如何动态改变FloatingActionButton的颜色？

Question

如何动态更改FloatingActionButton的颜色？我想这样但这是行不通的。如何运作？

Color _background = Colors.white;
Color _foreground = Colors.green[900];
FloatingActionButton(
                    heroTag: null,
                    elevation: 10.0,
                    onPressed: () {
                      setState(() {
                        _background = _foreground;
                      });
                    },
                    child: Icon(Icons.directions_walk, color: _foreground),
                    backgroundColor: _background,
                  ),

Answer 1

您的代码实际上应该没问题，我认为问题在于您的变量

Color _background = Colors.white;
Color _foreground = Colors.green[900];

在您的构建函数中。

例如：

这行不通

class _MyAppState extends State<MyApp> {
  @override
  Widget build(BuildContext context) {
    Color _background = Colors.white;
    Color _foreground = Colors.green[900];
    return Scaffold(
        floatingActionButton: FloatingActionButton(
          heroTag: null,
          elevation: 10.0,
          onPressed: () {
            setState(() {
              _background = _foreground;
            });
          },
          child: Icon(Icons.directions_walk, color: _foreground),
          backgroundColor: _background,
        ),
        body: Text("Hello"));
  }
}

这将起作用

class _MyAppState extends State<MyApp> {
  Color _background = Colors.white;
  Color _foreground = Colors.green[900];
  @override
  Widget build(BuildContext context) {
    return Scaffold(
        floatingActionButton: FloatingActionButton(
          heroTag: null,
          elevation: 10.0,
          onPressed: () {
            setState(() {
              _background = _foreground;
            });
          },
          child: Icon(Icons.directions_walk, color: _foreground),
          backgroundColor: _background,
        ),
        body: Text("Hello"));
  }
}

但是它不会切换背景颜色，此代码只能更改一次颜色。