我只需要将小部件 Package 在一个中心小部件中，并使用mainAxisAlignment

return Scaffold(
  appBar: AppBar(
    title: Center(
      child: Row(
        mainAxisAlignment: MainAxisAlignment.center,
        children: [
          IconButton(
            icon: Icon(Icons.arrow_back),
            onPressed: () {
              // do something when the back arrow button is tapped
            },
            color: Colors.black,
          ),
          Text(
            'Today',
            style: TextStyle(
              color: Colors.black, // set the color of the title text
            ),
          ),
          IconButton(
            icon: Icon(Icons.arrow_forward),
            onPressed: () {
              // do something when the forward arrow button is tapped
            },
            color: Colors.black,
          ),
        ],
      ),
    ),
    backgroundColor: Theme.of(context).scaffoldBackgroundColor,
    centerTitle: true,
    leading: IconButton(
      icon: Icon(
        Icons.menu,
        color: Colors.black,
      ),
      onPressed: () {},
    ),
    actions: [
      Padding(
        padding: EdgeInsets.only(
            right: 12.0), // set the horizontal padding to 16.0
        child: IconButton(
          icon: Icon(
            Icons.settings,
            color: Colors
                .black, // set the color of the search icon button to white
          ),
          onPressed: () {},
        ),
      ),
    ],
    elevation: 0,
  ),

有两种可能的解决方案：

Row(
   mainAxisAlignment: MainAxisAlignment.center,
   children: [...]
 );

或

Row(
   mainAxisSize: MainAxisSize.min,
   children: [...]
 );