react-native/website/versioned_docs/0.49/state.md

---
id: version-0.49-state
title: state
original_id: state
---
<a id="content"></a><h1><a class="anchor" name="state"></a>State <a class="hash-link" href="docs/state.html#state">#</a></h1><div><p>There are two types of data that control a component: <code>props</code> and <code>state</code>. <code>props</code> are set by the parent and they are fixed throughout the lifetime of a component. For data that is going to change, we have to use <code>state</code>.</p><p>In general, you should initialize <code>state</code> in the constructor, and then call <code>setState</code> when you want to change it.</p><p>For example, let's say we want to make text that blinks all the time. The text itself gets set once when the blinking component gets created, so the text itself is a <code>prop</code>. The "whether the text is currently on or off" changes over time, so that should be kept in <code>state</code>.</p><div class="web-player"><div class="prism language-javascript"><span class="token keyword">import</span> React<span class="token punctuation">,</span> <span class="token punctuation">{</span> Component <span class="token punctuation">}</span> <span class="token keyword">from</span> <span class="token string">'react'</span><span class="token punctuation">;</span>
<span class="token keyword">import</span> <span class="token punctuation">{</span> AppRegistry<span class="token punctuation">,</span> Text<span class="token punctuation">,</span> View <span class="token punctuation">}</span> <span class="token keyword">from</span> <span class="token string">'react-native'</span><span class="token punctuation">;</span>

<span class="token keyword">class</span> <span class="token class-name">Blink</span> <span class="token keyword">extends</span> <span class="token class-name">Component</span> <span class="token punctuation">{</span>
  <span class="token function">constructor</span><span class="token punctuation">(</span>props<span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">super</span><span class="token punctuation">(</span>props<span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token keyword">this</span><span class="token punctuation">.</span>state <span class="token operator">=</span> <span class="token punctuation">{</span>showText<span class="token punctuation">:</span> <span class="token boolean">true</span><span class="token punctuation">}</span><span class="token punctuation">;</span>

   <span class="token comment" spellcheck="true"> // Toggle the state every second
</span>    <span class="token function">setInterval</span><span class="token punctuation">(</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">=&gt;</span> <span class="token punctuation">{</span>
      <span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">setState</span><span class="token punctuation">(</span>previousState <span class="token operator">=&gt;</span> <span class="token punctuation">{</span>
        <span class="token keyword">return</span> <span class="token punctuation">{</span> showText<span class="token punctuation">:</span> <span class="token operator">!</span>previousState<span class="token punctuation">.</span>showText <span class="token punctuation">}</span><span class="token punctuation">;</span>
      <span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span><span class="token punctuation">,</span> <span class="token number">1000</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
  <span class="token punctuation">}</span>

  <span class="token function">render</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">let</span> display <span class="token operator">=</span> <span class="token keyword">this</span><span class="token punctuation">.</span>state<span class="token punctuation">.</span>showText <span class="token operator">?</span> <span class="token keyword">this</span><span class="token punctuation">.</span>props<span class="token punctuation">.</span>text <span class="token punctuation">:</span> <span class="token string">' '</span><span class="token punctuation">;</span>
    <span class="token keyword">return</span> <span class="token punctuation">(</span>
      <span class="token operator">&lt;</span>Text<span class="token operator">&gt;</span><span class="token punctuation">{</span>display<span class="token punctuation">}</span><span class="token operator">&lt;</span><span class="token operator">/</span>Text<span class="token operator">&gt;</span>
    <span class="token punctuation">)</span><span class="token punctuation">;</span>
  <span class="token punctuation">}</span>
<span class="token punctuation">}</span>

<span class="token keyword">export</span> <span class="token keyword">default</span> <span class="token keyword">class</span> <span class="token class-name">BlinkApp</span> <span class="token keyword">extends</span> <span class="token class-name">Component</span> <span class="token punctuation">{</span>
  <span class="token function">render</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">return</span> <span class="token punctuation">(</span>
      <span class="token operator">&lt;</span>View<span class="token operator">&gt;</span>
        <span class="token operator">&lt;</span>Blink text<span class="token operator">=</span><span class="token string">'I love to blink'</span> <span class="token operator">/</span><span class="token operator">&gt;</span>
        <span class="token operator">&lt;</span>Blink text<span class="token operator">=</span><span class="token string">'Yes blinking is so great'</span> <span class="token operator">/</span><span class="token operator">&gt;</span>
        <span class="token operator">&lt;</span>Blink text<span class="token operator">=</span><span class="token string">'Why did they ever take this out of HTML'</span> <span class="token operator">/</span><span class="token operator">&gt;</span>
        <span class="token operator">&lt;</span>Blink text<span class="token operator">=</span><span class="token string">'Look at me look at me look at me'</span> <span class="token operator">/</span><span class="token operator">&gt;</span>
      <span class="token operator">&lt;</span><span class="token operator">/</span>View<span class="token operator">&gt;</span>
    <span class="token punctuation">)</span><span class="token punctuation">;</span>
  <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
<span class="token comment" spellcheck="true">
// skip this line if using Create React Native App
</span>AppRegistry<span class="token punctuation">.</span><span class="token function">registerComponent</span><span class="token punctuation">(</span><span class="token string">'AwesomeProject'</span><span class="token punctuation">,</span> <span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">=&gt;</span> BlinkApp<span class="token punctuation">)</span><span class="token punctuation">;</span></div><iframe style="margin-top:4px;" width="880" height="420" data-src="//cdn.rawgit.com/dabbott/react-native-web-player/gh-v1.2.6/index.html#code=import%20React%2C%20%7B%20Component%20%7D%20from%20'react'%3B%0Aimport%20%7B%20AppRegistry%2C%20Text%2C%20View%20%7D%20from%20'react-native'%3B%0A%0Aclass%20Blink%20extends%20Component%20%7B%0A%20%20constructor(props)%20%7B%0A%20%20%20%20super(props)%3B%0A%20%20%20%20this.state%20%3D%20%7BshowText%3A%20true%7D%3B%0A%0A%20%20%20%20%2F%2F%20Toggle%20the%20state%20every%20second%0A%20%20%20%20setInterval(()%20%3D%3E%20%7B%0A%20%20%20%20%20%20this.setState(previousState%20%3D%3E%20%7B%0A%20%20%20%20%20%20%20%20return%20%7B%20showText%3A%20!previousState.showText%20%7D%3B%0A%20%20%20%20%20%20%7D)%3B%0A%20%20%20%20%7D%2C%201000)%3B%0A%20%20%7D%0A%0A%20%20render()%20%7B%0A%20%20%20%20let%20display%20%3D%20this.state.showText%20%3F%20this.props.text%20%3A%20'%20'%3B%0A%20%20%20%20return%20(%0A%20%20%20%20%20%20%3CText%3E%7Bdisplay%7D%3C%2FText%3E%0A%20%20%20%20)%3B%0A%20%20%7D%0A%7D%0A%0Aexport%20default%20class%20BlinkApp%20extends%20Component%20%7B%0A%20%20render()%20%7B%0A%20%20%20%20return%20(%0A%20%20%20%20%20%20%3CView%3E%0A%20%20%20%20%20%20%20%20%3CBlink%20text%3D'I%20love%20to%20blink'%20%2F%3E%0A%20%20%20%20%20%20%20%20%3CBlink%20text%3D'Yes%20blinking%20is%20so%20great'%20%2F%3E%0A%20%20%20%20%20%20%20%20%3CBlink%20text%3D'Why%20did%20they%20ever%20take%20this%20out%20of%20HTML'%20%2F%3E%0A%20%20%20%20%20%20%20%20%3CBlink%20text%3D'Look%20at%20me%20look%20at%20me%20look%20at%20me'%20%2F%3E%0A%20%20%20%20%20%20%3C%2FView%3E%0A%20%20%20%20)%3B%0A%20%20%7D%0A%7D%0A%0A%2F%2F%20skip%20this%20line%20if%20using%20Create%20React%20Native%20App%0AAppRegistry.registerComponent('AwesomeProject'%2C%20()%20%3D%3E%20BlinkApp)%3B" frameborder="0"></iframe></div><p>In a real application, you probably won't be setting state with a timer. You might set state when you have new data arrive from the server, or from user input. You can also use a state container like <a href="http://redux.js.org/index.html" target="_blank">Redux</a> to control your data flow. In that case you would use Redux to modify your state rather than calling <code>setState</code> directly.</p><p>When setState is called, BlinkApp will re-render its Component. By calling setState within the Timer, the component will re-render every time the Timer ticks.</p><p>State works the same way as it does in React, so for more details on handling state, you can look at the <a href="https://facebook.github.io/react/docs/component-api.html" target="_blank">React.Component API</a>.
At this point, you might be annoyed that most of our examples so far use boring default black text. To make things more beautiful, you will have to <a href="docs/style.html" target="_blank">learn about Style</a>.</p></div><div class="docs-prevnext"><a class="docs-prev btn" href="docs/props.html#content">← Previous</a><a class="docs-next btn" href="docs/style.html#content">Continue Reading →</a></div><p class="edit-page-block"><a target="_blank" href="https://github.com/facebook/react-native/blob/master/docs/State.md">Improve this page</a> by sending a pull request!</p>