Question

我建了一本字典：

Dictionary<int, Student> students = new Dictionary<int, Student>();

以下课程：

public class Student
    {
        public int StudentId { get; set; }
        public string Name { get; set; }
        public List<Course> Courses { get; set; }
    }

StudentId是关键。现在我想迭代字典并打印每个StudentId和学生姓名，以及每个学生注册的课程列表。我知道如何迭代字典：

foreach (KeyValuePair<int, Student> student in students)
        {
            resultLabel.Text = String.Format("<br />Student ID: {0}  Student Name: {1} ", student.Key, ???);

但我不知道如何1）打印出学生和2）迭代并打印每个学生的课程列表。任何帮助将不胜感激。

Answer 1

正如您对问题的评论中所建议的那样，更好地理解KeyValue对和迭代器可能是有益的。尽管如此，当您在上面显示嵌套结构并希望将其打印在一行时，String.Join函数会派上用场。

foreach (KeyValuePair<int, Student> student in students)
{
     var courses = String.Join(", ", student.Value.Courses);
     var output = String.Format("ID: {0}, Name: {1}, Courses: {2}", student.Key, student.Value.Name, courses);

    // Alternatively you could iterate over the courses here
    // foreach (Course course in student.Value.Courses) ...

     resultLabel.Text = String.Concat("<br />", output);
}

Answer 2

尝试这样的事情

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {

            List<Student> students = new List<Student>() {
                   new Student(new List<int>() {100,103,106}) { StudentId = 1001, Name = "John"}, 
                   new Student(new List<int>() {101,104,105}) { StudentId = 1002, Name = "Mary"},
                   new Student(new List<int>() {102,105,104}) { StudentId = 1003, Name = "Tom"},
                   new Student(new List<int>() {103,106,102}) { StudentId = 1004, Name = "Dick"},
                   new Student(new List<int>() {104,101,102}) { StudentId = 1005, Name = "Harry"}
                };

            Dictionary<int, Student> dictStudents = students.AsEnumerable()
                .GroupBy(x => x.StudentId, y => y)
                .ToDictionary(x => x.Key, y => y.FirstOrDefault());

            foreach (KeyValuePair<int, Student> student in dictStudents)
            {
                string message = String.Format("<br />Student ID: {0}  Student Name: {1} Courses: {2}", 
                    student.Key.ToString(),
                    student.Value.Name,
                    string.Join(",", student.Value.Courses.Select(x => "CourseID=" + x.CourseID.ToString() + ":" + "Course Name= " + x.Name).ToArray()));
                Console.WriteLine(message);
            }
            Console.ReadLine();

        }
    }
    public class Student
    {
        public int StudentId { get; set; }
        public string Name { get; set; }
        public List<Course> Courses { get; set; }

        public Student() { Courses = new List<Course>();}
        public Student(List<int> couseNumbers)
        {
            Courses = new List<Course>();
            foreach(int id in couseNumbers)
            {
                Courses.Add(Course.courses.Where(x => x.CourseID == id).FirstOrDefault()); 
            }
        }
    }
    public class Course
    {
        public static List<Course> courses = new List<Course>() {
                new Course() {CourseID = 100, Name = "abc"},
                new Course() {CourseID = 101, Name = "abd"},
                new Course() {CourseID = 102, Name = "abe"},
                new Course() {CourseID = 103, Name = "abf"},
                new Course() {CourseID = 104, Name = "abg"},
                new Course() {CourseID = 105, Name = "abh"},
                new Course() {CourseID = 106, Name = "abi"}
        };

        public int CourseID { get; set; }
        public string Name { get; set; }
    }
}

当其中一个属性是列表时，如何迭代字典

2 个答案: