Flutter Custom Animated Icon

You're in luck my friend! Flutter already has you covered with AnimatedIcon()

AnimatedIcon Class in the docs

Animated Icon Widget of the week Video

Now to animate your Icons with Flare. Jeff Delaney made a good tutorial for this.

https://fireship.io/lessons/animated-navigation-flutter-flare/

I know it's not as beautiful as AnimatedIcon, but you could actually get very similar transition with any 2 icons of your choice with just a few lines of code:

 IconButton(
      icon: AnimatedSwitcher(
          duration: const Duration(milliseconds: 300),
          transitionBuilder: (child, anim) => RotationTransition(
                turns: child.key == ValueKey('icon1')
                    ? Tween<double>(begin: 1, end: 0.75).animate(anim)
                    : Tween<double>(begin: 0.75, end: 1).animate(anim),
                child: FadeTransition(opacity: anim, child: child),
              ),
          child: _currIndex == 0
              ? Icon(Icons.close, key: const ValueKey('icon1'))
              : Icon(
                  Icons.arrow_back,
                  key: const ValueKey('icon2'),
                )),
      onPressed: () {
        setState(() {
          _currIndex = _currIndex == 0 ? 1 : 0;
        });
      },
    );

Result:

---

Or you can use ScaleTransition instead of FadeTransition, and get even more similar animation:

IconButton(
      icon: AnimatedSwitcher(
          duration: const Duration(milliseconds: 350),
          transitionBuilder: (child, anim) => RotationTransition(
                turns: child.key == ValueKey('icon1')
                    ? Tween<double>(begin: 1, end: 0.75).animate(anim)
                    : Tween<double>(begin: 0.75, end: 1).animate(anim),
                child: ScaleTransition(scale: anim, child: child),
              ),
          child: _currIndex == 0
              ? Icon(Icons.close, key: const ValueKey('icon1'))
              : Icon(
                  Icons.arrow_back,
                  key: const ValueKey('icon2'),
                )),
      onPressed: () {
        setState(() {
          _currIndex = _currIndex == 0 ? 1 : 0;
        });
      },
    )

Result:

---

With this approach you could use any icons you want, and it doesn't require creating separate AnimationController just to control the transition, unlike AnimatedIcon