如何在flutter中更改底部表单对话框中的文本？

showModalBottomSheet(
  context: context,
  builder: (BuildContext context) {
    return Container(
      child: Column(
        children: [
          // 表单字段
          TextField(
            controller: _textEditingController,
            decoration: InputDecoration(
              labelText: '文本',
            ),
          ),
          // 其他表单字段...
        ],
      ),
    );
  },
);

TextEditingController _textEditingController = TextEditingController();

FlatButton(
  onPressed: () {
    String text = _textEditingController.text;
    // 处理文本
  },
  child: Text('保存'),
),