title: Flutter - How to enable AnimatedOpacity automatically?
body: <p>I'm creating a dashboard which contain Tween animation for two widgets, Text and two Container. But, I want to make the two Container's opacity changing slowly from invisible to visible...so I used AnimatedOpacity. But I don't know how to do it...</p>
  
  <p><strong><em>Any help would be appreciated..</em></strong></p>
  
  <pre><code>class _IntroState extends State&lt;Intro&gt; with SingleTickerProviderStateMixin {
    Animation animation;
    AnimationController animationController;
  
     @override
     void initState() {
       super.initState();
        animationController = AnimationController(
          duration: Duration(seconds: 2),
          vsync: this,
       );
  
      animation = Tween(begin: -1.0, end: 0.0).animate(CurvedAnimation(
          parent: animationController, curve: Curves.fastOutSlowIn));
      animationController.forward();
    }
  
    @override
    Widget build(BuildContext context) {
      bool _visible = false;
      final double width = MediaQuery.of(context).size.width;
  
    return AnimatedBuilder(
        animation: animationController,
        builder: (BuildContext context, Widget child) {
           return Scaffold(
             //BODDY
              body: ListView(
                hildren:&lt;Widget&gt;[
                   new Stack(
                     children: &lt;Widget&gt;[
                       new Transform(
                         //ANIMATED OPACITY
                         new AnimatedOpacity(
                            opacity: _visible ? 0.0 : 1.0,
                            duration: Duration(milliseconds: 500),
                            child: new Padding(
                              padding: const EdgeInsets.symmetric(
                                    horizontal: 12.0),
                              child: new Row(
                                 children: &lt;Widget&gt;[
                                    Expanded(
                                     child: Row(
                                       children: &lt;Widget&gt;[
                                         child: Padding(
                                           padding: const EdgeInsets.symmetric(horizontal: 8.0),
                                            child: Container(
                                              child: Column(
                                                children: &lt;Widget&gt;[
                                                  //THIS THE CONTAINER
                                                  new Container(. . .),
                                                  new Container(. . .)
  </code></pre>