从TextinputType.text移到TextInputType.number时，数据将自动删除。在Flutter应用中

Question

从TextinputType.text移到TextInputType.number数据会自动删除。

class _StudentDetailsState extends State<StudentDetails> {
  TextEditingController adminNum,
      rollNum,
      nameOfstudent,
      dob,
      caste,
      bloodGroup,
      mobileNum,
      eMailId;
      var _formkey;
  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(
          title: Text('Student'),
        ),
        body: 
        ListView(
          padding: EdgeInsets.all(15.0),
          children: <Widget>[
            Padding(
              padding: EdgeInsets.only(top: 15.0, bottom: 15.0),
              child: TextField(
                controller: adminNum = new TextEditingController(),
                key: Key('Admn_Num'),
                autofocus: true,
                // onChanged: (value){},
                decoration: InputDecoration(
                    labelText: 'Admission Number',

                    border: OutlineInputBorder(
                      borderRadius: BorderRadius.circular(5.0),
                    )),
              ),
            ),
            Padding(
              padding: EdgeInsets.only(top: 15.0, bottom: 15.0),
              child: TextField(
                controller: rollNum = new TextEditingController(),
                key: Key('RollNo'),
                // onChanged: (value){},
                decoration: InputDecoration(
                    labelText: 'RollNo',

                    border: OutlineInputBorder(
                      borderRadius: BorderRadius.circular(5.0),
                    )),
              ),
            ),
            Padding(
              padding: EdgeInsets.only(top: 15.0, bottom: 15.0),
              child: TextField(
                controller: nameOfstudent = new TextEditingController(),
                key: Key('Name_of_Student'),
                // onChanged: (value){},
                decoration: InputDecoration(
                    labelText: 'Name',

                    border: OutlineInputBorder(
                      borderRadius: BorderRadius.circular(5.0),
                    )),
              ),
            ),
            Padding(
              padding: EdgeInsets.only(top: 15.0, bottom: 15.0),
              child: TextField(
                controller: dob = new TextEditingController(),
                key: Key('DOB'),
                keyboardType: TextInputType.datetime,
                // onChanged: (value){},
                decoration: InputDecoration(
                    labelText: 'DOB',

                    border: OutlineInputBorder(
                      borderRadius: BorderRadius.circular(5.0),
                    )),
              ),
            ),
            Padding(
              padding: EdgeInsets.only(top: 15.0, bottom: 15.0),
              child: TextField(
                controller: caste = new TextEditingController(),
                key: Key('Caste'),
                // onChanged: (value){},
                decoration: InputDecoration(
                    labelText: 'Caste (With FullName)',

                    border: OutlineInputBorder(
                      borderRadius: BorderRadius.circular(5.0),
                    )),
              ),
            ),
            Padding(
              padding: EdgeInsets.only(top: 15.0, bottom: 15.0),
              child: TextField(
                controller: bloodGroup = new TextEditingController(),
                key: Key('Blood_Group'),
                // onChanged: (value){},
                decoration: InputDecoration(
                    labelText: 'Blood Group',

                    border: OutlineInputBorder(
                      borderRadius: BorderRadius.circular(5.0),
                    )),
              ),
            ),
            Padding(
              padding: EdgeInsets.only(top: 15.0, bottom: 15.0),
              child: TextField(
                controller: mobileNum = new TextEditingController(),
                key: Key('Mobile_Num'),
                keyboardType: TextInputType.phone,
                // onChanged: (value){},
                decoration: InputDecoration(
                    labelText: 'Mobile Number',

                    border: OutlineInputBorder(
                      borderRadius: BorderRadius.circular(5.0),
                    )),
              ),
            ),
            Padding(
              padding: EdgeInsets.only(top: 15.0, bottom: 15.0),
              child: TextField(
                controller: eMailId = new TextEditingController(),
                key: Key('Mail_Id'),
                keyboardType: TextInputType.emailAddress,
                // onChanged: (value){},
                decoration: InputDecoration(
                    labelText: 'E-Mail Id',

                    border: OutlineInputBorder(
                      borderRadius: BorderRadius.circular(5.0),
                    )),
              ),
            ),
            Center(
              child: ButtonTheme(
                minWidth: 100.0,
                child: OutlineButton(
                  padding: EdgeInsets.only(left: 25, right: 25),
                  child: Text('Submit'),
                  textTheme: ButtonTextTheme.primary,
                  onPressed: () {},
                ),
              ),
            )
          ],
        ));
  }
}

问题是，当我在“名称”文本字段中输入具有TextInputType.text的内容，然后点击另一个具有TextInputType.number的文本字段时，“名称”字段会被清除，没有明显的原因