title: Changing property of children don't trigger UI change on Flutter Getx
body: <p>I'm trying to render a reactive widget, based on a object list.</p>
  <p>I needed that when the children of this object, has his boolean property changes, the UI should be updated.</p>
  <p>In this scenario, my controller has a list os Sections and each section has a list of Lessons.</p>
  <p>To better understanding, i rewriter my code making a simple example, based on what i need.
  I already try using .map, .forEach, and others approaches, but the children property never trigger the UI update.</p>
  <pre><code>GetX&lt;LessonController&gt;(
    initState: (state) =&gt; controller.getLessonsByCourse(course.id),
    builder: (_) {
      return Expanded(
        child: ListView.separated(
          scrollDirection: Axis.vertical,
          itemCount: _.sectionList.length,
          itemBuilder: (BuildContext context, int index) {
            return ExpansionTile(
                title: Text(_.sectionList[index].title),
                children: &lt;Widget&gt;[
                  for(var i = 0; i &lt; _.sectionList[index].lessons.length; i++)
                    Padding(
                      padding: const EdgeInsets.all(8.0),
                      child: 
                        Obx(() =&gt; 
                          GestureDetector(
                            child: Text((_.sectionList[index].lessons[i] as Lesson).isCompleted.toString()),
                            onTap: () {
                              (_.sectionList[index].lessons[i] as Lesson).isCompleted = !(_.sectionList[index].lessons[i]as Lesson).isCompleted;
                              print((_.sectionList[index].lessons[i]as Lesson).isCompleted.toString());
                            })
                        ),
                    )
                ]);
          },
          separatorBuilder: (context, ind) =&gt; Divider(
            height: 2,
            color: Colors.grey[300],
          ),
        ),
      );
    })
  </code></pre>
  <p><strong>Solution:</strong></p>
  <p>The GetX container monitores changes on the list items, so when you change a property from one of this items, the list itself doesn't change. To solved that, i change the item property, and after that i overrited it on the list.</p>
  <pre><code>onTap: (value) {
      Section tappedSection = _.sectionList[index];
      tappedSection.lessons[lessonIndex].isCompleted = value;
      // This is the secret
      // Making GetX detect a change on the list and rebuild UI
      _.sectionList[index] = tappedSection;
  }));
  </code></pre>