Flutter Dart报错Map<dynamic, dynamic>无法赋值给Map<int, Color>如何解决

原因 #

• MaterialColor构造函数要求传入的色板参数类型为Map<int, Color>，但你声明swatch变量时仅写了Map swatch，未指定泛型，Dart会将该变量推断为Map<dynamic, dynamic>，类型不匹配触发报错。

解决方法 #

仅需修改swatch变量的声明，显式指定泛型即可，两种写法均可生效：

1. 显式标注变量泛型类型

Map<int, Color> swatch = <int, Color>{};

2. 用final关键字让Dart自动推断右侧初始化值的泛型类型，写法更简洁

final swatch = <int, Color>{};

优化后的完整代码 #

import 'package:flutter/material.dart';

class WpCreateColor {
  final Color wpColor = const Color.fromARGB(255, 77, 203, 79);

  MaterialColor createMaterialColor() {
    final strengths = <double>[.05];
    // 修正swatch的类型声明
    final swatch = <int, Color>{};
    final int r = wpColor.red, g = wpColor.green, b = wpColor.blue;

    for (int i = 1; i < 10; i++) {
      strengths.add(0.1 * i);
    }
    // 此处改用官方更推荐的for-in循环替代forEach，非必须修改
    for (final strength in strengths) {
      final double ds = 0.5 - strength;
      swatch[(strength * 1000).round()] = Color.fromRGBO(
        r + ((ds < 0 ? r : (255 - r)) * ds).round(),
        g + ((ds < 0 ? g : (255 - g)) * ds).round(),
        b + ((ds < 0 ? b : (255 - b)) * ds).round(),
        1,
      );
    }
    return MaterialColor(wpColor.value, swatch);
  }
}

内容的提问来源于stack exchange，提问作者edn