flutter textfield设置高度后内容无法居中

Container( height: 50, width: MediaQuery.of(context).size.width * 2 / 3, alignment: Alignment.center, child: TextField( autofocus: true, decoration: InputDecoration( //这行代码是关键，设置这个之后，居中 contentPadding: EdgeInsets.all(2), hintText: '请输入手机号', prefixIcon: Icon(Icons.phone_android), border: OutlineInputBorder( borderSide: BorderSide(color: Colors.grey[600]), borderRadius: BorderRadius.circular(5), )), style: new TextStyle( color: Colors.black, fontSize: 16, ), maxLines: 1, textAlign: TextAlign.left, onChanged: (text) { //内容改变的回调 _phoneStr = text; print('change $_phoneStr'); }, onSubmitted: (text) { //内容提交(按回车)的回调 print('submit $text'); }, ), )