行高展开时底部的位置图标

情况如何:

我希望它看起来怎么样:

我的简化代码:

Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: Colors.transparent,
      body: Column(
        children: <Widget>[
          Flexible(
            child: Container(),
          ),
          Container(
            decoration: BoxDecoration(
                color: Colors.white,
                borderRadius: BorderRadius.all(Radius.circular(20.0))),
            child: Row(
              children: <Widget>[
                IconButton(
                  onPressed: () {},
                  icon: Icon(Icons.camera_alt),
                  color: Colors.grey,
                ),
                Flexible(
                  child: TextField(
                    decoration: InputDecoration(
                      //Add th Hint text here.
                      hintText: "Digite sua mensagem",
                      border: OutlineInputBorder(),
                    ),
                    minLines: 1,
                    maxLines: 7,
                    controller: _textController,
                    onSubmitted: _handleSubmitted,
                  ),
                ),
                IconButton(
                  onPressed: () {},
                  icon: Icon(Icons.send),
                  color: Colors.grey,
                ),
              ],
            ),
          ),
        ],
      ),
    );
  }