Flutter 尽管海拔设置为 0，如何删除 appBar 下的下划线

我想删除AppBar下面的蓝线.

What have I tried already?个

1.更改appBar backgroundColor: kTextfieldBorderColor,的 colored颜色

2.我已将标高设置为0elevation: 0

3.回顾这个类似的问题here，但它没有给出任何令人满意的答案，而只是暂时的解决方案.edit:我try 了这里提到的解决方案，但将Scaffold和appBar都设置为透明并不起作用

4.我还try 在appBar中添加toolbarHeight: kToolbarHeight + 1.25,，但这甚至都不起作用.

下面我添加了完整的脚手架代码，让你知道为什么它会导致这个问题.

Widget build(BuildContext context) {
return Scaffold(
  backgroundColor: kBackgroundColor,
  appBar: AppBar(
    backgroundColor: kTextfieldBorderColor,
    elevation: 0,
    // leading: null,
    actions: <Widget>[
      IconButton(
          icon: Icon(Icons.close),
          onPressed: () {
            //Implement logout functionality
            _auth.signOut();
            Navigator.pop(context);
          }),
    ],
    title: Text('⚡️Chat'),
  ),
  body: SafeArea(
    child: Column(
      mainAxisAlignment: MainAxisAlignment.spaceBetween,
      crossAxisAlignment: CrossAxisAlignment.stretch,
      children: <Widget>[
        Container(
          decoration: kMessageContainerDecoration,
          child: Row(
            crossAxisAlignment: CrossAxisAlignment.center,
            children: <Widget>[
              Expanded(
                child: TextField(
                  onChanged: (value) {
                    //Do something with the user input.
                  },
                  decoration: kMessageTextFieldDecoration,
                  cursorColor: kTextfieldBorderColor,
                ),
              ),
              TextButton(
                onPressed: () {
                  //Implement send functionality.
                },
                child: const Text(
                  'Send',
                  style: kSendButtonTextStyle,
                ),
              ),
            ],
          ),
        ),
      ],
    ),
  ),
);

用于 colored颜色 、文本字段等的代码为constants

const kBackgroundColor = Color(0xffEDD9C8);
const kRoundedButtonColor = Color(0xffC68E5D);
const kTextfieldBorderColor = Color(0xffC68E5D);
const kMessageTextFieldDecoration = InputDecoration(
  contentPadding: EdgeInsets.symmetric(vertical: 10.0, horizontal: 20.0),
  hintText: 'Type your message here...',
  border: InputBorder.none,
);

const kMessageContainerDecoration = BoxDecoration(
  border: Border(
    top: BorderSide(color: Colors.lightBlueAccent, width: 2.0),
  ),
);