Person, Teacher , Student CRUD

[Algorithme T]

Hello,
I am trying to get a Person, Teacher,Student Crud done .
I initially worked with Person, Teacher,Student abstract classes (every thing was working perfectly well) then i decided to use those abstract classes as models and created 3 other classes which are Services such as PersonService , TeacherService ....

I am getting an error of "Unhandled exception. System.NullReferenceException: Object reference not set to an instance of an object." each time i am trying to use a method which are now found in the Services classes


<

PersonService? p = null;

            Person? pChange = null;

            switch (type)
            {
                case "student":
                    
                    if (lastName != null && id != null)
                    {
                        pChange = new Student(lastName, firstName, dateOfBirth, id);
                        try
                        {
                            p.Add(pChange);
                        }
                        catch(Exception ex)
                        {
                            Console.WriteLine("Success ");
                        }
                    }
                    break;
                case "teacher":
                    
                    int salary;
                    try
                    {
                         salary = Convert.ToInt32(Console.ReadLine());
                    }
                    catch (Exception ex)
                    {
                        
                        salary = 0;

                    }

                    if (lastName != null)
                    {
                        pChange = new Teacher(lastName, firstName, dateOfBirth, hireDate, salary);
                        p.Add(pChange);
                        
                    }

/>

 

[Skydiver]

On which line are you getting the exception?

 

[Algorithme T]

At

On which line are you getting the exception?

p.Add(pChange)

 

[Skydiver]

The error seems accurate. p was set to null on line 1. Perhaps p should be set to reference an instance of the PersonService.

 

[Algorithme T]

On which line are you getting the exception?

However reminding you that my class person contains just my attributes and my class PersonService has my methods ...
That is why I used p for PersonService and pChange for Person

 

[Skydiver]

See my post #4.

 

[Algorithme T]

The error seems accurate. p was set to null on line 1. Perhaps p should be set to reference an instance of the PersonService.

No doubt about that .. this time around I'm trying to figure out a way out

 

[Algorithme T]

See my post #4.

I'm new to the plateforme... Where can I see the post ?

 

[Skydiver]

Scroll up.

 

[Algorithme T]

This

The error seems accurate. p was set to null on line 1. Perhaps p should be set to reference an instance of the PersonService.

Post ? Oki .. thought of this earlier but how can I get this done is the real thing . Kind of new into C#

 

[Skydiver]

When you call new, you create a new instance of an object. Therefore:

p = new PersonService();
[/icode]

 

[Algorithme T]

When you call new, you create a new instance of an object. Therefore:

p = new PersonService();
[/icode]

I see .. same goes to Person ... Getting it done

 

[Algorithme T]

I replaced my

PersonService ? p = null!

To what you gave me but turns out not to work because my PersonService class is an abstract class

When you call new, you create a new instance of an object. Therefore:

p = new PersonService();
[/icode]

 

[Skydiver]

Then instantiate a concrete class seems to be the logical solution.