在SearchDelegate中重写appBarTheme

class CustomSearchDelegate extends SearchDelegate<String> {
  @override
  ThemeData appBarTheme(BuildContext context) {
    final ThemeData theme = Theme.of(context);
    return theme.copyWith(
      appBarTheme: AppBarTheme(
        color: Colors.blue, // 自定义AppBar的背景颜色
        textTheme: TextTheme(
          headline6: TextStyle(
            color: Colors.white, // 自定义AppBar标题的文字颜色
          ),
        ),
        iconTheme: IconThemeData(
          color: Colors.white, // 自定义AppBar图标的颜色
        ),
      ),
    );
  }

  // 其他重写方法...
}