参数类型“对象？”不能分配给参数类型“List<Employee>”

Question

child: FutureBuilder(
              future: employees,
              builder: (context, snapshot) {
                if (snapshot.hasData) {
                  return generateList(snapshot.data);
                }
                if (snapshot.data == null || snapshot.data.length == 0) {
                  return Text('No Employee Found');
                }
                return CircularProgressIndicator();
              },
            ),

错误参数类型“对象？”不能在下面的代码中分配给参数类型“列表”

return generateList(snapshot.data);

另一个错误无法无条件访问属性“长度”，因为接收者在代码中可以为“空”：

if (snapshot.data == null || snapshot.data.length == 0)

---

这里是 generateList 和 Employee 的代码 **************************************** ***

SingleChildScrollView generateList(List<Employee> employees) {
    return SingleChildScrollView(
      scrollDirection: Axis.vertical,
      child: SizedBox(
        width: MediaQuery.of(context).size.width,
        child: DataTable(
          columns: [
            DataColumn(
              label: Text('Name'),
            ),
            DataColumn(
              label: Text('Phome'),
            ),
            DataColumn(
              label: Text(''),
            )
          ],
          rows: employees
              .map(
                (employee) => DataRow(
              cells: [
                DataCell(
                  Text(employee.name),
                  onTap: () {
                    setState(() {
                      isUpdate = true;
                      employeeIdForUpdate = employee.id;
                    });
                    _employeeNameController.text = employee.name;
                    _employeePhoneController.text = employee.phone;
                  },
                ),
                DataCell(
                  Text(employee.phone),
                  onTap: () {
                    setState(() {
                      isUpdate = true;
                      employeeIdForUpdate = employee.id;
                    });
                    _employeeNameController.text = employee.name;
                    _employeePhoneController.text = employee.phone;
                  },
                ),
                DataCell(
                  IconButton(
                    icon: Icon(Icons.delete),
                    onPressed: () {
                      dbHelper.delete(employee.id);
                      refreshemployeeList();
                    },
                  ),
                )
              ],
            ),
          )
              .toList(),
        ),
      ),
    );
  }


class Employee {
  int id = 0;
  String name = "";
  String phone = "";
  Employee(this.id, this.name, this.phone);

  Map<String, dynamic> toMap() {
    var map = <String, dynamic>{
      'id': id,
      'name': name,
      'phone': phone,
    };
    return map;
  }

  Employee.fromMap(Map<String, dynamic> map) {
    id = map['id'];
    name = map['name'];
    phone = map['phone'];
  }
}

Answer 1

修改代码如下，

return generateList(List<Employee>.from(snapshot.data));

if (snapshot.data == null || snapshot.data!.length == 0)