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    <h5>SideBarContentState class</h5>
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      <li class="section-title"><a href="pages_SideBarContent/SideBarContentState-class.html#constructors">Constructors</a></li>
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    <h1>setState method</h1>

    <section class="multi-line-signature">
      <div>
        <ol class="annotation-list">
          <li>@protected</li>
        </ol>
      </div>
      <span class="returntype">void</span>
      <span class="name ">setState</span>
(<wbr><span class="parameter" id="setState-param-fn"><span class="type-annotation">VoidCallback</span> <span class="parameter-name">fn</span></span>)
      <div class="features">@protected, inherited</div>
    </section>
    <section class="desc markdown">
      <p>Notify the framework that the internal state of this object has changed.</p>
<p>Whenever you change the internal state of a <code>State</code> object, make the
change in a function that you pass to <a href="pages_SideBarContent/SideBarContentState/setState.html">setState</a>:</p>
<pre class="language-dart"><code class="language-dart">setState(() { _myState = newValue });
</code></pre>
<p>The provided callback is immediately called synchronously. It must not
return a future (the callback cannot be <code>async</code>), since then it would be
unclear when the state was actually being set.</p>
<p>Calling <a href="pages_SideBarContent/SideBarContentState/setState.html">setState</a> notifies the framework that the internal state of this
object has changed in a way that might impact the user interface in this
subtree, which causes the framework to schedule a <a href="pages_SideBarContent/SideBarContentState/build.html">build</a> for this <code>State</code>
object.</p>
<p>If you just change the state directly without calling <a href="pages_SideBarContent/SideBarContentState/setState.html">setState</a>, the
framework might not schedule a <a href="pages_SideBarContent/SideBarContentState/build.html">build</a> and the user interface for this
subtree might not be updated to reflect the new state.</p>
<p>Generally it is recommended that the <code>setState</code> method only be used to
wrap the actual changes to the state, not any computation that might be
associated with the change. For example, here a value used by the <a href="pages_SideBarContent/SideBarContentState/build.html">build</a>
function is incremented, and then the change is written to disk, but only
the increment is wrapped in the <code>setState</code>:</p>
<pre class="language-dart"><code class="language-dart">Future&lt;void&gt; _incrementCounter() async {
  setState(() {
    _counter++;
  });
  Directory directory = await getApplicationDocumentsDirectory();
  final String dirName = directory.path;
  await File('$dir/counter.txt').writeAsString('$_counter');
}
</code></pre>
<p>It is an error to call this method after the framework calls <a href="pages_SideBarContent/SideBarContentState/dispose.html">dispose</a>.
You can determine whether it is legal to call this method by checking
whether the <a href="pages_SideBarContent/SideBarContentState/mounted.html">mounted</a> property is true.</p>
    </section>
    
    <section class="summary source-code" id="source">
      <h2><span>Implementation</span> </h2>
      <pre class="language-dart"><code class="language-dart">@protected
void setState(VoidCallback fn) {
  assert(fn != null);
  assert(() {
    if (_debugLifecycleState == _StateLifecycle.defunct) {
      throw FlutterError(
        &#39;setState() called after dispose(): $this\n&#39;
        &#39;This error happens if you call setState() on a State object for a widget that &#39;
        &#39;no longer appears in the widget tree (e.g., whose parent widget no longer &#39;
        &#39;includes the widget in its build). This error can occur when code calls &#39;
        &#39;setState() from a timer or an animation callback. The preferred solution is &#39;
        &#39;to cancel the timer or stop listening to the animation in the dispose() &#39;
        &#39;callback. Another solution is to check the &quot;mounted&quot; property of this &#39;
        &#39;object before calling setState() to ensure the object is still in the &#39;
        &#39;tree.\n&#39;
        &#39;This error might indicate a memory leak if setState() is being called &#39;
        &#39;because another object is retaining a reference to this State object &#39;
        &#39;after it has been removed from the tree. To avoid memory leaks, &#39;
        &#39;consider breaking the reference to this object during dispose().&#39;
      );
    }
    if (_debugLifecycleState == _StateLifecycle.created &amp;&amp; !mounted) {
      throw FlutterError(
        &#39;setState() called in constructor: $this\n&#39;
        &#39;This happens when you call setState() on a State object for a widget that &#39;
        &#39;hasn\&#39;t been inserted into the widget tree yet. It is not necessary to call &#39;
        &#39;setState() in the constructor, since the state is already assumed to be dirty &#39;
        &#39;when it is initially created.&#39;
      );
    }
    return true;
  }());
  final dynamic result = fn() as dynamic;
  assert(() {
    if (result is Future) {
      throw FlutterError(
        &#39;setState() callback argument returned a Future.\n&#39;
        &#39;The setState() method on $this was called with a closure or method that &#39;
        &#39;returned a Future. Maybe it is marked as &quot;async&quot;.\n&#39;
        &#39;Instead of performing asynchronous work inside a call to setState(), first &#39;
        &#39;execute the work (without updating the widget state), and then synchronously &#39;
        &#39;update the state inside a call to setState().&#39;
      );
    }
    &#47;&#47; We ignore other types of return values so that you can do things like:
    &#47;&#47;   setState(() =&gt; x = 3);
    return true;
  }());
  _element.markNeedsBuild();
}</code></pre>
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