title: Move up floating action button
body: <p>I am adding animated icons in my floating action button at bottom navigation bar. But after adding 2 buttons my FAB moved down. </p>
  
  <p>I am using following code </p>
  
  <pre><code>Widget _buildCenterTab(){
      return new Column(
        mainAxisSize: MainAxisSize.min,
        children: new List.generate(icons.length, (int index) {
          Widget child = new Container(
            height: 56.0,
            width: 56.0,
            alignment: FractionalOffset.topCenter,
            child: new ScaleTransition(
              scale: new CurvedAnimation(
                parent: _controller,
                curve: new Interval(
                    0.0,
                    1.0 - index / icons.length / 2.0,
                    curve: Curves.easeOut
                ),
              ),
              child: new FloatingActionButton(
                heroTag: null,
                backgroundColor: blueColor,
                mini: true,
                child: new Icon(icons[index], color: Colors.white),
                onPressed: () {},
              ),
            ),
          );
          return child;
        }).toList()..add(
          new FloatingActionButton(
            heroTag: null,
            child: new AnimatedBuilder(
              animation: _controller,
              builder: (BuildContext context, Widget child) {
                return new Transform(
                  transform: new Matrix4.rotationZ(_controller.value * 0.5 * math.pi),
                  alignment: FractionalOffset.center,
                  child: new Icon(
                      _controller.isDismissed
                          ? Icons.add
                          : Icons.close),
                );
              },
            ),
            onPressed: () {
              if (_controller.isDismissed) {
                _controller.forward();
              } else {
                _controller.reverse();
              }
            },
          ),
        ),
      );
    }
  </code></pre>
  
  <p>Here is screenshot of my problem:
  <a href="https://i.stack.imgur.com/1jXTz.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/1jXTz.png" alt="enter image description here"></a></p>