I have an error: A value of type 'Color' can't be assigned to a variable of type 'MaterialColor' in line with code: selectedValue = newValue!. Please help me solve it. I am attaching the screen code:

class _ColorPickerWidgetState extends State<ColorPickerWidget> {
  List<DropdownMenuItem<Color>> get dropdownItems{
    List<DropdownMenuItem<Color>> colorItems = [
      const DropdownMenuItem(
        value: Colors.yellow,
        child: Text('Yellow'),
      ),
      const DropdownMenuItem(
        value: Colors.red,
          child: Text('Red'),
      ),
    ];
    return colorItems;
  }

  // default value of select
    MaterialColor selectedValue = Colors.yellow;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Choose a color'),
        centerTitle: true,
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            DropdownButton<Color>(
            value: selectedValue,
            items: dropdownItems,
              onChanged: (Color? newValue){
              setState(() {
                selectedValue = newValue!;
              });
            },
            ),
            ElevatedButton(onPressed: () => _changeColor(selectedValue),
                child: const Text('Next'),
            ),
          ],
        ),
      ),
    );
  }
}

CodePudding user response：

Change:

MaterialColor selectedValue = Colors.yellow;

To:

Color selectedValue = Colors.yellow;

While MaterialColor extends ColorSwatch which extends Color, you cannot assign a Color (which might not be a MaterialColor) to MaterialColor

CodePudding user response：

There are 2 two solutions

1. Maintain only MaterialColor type in all places

class ColorPickerWidget extends StatefulWidget {
  const ColorPickerWidget({Key? key}) : super(key: key);

  @override
  State<ColorPickerWidget> createState() => _ColorPickerWidgetState();
}

class _ColorPickerWidgetState extends State<ColorPickerWidget> {
  List<DropdownMenuItem<MaterialColor>> get dropdownItems {
    List<DropdownMenuItem<MaterialColor>> colorItems = [
      const DropdownMenuItem(
        value: Colors.yellow,
        child: Text('Yellow'),
      ),
      const DropdownMenuItem(
        value: Colors.red,
        child: Text('Red'),
      ),
    ];
    return colorItems;
  }

  // default value of select
  MaterialColor selectedValue = Colors.yellow;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Choose a color'),
        centerTitle: true,
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            DropdownButton<MaterialColor>(
              value: selectedValue,
              items: dropdownItems,
              onChanged: (MaterialColor? newValue) {
                setState(() {
                  selectedValue = newValue!;
                });
              },
            ),
            ElevatedButton(
              onPressed: () => _changeColor(selectedValue),
              child: const Text('Next'),
            ),
          ],
        ),
      ),
    );
  }
}

2. Maintain only the Color type in all places

class ColorPickerWidget extends StatefulWidget {
  const ColorPickerWidget({Key? key}) : super(key: key);

  @override
  State<ColorPickerWidget> createState() => _ColorPickerWidgetState();
}

class _ColorPickerWidgetState extends State<ColorPickerWidget> {
  List<DropdownMenuItem<Color>> get dropdownItems {
    List<DropdownMenuItem<Color>> colorItems = [
      const DropdownMenuItem(
        value: Colors.yellow,
        child: Text('Yellow'),
      ),
      const DropdownMenuItem(
        value: Colors.red,
        child: Text('Red'),
      ),
    ];
    return colorItems;
  }

  // default value of select
  Color selectedValue = Colors.yellow;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Choose a color'),
        centerTitle: true,
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            DropdownButton<Color>(
              value: selectedValue,
              items: dropdownItems,
              onChanged: (Color? newValue) {
                setState(() {
                  selectedValue = newValue!;
                });
              },
            ),
            ElevatedButton(
              onPressed: () => _changeColor(selectedValue),
              child: const Text('Next'),
            ),
          ],
        ),
      ),
    );
  }
}