我已经创建了一个学生注册的课程列表。但是，我不知道如何从Main中的列表访问对象。下面，我试图获得Student-Id并从那里提取信息，但它不起作用。我是新来的编码，请帮助
using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Threading.Tasks;
namespace Jvstt_College
{
class Admin
{
##
## Dictionary<int, Student> studentList = new Dictionary<int, Student>();
Dictionary<int, Professor> professorList = new Dictionary<int, Professor>();
List<Course> courseList = new List<Course>();
Dictionary<int, Student> studentCourses = new Dictionary<int, Student>();
public Dictionary<int, Student> StudentList()
{
var Student1 = new Student() { FirstName = "Tom", LastName = " Jones", Password = "Test", EnrollmentId = 111111};
var Student2 = new Student() { FirstName = "Mark", LastName = " Thomas", Password = "Grace", EnrollmentId = 101203 };
var Student3 = new Student() { FirstName = "Jake", LastName = " Riley", Password = "SavedbyChrist1", EnrollmentId = 568903 };
var Student4 = new Student() { FirstName = "Olivia", LastName = " Beckam", Password = "GodisGood", EnrollmentId = 951357 };
var Student5 = new Student() { FirstName = "Myrai", LastName = " Bailey", Password = "ChildofGod", EnrollmentId = 741369 };
var Student6 = new Student() { FirstName = "Majea", LastName = " Bailey", Password = "CoastLand", EnrollmentId = 852146 };
studentList.Add(111111, Student1);
studentList.Add(101203, Student2);
studentList.Add(568903, Student3);
studentList.Add(951357, Student4);
studentList.Add(741369, Student5);
studentList.Add(852146, Student6);
return studentList;
}
public Dictionary<int, Professor> ProfessorList()
{
professorList.Add(654321, new Professor { FirstName = "Grace", LastName = "Riley", Password = "Gracey1983", EnrollmentId = 654321 });
enter code here professorList.Add(852963, new Professor { FirstName = "Liam", LastName = "Beckam", Password = "Password", EnrollmentId = `enter code here`852963 });
professorList.Add(359861, new Professor { FirstName = "Martha", LastName = "Hart", Password = "QwertYy00", EnrollmentId = 359861 });
professorList.Add(612832, new Professor { FirstName = "George", LastName = "Washington", Password = "Kid$nExtD00r", EnrollmentId = 612832 });
return professorList;
}
public List<Course> CourseList()
{
var Accounts = new Course() { CourseID = 101, CourseName = " Accounts " };
var Bio_Psychology = new Course() { CourseID = 102, CourseName = " Bio_Psychology " };
var Business = new Course() { CourseID = 103, CourseName = " Business " };
var Chemistry = new Course() { CourseID = 104, CourseName = " Chemistry " };
var CSWDCA = new Course() { CourseID = 105, CourseName = " Computer Science/Web Design/Cybersecurity Accounts" };
var Psychology = new Course() { CourseID = 106, CourseName = " Psychology " };
var Statistics = new Course() { CourseID = 107, CourseName = " Statistics " };
var Advance_Math = new Course() { CourseID = 108, CourseName = "Advance Math" };
courseList.Add(Accounts);
courseList.Add(Bio_Psychology);
courseList.Add(Business);
courseList.Add(Chemistry);
courseList.Add(CSWDCA);
courseList.Add(Psychology);
courseList.Add(Statistics);
courseList.Add(Advance_Math);
return courseList;
}
public Dictionary<int, Student> StudentEnrollments()
{
var Student1 = studentList[111111];
{
if(Student1.Courses == null)
{
Student1.Courses = new List<Course>();
Student1.Courses?.Add(courseList[0]);
Student1.Courses?.Add(courseList[2]);
Student1.Courses?.Add(courseList[4]);
}
}
var Student2 = studentList[101203];
{
if(Student2.Courses == null)
{
Student2.Courses = new List<Course>();
Student2.Courses?.Add(courseList[1]);
Student2.Courses?.Add(courseList[4]);
Student2.Courses?.Add(courseList[5]);
Student2.Courses?.Add(courseList[6]);
Student2.Courses?.Add(courseList[7]);
}
}
var Student3 = studentList[568903];
{
if (Student3.Courses == null)
{
Student3.Courses = new List<Course>();
Student3.Courses?.Add(courseList[1]);
Student3.Courses?.Add(courseList[4]);
}
}
var Student4 = studentList[951357];
{
if (Student4.Courses == null)
{
Student4.Courses = new List<Course>();
Student4.Courses?.Add(courseList[1]);
Student4.Courses?.Add(courseList[5]);
Student4.Courses?.Add(courseList[7]);
}
}
var Student5 = studentList[741369];
{
if (Student5.Courses == null)
{
Student5.Courses = new List<Course>();
Student5.Courses?.Add(courseList[0]);
Student5.Courses?.Add(courseList[2]);
Student5.Courses?.Add(courseList[3]);
Student5.Courses?.Add(courseList[6]);
Student5.Courses?.Add(courseList[7]);
}
}
var Student6 = studentList[852146];
{
if (Student6.Courses == null)
{
Student6.Courses = new List<Course>();
Student6.Courses?.Add(courseList[0]);
Student6.Courses?.Add(courseList[1]);
Student6.Courses?.Add(courseList[2]);
Student6.Courses?.Add(courseList[3]);
Student6.Courses?.Add(courseList[4]);
Student6.Courses?.Add(courseList[5]);
Student6.Courses?.Add(courseList[6]);
}
}
studentCourses.Add(111111,Student1);
studentCourses.Add(101203,Student2);
studentCourses.Add(568903,Student3);
studentCourses.Add(951357,Student4);
studentCourses.Add(741369,Student5);
studentCourses.Add(852146,Student6);
return studentCourses;
}
}
}
}
首先声明Professor,Student和Course类。由于Professor和Student具有相似的属性，并且它们都是人，因此从抽象的Person类派生它们是有意义的。抽象类不能被实例化。
abstract class Person
{
public string FirstName { get; set; }
public string LastName { get; set; }
public string Password { get; set; }
public int EnrollmentId { get; set; }
}
class Professor : Person
{
}
class Student : Person
{
public List<Course> Courses { get; } = new List<Course>();
}
class Course
{
public int CourseID { get; set; }
public string CourseName { get; set; }
}
在Student类中，我将Courses列表创建为只读属性，并使用属性初始化器对其进行初始化。这样可以避免以后执行if (Student2.Courses == null) { Student2.Courses = new List<Course>(); ... }之类的操作。
你有几个初始化列表和字典的方法。它们应该声明并创建它们返回的集合。否则，如果在周围作用域中声明集合，则不需要返回语句，并且职责也不明确。加上也，字典不是一个列表。由于这些方法不再依赖于实例字段，我们将它们设置为静态(并简化它们):
// In class Admin
private static Dictionary<int, Student> CreateStudents()
{
return new Dictionary<int, Student> {
{ 111111, new Student { FirstName = "Tom", LastName = " Jones", Password = "Test", EnrollmentId = 111111 } },
{ 101203, new Student { FirstName = "Mark", LastName = " Thomas", Password = "Grace", EnrollmentId = 101203 } },
{ 568903, new Student { FirstName = "Jake", LastName = " Riley", Password = "SavedbyChrist1", EnrollmentId = 568903 } },
{ 951357, new Student { FirstName = "Olivia", LastName = " Beckam", Password = "GodisGood", EnrollmentId = 951357 } },
{ 741369, new Student { FirstName = "Myrai", LastName = " Bailey", Password = "ChildofGod", EnrollmentId = 741369 } },
{ 852146, new Student { FirstName = "Majea", LastName = " Bailey", Password = "CoastLand", EnrollmentId = 852146 } }
};
}
private static Dictionary<int, Professor> CreateProfessors()
{
return new Dictionary<int, Professor> {
{ 654321, new Professor { FirstName = "Grace", LastName = "Riley", Password = "Gracey1983", EnrollmentId = 654321 } },
{ 852963, new Professor { FirstName = "Liam", LastName = "Beckam", Password = "Password", EnrollmentId = 852963 } },
{ 359861, new Professor { FirstName = "Martha", LastName = "Hart", Password = "QwertYy00", EnrollmentId = 359861 } },
{ 612832, new Professor { FirstName = "George", LastName = "Washington", Password = "Kid$nExtD00r", EnrollmentId = 612832 } }
};
}
private static List<Course> CreateCourses()
{
return new List<Course> {
new Course { CourseID = 101, CourseName = "Accounts" },
new Course { CourseID = 102, CourseName = "Bio_Psychology" },
new Course { CourseID = 103, CourseName = "Business" },
new Course { CourseID = 104, CourseName = "Chemistry" },
new Course { CourseID = 105, CourseName = "Computer Science/Web Design/Cybersecurity Accounts" },
new Course { CourseID = 106, CourseName = "Psychology" },
new Course { CourseID = 107, CourseName = "Statistics" },
new Course { CourseID = 108, CourseName = "Advance Math" }
};
}
class Admin
{
public readonly Dictionary<int, Student> students = CreateStudents();
public readonly Dictionary<int, Professor> professors = CreateProfessors();
public readonly List<Course> courses = CreateCourses();
...
}
我将它们设置为只读。这只意味着以后不能为它分配另一个集合。集合本身仍然是读/写的。
我们不需要另一个studentCourses集合，我们可以直接在现有的students字典中添加课程给学生。
如果我们在类Admin中声明一个实例方法EnrollStudents，那么它可以访问该类的字段。
public void EnrollStudents()
{
Student student = students[111111];
student.Courses.Add(courses[0]);
student.Courses.Add(courses[2]);
student.Courses.Add(courses[4]);
student = students[101203]; // It is okay to reuse the student variable
student.Courses.Add(courses[1]);
student.Courses.Add(courses[4]);
student.Courses.Add(courses[5]);
student.Courses.Add(courses[6]);
student.Courses.Add(courses[7]);
student = students[568903];
student.Courses.Add(courses[1]);
student.Courses.Add(courses[4]);
student = students[951357];
student.Courses.Add(courses[1]);
student.Courses.Add(courses[5]);
student.Courses.Add(courses[7]);
student = students[741369];
student.Courses.Add(courses[0]);
student.Courses.Add(courses[2]);
student.Courses.Add(courses[3]);
student.Courses.Add(courses[6]);
student.Courses.Add(courses[7]);
student = students[852146];
student.Courses.Add(courses[0]);
student.Courses.Add(courses[1]);
student.Courses.Add(courses[2]);
student.Courses.Add(courses[3]);
student.Courses.Add(courses[4]);
student.Courses.Add(courses[5]);
student.Courses.Add(courses[6]);
}
注意，我们不需要返回任何东西。由于类是引用类型，原始students字典中的所有学生现在都被课程更新了。当然，我们必须在某个地方调用这个方法(可能在Main中)。
但是我们可以用一个新的辅助方法来简化这个方法，因为我们有很多重复的地方可以避免:
private void AddStudentCourses(Student student, params int[] courseIndexes)
{
foreach (int index in courseIndexes) {
student.Courses.Add(courses[index]);
}
}
public void EnrollStudents()
{
AddStudentCourses(students[111111], 0, 2, 4);
AddStudentCourses(students[101203], 1, 4, 5, 6, 7);
AddStudentCourses(students[568903], 1, 4);
AddStudentCourses(students[951357], 1, 5, 7);
AddStudentCourses(students[741369], 0, 2, 3, 6, 7);
AddStudentCourses(students[852146], 0, 1, 2, 3, 4, 5, 6);
}
测试:
var admin = new Admin();
admin.EnrollStudents();
var orderedStudents = admin.students.Values
.OrderBy(s => s.LastName)
.ThenBy(s => s.FirstName);
foreach (var student in orderedStudents) {
Console.WriteLine($"{student.LastName} {student.FirstName} ({student.EnrollmentId})");
IOrderedEnumerable<Course> orderedCourses = student.Courses.OrderBy(c => c.CourseName);
foreach (var course in orderedCourses) {
Console.WriteLine($" {course.CourseName} ({course.CourseID})");
}
Console.WriteLine();
}
打印
Bailey Majea (852146)
Accounts (101)
Bio_Psychology (102)
Business (103)
Chemistry (104)
Computer Science/Web Design/Cybersecurity Accounts (105)
Psychology (106)
Statistics (107)
Bailey Myrai (741369)
Accounts (101)
Advance Math (108)
Business (103)
Chemistry (104)
Statistics (107)
Beckam Olivia (951357)
Advance Math (108)
Bio_Psychology (102)
Psychology (106)
Jones Tom (111111)
Accounts (101)
Business (103)
Computer Science/Web Design/Cybersecurity Accounts (105)
Riley Jake (568903)
Bio_Psychology (102)
Computer Science/Web Design/Cybersecurity Accounts (105)
Thomas Mark (101203)
Advance Math (108)
Bio_Psychology (102)
Computer Science/Web Design/Cybersecurity Accounts (105)
Psychology (106)
Statistics (107)