title: How to add a widget by position on runtime in flutter?
body: <p>I am trying to add a button on an image on tap position.
  I have managed to get position on tap by using onTapUp's detail parameter.</p>
  
  <p>However, I can't add an icon button when user taps on the image.</p>
  
  <p>Below code shows my sample.</p>
  
  <pre><code>class ArticlesShowcase extends StatelessWidget {
    final commentWidgets = List&lt;Widget&gt;();
    @override
    Widget build(BuildContext context) {
      return new GestureDetector(
            child: new Center(
              child: Image.network(
                'https://via.placeholder.com/300x500',
              ),
            ),
            onTapUp: (detail) {
              final snackBar = SnackBar(
                  content: Text(detail.globalPosition.dx.toString() +
                      " " +
                      detail.globalPosition.dy.toString()));
              Scaffold.of(context).showSnackBar(snackBar);
              new Offset(detail.globalPosition.dx, detail.globalPosition.dy);
              var btn = new RaisedButton(
                onPressed: () =&gt; {},
                color: Colors.purple,
                child: new Text(
                  "Book",
                  style: new TextStyle(color: Colors.white),
                ),
              );
              commentWidgets.add(btn);
            },
          );          
    }
  }
  </code></pre>
  
  <p>I tried to add the button on the list but no chance.</p>