Container(
         height: 50,
          // margin: EdgeInsets.only(top: 20),
          decoration: BoxDecoration(
              color: Colors.tealAccent,
              borderRadius: BorderRadius.circular(32)),
          child: TextFormField(
            cursorColor: Colors.black,
            // keyboardType: TextInputType.,
            decoration: InputDecoration(
              hintStyle: TextStyle(fontSize: 17),
              hintText: 'Search your trips',
              suffixIcon: Icon(Icons.search),
              border: InputBorder.none,
              contentPadding: EdgeInsets.all(18),
            ),
          ),
        ),

默认的

 Container(
      padding: const EdgeInsets.all(20),
      child: const TextField(
        decoration: InputDecoration(
            border: UnderlineInputBorder(), hintText: "Search Your tips"),
      ),
    ),

外框

 Container(
      padding: const EdgeInsets.all(20),
      child: TextField(
        decoration: InputDecoration(
          border: OutlineInputBorder(
            borderRadius: BorderRadius.circular(40),
          ),
          hintText: "Search Your tips",
        ),
      ),
    ),

没有边界

 Container(
      padding: const EdgeInsets.all(20),
      child: const TextField(
        decoration: InputDecoration(
            border: InputBorder.none, hintText: "Search Your tips"),
      ),
    ),

新的Flutter SDK，因为在集成了web和桌面支持之后，你需要像这样单独指定:

TextFormField(
  cursorColor: Colors.black,
  keyboardType: inputType,
  decoration: InputDecoration(
    border: InputBorder.none,
    focusedBorder: InputBorder.none,
    enabledBorder: InputBorder.none,
    errorBorder: InputBorder.none,
    disabledBorder: InputBorder.none,
    contentPadding:
      EdgeInsets.only(left: 15, bottom: 11, top: 11, right: 15),
    hintText: "Hint here"),
)

下面是一个补充答案，显示了一些更完整的代码:

  Container(
    decoration: BoxDecoration(
      color: Colors.tealAccent,
      borderRadius:  BorderRadius.circular(32),
    ),
    child: TextField(
      decoration: InputDecoration(
        hintStyle: TextStyle(fontSize: 17),
        hintText: 'Search your trips',
        suffixIcon: Icon(Icons.search),
        border: InputBorder.none,
        contentPadding: EdgeInsets.all(20),
      ),
    ),
  ),

注:

深色背景(代码未显示)是Colors.teal。 InputDecoration也有一个fill和fillColor属性，但是我不能让它们有一个角半径，所以我用一个容器代替。

decoration: InputDecoration(
 border:OutLineInputBorder(
 borderSide:BorderSide.none
 bordeRadius: BordeRadius.circular(20.0)
 )
)

删除下划线边框:InputBorder.none

对于提示，使用hintText: ' hintText '

   TextFormField(
      InputDecoration(
        border: InputBorder.none,
        hintText: 'Hint Text',
      ),
    ),