title: Detect focused widget in flutter listview
body: <p>I have an horizontal listview.builder widget, each child in the list is about 90℅ of the total width, how can I detect which widget is in focus. </p>
  
  <p>This is my the widget.</p>
  
  <pre><code>new ListView.builder(
                                scrollDirection: Axis.horizontal,
                                itemCount: categories.length,
                                itemBuilder: (context, index) {
                                  return new InkWell(
                                    onTap: () {
                                      Navigator
                                          .of(context)
                                          .push(new MaterialPageRoute(
                                            builder: (_) =&gt; new StakePage(),
                                          ));
                                    },
                                    child: new Card(
                                      child: new Container(
                                        decoration: new BoxDecoration(
                                          image: new DecorationImage(
                                            fit: BoxFit.cover,
                                            image: categories[index].cover,
                                            colorFilter: new ColorFilter.mode(
                                                Colors.black12,
                                                BlendMode.screen),
                                          ),
                                        ),
                                        constraints: new BoxConstraints(
                                            maxWidth: 400.0,
                                            maxHeight: 600.0),
                                        height: size.height / 2,
                                        width: size.width * 0.85,
                                      ),
                                    ),
                                  );
                                }),
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/6aOy3.png" rel="noreferrer"><img src="https://i.stack.imgur.com/6aOy3.png" alt="It looks like this"></a></p>