在运行时更改应用主题

Question

我是 Flutter 的初学者。 如何将整个应用程序主题从浅色主题更改为深色主题？

假设我有以下 Light Theme 的代码：

final ThemeData dTheme = new ThemeData(
  primarySwatch: Colors.orange,
  primaryColor: Colors.orangeAccent[100],
  primaryColorBrightness: Brightness.light,
);

和黑暗主题：

final ThemeData lTheme = new ThemeData(
  primarySwatch: Colors.indigo,
  primaryColor: Colors.indigoAccent[100],
  primaryColorBrightness: Brightness.dark,
);

我想在运行时点击按钮更改主题。

Answer 1

这是此处回答的问题的具体案例：Force Flutter to redraw all widgets

看看那个问题中提到的股票样本，特别注意： https://github.com/flutter/flutter/blob/master/examples/stocks/lib/main.dart https://github.com/flutter/flutter/blob/master/examples/stocks/lib/stock_settings.dart

注意以下几点：

1. 主题由_configuration指定，由configurationUpdater更新
2. configurationUpdater 传递给需要它的应用的子级
3. 孩子们可以调用该 configurationUpdater，这反过来会在应用的根目录设置状态，进而使用指定的主题重绘应用

以下代码可能对您有所帮助：

// How to use: Any Widget in the app can access the ThemeChanger
// because it is an InheritedWidget. Then the Widget can call
// themeChanger.theme = [blah] to change the theme. The ThemeChanger
// then accesses AppThemeState by using the _themeGlobalKey, and
// the ThemeChanger switches out the old ThemeData for the new
// ThemeData in the AppThemeState (which causes a re-render).

final _themeGlobalKey = new GlobalKey(debugLabel: 'app_theme');

class AppTheme extends StatefulWidget {

  final child;

  AppTheme({
    this.child,
  }) : super(key: _themeGlobalKey);

  @override
  AppThemeState createState() => new AppThemeState();
}

class AppThemeState extends State<AppTheme> {

  ThemeData _theme = DEV_THEME;

  set theme(newTheme) {
    if (newTheme != _theme) {
      setState(() => _theme = newTheme);
    }
  }

  @override
  Widget build(BuildContext context) {
    return new ThemeChanger(
      appThemeKey: _themeGlobalKey,
      child: new Theme(
        data: _theme,
        child: widget.child,
      ),
    );
  }
}

class ThemeChanger extends InheritedWidget {

  static ThemeChanger of(BuildContext context) {
    return context.inheritFromWidgetOfExactType(ThemeChanger);
  }

  final ThemeData theme;
  final GlobalKey _appThemeKey;

  ThemeChanger({
    appThemeKey,
    this.theme,
    child
  }) : _appThemeKey = appThemeKey, super(child: child);

  set appTheme(AppThemeOption theme) {
    switch (theme) {
      case AppThemeOption.experimental:
        (_appThemeKey.currentState as AppThemeState)?.theme = EXPERIMENT_THEME;
        break;
      case AppThemeOption.dev:
        (_appThemeKey.currentState as AppThemeState)?.theme = DEV_THEME;
        break;
    }
  }

  @override
  bool updateShouldNotify(ThemeChanger oldWidget) {
    return oldWidget.theme == theme;
  }

}