span class="op">}</span></span></span>
<span class="r-in"><span></span></span>
<span class="r-in"><span><span class="fu"><a href="shinyApp.html">shinyApp</a></span><span class="op">(</span><span class="va">ui</span>, <span class="va">server</span><span class="op">)</span></span></span>
<span class="r-in"><span></span></span>
<span class="r-in"><span><span class="op">}</span></span></span>
<span class="r-in"><span></span></span>
</code></pre></div>
</div>
</div>
<div class="col-md-3 hidden-xs hidden-sm" id="pkgdown-sidebar">
<nav id="toc" data-toggle="toc" class="sticky-top"><h2 data-toc-skip>Contents</h2>
</nav></div>
</div>
<footer><div class="copyright">
<p></p><p>Developed by Winston Chang, Joe Cheng, JJ Allaire, Carson Sievert, Barret Schloerke, Garrick Aden-Buie, Yihui Xie, Jeff Allen, Jonathan McPherson, Alan Dipert, Barbara Borges, Posit Software, PBC.</p>
</div>
<div class="pkgdown">
<p></p><p>Site built with <a href="https://pkgdown.r-lib.org/" class="external-link">pkgdown</a> 2.2.0.</p>
</div>
</footer></div>
</body></html>
Reference in New Issue View Git Blame Copy Permalink