title: Expansion Panel List in Flutter
body: <p>I am new to flutter and I am stuck on a problem. I am trying to make a expansion panel list. I am able to make the list but not able to make the expansion panels expand or collapse.I am attaching the code. Please have a look at it and let me know the problem.</p>
  
  <pre><code>ExpansionPanelList criteria;
  criteria = new ExpansionPanelList(
    children: &lt;ExpansionPanel&gt;[
      new ExpansionPanel(
        headerBuilder: schoolheaderBuilder,
        body: new Text("school"),
        isExpanded: false,
      ),
      new ExpansionPanel(
        headerBuilder: hospitalheaderBuilder,
        body: new Text("hospital"),
      ),
      new ExpansionPanel(
          headerBuilder: vaheaderBuilder,
          body: new Text("va facility"),
          isExpanded: false),
      new ExpansionPanel(
          headerBuilder: restheaderBuilder,
          body: new Text("Restaurants"),
          isExpanded: false),
      new ExpansionPanel(
          headerBuilder: crimeheaderBuilder,
          body: new Text("Crime"),
          isExpanded: false),
      new ExpansionPanel(
          headerBuilder: commuteheaderBuilder,
          body: new Text("Commute"),
          isExpanded: false),
      new ExpansionPanel(
          headerBuilder: incomeBuilder,
          body: new Text("Household Income"),
          isExpanded: false),
      new ExpansionPanel(
          headerBuilder: househeaderBuilder,
          body: new Text("House Value"),
          isExpanded: false)
    ],
    expansionCallback: (int index, bool isExpanded)
    {
      isExpanded = !criteria.children[index].isExpanded;
    },
  );
  </code></pre>