title: Flutter invalid refrence to 'this' expression
body: <p>i am trying to add item in list when i click on add button, all code is ok, but i am getting error invalid reference to <code>this</code> expression. i am using <code>stateful</code> widget.</p>
  
  <pre><code>List&lt;Widget&gt; _listSection = [];
              body: Container(
                child: Stack(
                  children: [
  
                    FloatingActionButton(
                      onPressed: () {
                        _listSection.add(
                          listSectionMethod(
                              "title three", "hello from click", Icons.forward),
                        );
  
                        setState(() {});
                      },
                    ),
                  ],
                ),
              ),
            ),
          );
        }
      }
  
      Widget listSection = Container(
        margin: EdgeInsets.only(top: 210),
        child: ListView(
          children: [
            Column(
              children: [
                Column(
                  children: this._listSection, // ----&gt; ERROR HERE
                ),
              ],
            ),
          ],
        ),
      );
  </code></pre>
  
  <p><strong>List Section Method:</strong></p>
  
  <pre><code>Card listSectionMethod(String title, String subtitle, IconData icon) {
    return new Card(
      child: ListTile(
        title: Text(
          title,
          style: TextStyle(fontWeight: FontWeight.bold),
        ),
        subtitle: Text(subtitle),
        trailing: Icon(
          icon,
          color: Colors.blue,
        ),
      ),
    );
  }
  </code></pre>