当输入文本时自动展开的Flutter文本字段，当达到一定高度时开始滚动文本

Container(    child: new ConstrainedBox(        constraints: BoxConstraints( maxHeight: 300.0,        ),        child: TextField(         maxLines: null,     ), ),        ),    ),)

在较旧的Flutter版本中，

Container(    child: new ConstrainedBox(        constraints: BoxConstraints( maxHeight: 300.0,        ),        child: new Scrollbar( child: new SingleChildScrollView(     scrollDirection: Axis.vertical,     reverse: true,     child: new TextField(         maxLines: null,     ), ),        ),    ),)