Flutter更改主题颜色报错:type ‘Color‘ is not a subtype of type ‘MaterialColor‘

Bertha 。 2022-10-28 14:23 170阅读 0赞

class MyApp extends StatelessWidget { 
      @override
      Widget build(BuildContext context) { 
        return MaterialApp(
          title: 'Futter App',
          debugShowCheckedModeBanner: false,
          theme: ThemeData(
          	//更改主题色为白色
            primarySwatch: Colors.white,
            visualDensity: VisualDensity.adaptivePlatformDensity,
          ),
          home: SplashPage(),
        );
      }
    }

在Flutter中，如果我们把默认主题色更改为白色(Colors.white)或黑色(Colors.black)，会发生以下错误：

I/flutter ( 6397): ══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY╞═══════════════════════════════════════════════════════════
        I/flutter ( 6397): The following assertion was thrown attaching to the render tree:
        I/flutter ( 6397): type 'Color' is not a subtype of type 'MaterialColor'
        I/flutter ( 6397): Either the assertion indicates an error in the framework itself, or we should provide 
        substantially
        I/flutter ( 6397): more information in this error message to help you determine and fix the underlying cause.
        I/flutter ( 6397): In either case, please report this assertion by filing a bug on GitHub:
        I/flutter ( 6397):   https://github.com/flutter/flutter/issues/new

## 原因 ##

查看错误提示，说的是Color不是MaterialColor的子类，打开ThemeData的源码发现，primarySwatch是一个MaterialColor类型的变量，而MaterialColor继承自ColorSwatch。  
源码如下

/// A color that has a small table of related colors called a "swatch".
    ///
    /// The table is indexed by values of type `T`.
    ///
    /// See also:
    ///
    ///  * [MaterialColor] and [MaterialAccentColor], which define material design
    ///    primary and accent color swatches.
    ///  * [material.Colors], which defines all of the standard material design
    ///    colors.
    @immutable
    class ColorSwatch<T> extends Color {
      /// Creates a color that has a small table of related colors called a "swatch".
      ///
      /// The `primary` argument should be the 32 bit ARGB value of one of the
      /// values in the swatch, as would be passed to the [new Color] constructor
      /// for that same color, and as is exposed by [value]. (This is distinct from
      /// the specific index of the color in the swatch.)
      const ColorSwatch(int primary, this._swatch) : super(primary);
    
      @protected
      final Map<T, Color> _swatch;
    
      /// Returns an element of the swatch table.
      Color? operator [](T index) => _swatch[index];
    
      @override
      bool operator ==(Object other) {
        if (identical(this, other))
          return true;
        if (other.runtimeType != runtimeType)
          return false;
        return super == other
            && other is ColorSwatch<T>
            && mapEquals<T, Color>(other._swatch, _swatch);
      }
    
      @override
      int get hashCode => hashValues(runtimeType, value, _swatch);
    
      @override
      String toString() => '${objectRuntimeType(this, 'ColorSwatch')}(primary value: ${super.toString()})';
    }

为什么Colors.blue或者其它颜色可以使用呢？  
查看Colors的源码发现，white和black其它颜色都是MaterialColor类型。

static const Color black = Color(0xFF000000);
      static const Color white = Color(0xFFFFFFFF);
      static const MaterialColor blue = MaterialColor(
        _bluePrimaryValue,
        <int, Color>{ 
           50: Color(0xFFE3F2FD),
          100: Color(0xFFBBDEFB),
          200: Color(0xFF90CAF9),
          300: Color(0xFF64B5F6),
          400: Color(0xFF42A5F5),
          500: Color(_bluePrimaryValue),
          600: Color(0xFF1E88E5),
          700: Color(0xFF1976D2),
          800: Color(0xFF1565C0),
          900: Color(0xFF0D47A1),
        },
      );

## 解决方法 ##

到这里我们知道了，必须传入一个MaterialColor类型的变量才行，既然Flutter没有提供，那我们自己模仿创建一个即可。

void main() { 
      runApp(MyApp());
    }
    
    const MaterialColor white = const MaterialColor(
      0xFFFFFFFF,
      const <int, Color>{ 
        50: const Color(0xFFFFFFFF),
        100: const Color(0xFFFFFFFF),
        200: const Color(0xFFFFFFFF),
        300: const Color(0xFFFFFFFF),
        400: const Color(0xFFFFFFFF),
        500: const Color(0xFFFFFFFF),
        600: const Color(0xFFFFFFFF),
        700: const Color(0xFFFFFFFF),
        800: const Color(0xFFFFFFFF),
        900: const Color(0xFFFFFFFF),
      },
    );
    const MaterialColor black = const MaterialColor(
      0xFFFFFFFF,
      const <int, Color>{ 
        50: const Color(0xFF000000),
        100: const Color(0xFF000000),
        200: const Color(0xFF000000),
        300: const Color(0xFF000000),
        400: const Color(0xFF000000),
        500: const Color(0xFF000000),
        600: const Color(0xFF000000),
        700: const Color(0xFF000000),
        800: const Color(0xFF000000),
        900: const Color(0xFF000000),
      },
    );
    
    class MyApp extends StatelessWidget { 
      MyApp() { 
        final router = FluroRouter();
        Routes.configureRoutes(router);
        Application.router = router;
      }
    
      @override
      Widget build(BuildContext context) { 
        return MaterialApp(
          title: 'Flutter App',
          debugShowCheckedModeBanner: false,
          theme: ThemeData(
            primarySwatch: white,
          ),
          home: SplashPage(),
        );
      }
    }