初始化對象後的方法nullreference

Question

我在C＃中相對較新，我只是想在語言中使用它。

我有三個班，即學生，課程和成績。我似乎無法理解爲什麼它始終得到一個空值。

class Student 
{ 
    Name name; 
    Course course; 

    public Student(Course course) 
    { 
     this.course = course; 
    } 

    public Course C 
    { 
     get { return course; } 
     set { course = value; } 
    } 

} 

class Course 
{ 
    string name; 
    string code; 
    int units; 
    Grade grade; // this one warns as 'Course.grade' is never assigned to, and will always have its default value null 

    public Course(string name, string code) 
    { 
     this.name = name; 
     this.code = code; 
    } 

    public void DisplayDetails() 
    { 
     Console.WriteLine("Course: {0}({1})", code, name); 
    } 

    public int U 
    { 
     get { return units; } 
     set { units = value; } 
    } 

    public Grade G 
    { 
     get { return grade; } 
     set { value = grade; } 
    } 
} 

class Grade 
{ 
    double q; 
    double o; 
    double fe; 
    double fg; 

    public Grade(double q, double o, double fe) 
    { 
     this.q = q; 
     this.o = o; 
     this.fe = fe; 
    } 

    public void ComputeGrade() 
    { 
     fg = q * .5 + o * .2 + fe * .3; 
    } 

    public double C 
    { 
     get { return fg; } 
     set { value = fg; } 
    } 

} 

這是我的主要課程。

class Program 
{ 
    static void Main(string[] args) 
    { 
     Student s = new Student(new Course("Something", "1234")); 
     s.C.U = 3; 
     s.N = new Name("John", "Snow"); 
     Grade grade = new Grade(90.0, 90.0, 90.0); // I have initialized an object here 


     s.C.G.ComputeGrade(); //but this gets a null value 

     s.N.Display2(); 
     s.C.DisplayDetails(); 
     Console.WriteLine(" - {0} units", s.C.U); 
     Console.WriteLine(" Grade: {0}", s.C.G.C); //as well as this 
     Console.ReadKey(); 

    } 
} 

我相信已經設置了Grade對象的值。我也宣佈它是getter/setter。我是在做錯代碼還是缺少代碼？

Answer 1

正確G設定器在Course類：

public Grade G 
{ 
    get { return grade; } 
    set { grade = value; } 
} 

和使用等的Fabio之前設置G值表明：

s.C.G = new Grade(90.0, 90.0, 90.0);