We Keep Coding

put the value inside the array inside a class

I have a following class:
public class test100
{
public string dateofbirth{ get; set; }
public string phonenumber{ get; set; }
public Name[] names { get; set; }
}
I want to assign value to names and then add that value in test100 class. I don't want to create the list. I just want to do this with an array. I want to put the values like this:
names[0] = {firstName="test1", MiddleName="test2", lastName="test3"}
and then add names[0] to test100 class.
How can I achieve this.

You can initialize the array while initializing the class itself
var data = new test100
{
dateofbirth = "22-03-1997",
phonenumber = "1-223344",
names = new Name[]
{
new Name {firstName="test1", MiddleName="test2", lastName="test3"}
}
}
Problem with this is that you haven't defined any size for your names array. So you can create instance of your class, define the size of that array and then insert the object to that array
var data = new test100();
data.names = new Name[10];
Name name = new Name {firstName="test1", MiddleName="test2", lastName="test3"};
data.names[0] = name;

Is it normal to have a list of objects in an object?

I'm new to OO design, and I wondering whether it is typical to have designs where objects contain lists of other objects. An example is below:
// Person object containing a list of phone numbers
public class Person
{
public Guid Id { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
public List<Phone> Contacts { get; set; }
public void AddPhoneNumber(Phone phone)
{
Contacts.Add(phoneNumber);
}
}
// Phone object
public class Phone
{
public Guid Id { get; set; }
public string Name { get; set; }
public string Number { get; set; }
}
// Example code to establish an object:
Person p1 = new Person();
p1.FirstName = "John";
p1.LastName = "Smith";
p1.AddPhoneNumber(new Phone() { Number = "555957000" });
p1.AddPhoneNumber(new Phone() { Number = "555579561" });
Is there a better way to structure this that simplifies the design and allows easier access to the data? Thanks!

Yes, it is absolutely fine to have an object contains list of object. In OOPs this is called Composition, which represent strong relationship between participating class.

I wondering whether it is typical to have designs where objects
contain lists of other objects.
Absolutely, this is normal as an object can contain lists that belong to only that particular object. One of many examples is when you're traversing a binary tree or such you could have each node have their own list which identifies their children. There are many more cases in which an object should/could contain their own list.
Going back to your code, you seem to have an error because the code below states that the list will contain Phone objects.
public List<Phone> Contacts { get; set; }
but yet you're passing in a string object rather than a phone object.
public void AddPhoneNumber(string phoneNumber)
{
Contacts.Add(phoneNumber); // this code shouldnt compile
}
rather what you can do is this:
public void AddPhoneNumber(string phoneNumber)
{
Contacts.Add(new Phone() { Number = phoneNumber });
}

There's nothing wrong with your code. It's perfectly valid to have a list of objects within an object.
Though adding a string to your List of Phone objects will throw an error.
You can add a phone number like so:
Person p1 = new Person();
p1.Contacts.Add(new Phone() { Number = "555579561" });

Using Array of Arrays for One to Many Relationship in C#

I am making a console test with C#.
Actually I have never used of C# but VB.Net. I want to create arrays for one-to-many relationship.
My one is 'A Student' has 'Name','Sex',...,'Courses Taken'.
A Student would take many course, each course has a Title and Included Subject. Each subject has Name, Description and Point.
Like this.
Student
- Name - Sex - Courses Taken
Take Courses
- Course Title - Subject Included
Subject
- Subject Name [Math] [MVC]
- Subject description [Advance] [Building Website]
- Subject Point [6.9] [5.6]
I want to store each entity in Arrays but I don't know how to connect subjects/courses to each Students. And how can I get Student who attending Math or MVC. Because every students can have more then more course/ more than one subjects.

You'll want to create classes to describe your different objects.
class Student
{
string Name { get; set; }
Gender Sex { get; set; } // write an enum for this
IEnumerable<Course> CoursesTaken { get; set; }
}
class Course
{
string Title { get; set; }
Subject Subject { get; set; }
}
class Subject
{
string Name { get; set; }
string Description { get; set; }
double Points { get; set; }
}
Using List to create enumerations of instances of these new types allow you to use LINQ to select or evaluate members of the list (nested for loops work as well):
// populate a list of students called studentList
//...
// use LINQ to select the students you want
var mathResults = studentList.Where(student => student.CoursesTaken.Any(course => course.Subject.Name == "Math"));

I feel like I've done with it in good way...
Pls check my code for my ques! ^^
I first made 3 classes as below..
class Students
{
public string StudentName;
public int StudSize;
public bool StudSex;
public List<Take_Courses> tcourses;
public Students() { }
public Students(string name, int size, bool sex, List<Take_Courses> tcourses)
{
StudentName = name;
StudSize = size;
StudSex = sex;
this.tcourses = tcourses;
}
}
and
class Take_Courses
{
public string classname;
public List<Arr_Courses> arr_Course;
public Take_Courses() { }
public Take_Courses(string classname, List<Arr_Courses> arr_courses)
{
this.classname = classname;
arr_Course = arr_courses;
}
}
class Arr_Courses
{
public string cosname;
public string cosdesc;
public float cospoint;
public Arr_Courses() { }
public Arr_Courses(string name, string description, float point)
{
cosname = name;
cosdesc = description;
cospoint = point;
}
}
I then initialized values in Main class as below;
Arr_Courses acos=new Arr_Courses();
Arr_Courses acos1=new Arr_Courses("Math","Advance Math1",9.5f);
Take_Courses cos=new Take_Courses();
Take_Courses cos_take1=new Take_Courses("Info Tech",new List<Arr_Courses>{acos1});
Students stu=new Students();
Students Stu1 = new Students("Milla", 22, true,new List<Take_Courses>{cos_take1});
I then make another List to be generated names of student and use for looping and assign each one to List.
I think some important part is this.
if (arr_stud[i].tcourses[j].arr_Course[k].cosname.Equals("Math"))
{
Math_Stud++;
MathStudents[i] = arr_stud[i];
}
I am sharing this if anyone needs something like this. Any ungraded codes is appreciated to be shared. Thanks so so.

"Object reference not set to an instance of an object" error when trying to add objects to a list inside a class [duplicate]

This question already has answers here:
What is a NullReferenceException, and how do I fix it?
(27 answers)
Closed 8 years ago.
I have some custom classes defined that include lists of other classes like so:
public class Unit
{
public string Name { get; set; }
public List<Group> Contains { get; set; }
}
public class Group
{
public string Name { get; set; }
public Type Type { get; set; }
public int Number { get; set; }
}
public static Type basic_1 = new Type() { Name = "basic_1", Number = 1, Cost = 13 };
The basic idea is that you have a unit which contains a list of groups, each with a different type. The type contains specific properties while the classes that contain them are organizational in nature.
I then try to start building out these classes like so:
Unit unit1 = new Unit() { Name = "Unit 1" };
Group group1 = new Group() { Name = "Group 1", Number = 10, Type = basic_1 };
unit1.Contains.Add(group1);
But here I receive the error (on the Add method) "Object reference not set to an instance of an object." Looking at the locals in the debugger I can see that the Unit, Group and Type were all created successfully and the group1 contains all the Type values it's supposed to, but unit1.Contains is null.
What am I doing wrong? FYI I've never done something like this before so I don't even know if it's possible, but it seems to work fine up until this point.

Your List<Group> Contains never gets initialized, so when you try to access it, you get a null reference exception. Essentially all null reference exceptions are the same, you're trying to use an object that's null.
In this case, let's just add a default constructor to initialize the list for us.
public class Unit
{
public string Name { get; set; }
public List<Group> Contains { get; set; }
public Unit()
{
Contains = new List<Group>();
}
}
By the way, Contains is a terrible name for a list. Contains is usually a function call, as it's a verb. Usually better to use a noun for a collection, such as Groups.
public class Unit
{
public string Name { get; set; }
public List<Group> Groups { get; set; }
public Unit()
{
Groups = new List<Group>();
}
}

Your Contains list within User class never gets instantiated.
You may want to change your User class to this instead:
public class Unit
{
public string Name { get; set; }
List<Group> list = new List<Group>();
public List<Group> Contains
{
get { return list; }
}
}
As you can see the Contains property now only returns a list instance that can of course be modified but never reaffected. Likely, this is what you'll want.
Although this is a tad outside the scope of your question, I would suggest that you rename the Contains property to Groups instead.

You have initialized the Unit But Unit.Contains Does not initialize. Before Adding objects to Contains list it must be initialized.
Unit unit1 = new Unit() { Name = "Unit 1" };
Group group1 = new Group() { Name = "Group 1", Number = 10, Type = basic_1 };
unit1.Contains = new List<Group>();
unit1.Contains.Add(group1);
Or
In your Unit class constructor you can initialize List here the code
public class Unit
{
public string Name { get; set; }
public List<Group> Contains { get; set; }
public Unit()
{
Contains = new List<Group>();
}
}
I would prefer the 2nd solution as it will make sure that whenever Unit is initialized Contains will be initialized automatically.

VS 2010 Report Viewer Cannot Access Nested Collections, Anyone?

I have gone through all the walk through on MSDN as usual they are worthless - extremely limited.
If I make the internal object in my class a single class I can display the information, but as soon as I convert it to a list of objects ( a collection ) I get the #Error in the display.
Here is an updated example.
For an example I have a Person object that can have one or more phone numbers ( list of numbers ) and I cannot find a way to access the phone numbers.
[Serializable]
public class Person
{
private readonly List<PhoneNumber> _numbers = new List<PhoneNumber>();
public Person()
{
}
public Person(int id, string name, string address, decimal salary)
{
Id = id;
Name = name;
Address = address;
Salary = salary;
}
public void AddNumber(PhoneNumber number)
{
_numbers.Add(number);
}
public int Id { get; set; }
public string Name { get; set; }
public string Address { get; set; }
public List<PhoneNumber> PhoneNumbers { get { return _numbers; } }
}
[Serializable]
public class PhoneNumber
{
public PhoneNumber()
{
}
public PhoneNumber(int id, string areaCode, string phone)
{
AreaCode = areaCode;
Id = id;
Phone = phone;
}
public string AreaCode { get; set; }
public string Phone { get; set; }
public int Id { get; set; }
}
I then populate the collections.
var persons = new List<Person>();
var t = new Person(1, "Mike", "5150 Nuts", 125);
t.AddNumber(new PhoneNumber(1, "425", "455"));
t.AddNumber(new PhoneNumber(1, "425", "450"));
persons.Add(t);
t = new Person(2, "Tom", "1055 MS HAS NO DOCUMENTATION AS USUAL!", 1245);
t.AddNumber(new PhoneNumber(2, "TYPICAL", "OF-THEM"));
t.AddNumber(new PhoneNumber(2, "ANY", "ONE???"));
persons.Add(t);
I then assign everything to the report.
reportViewer1.ProcessingMode = ProcessingMode.Local;
reportViewer1.LocalReport.ReportPath = "..\\..\\Report1.rdlc";
reportViewer1.LocalReport.DataSources.Add(new ReportDataSource("Person",persons));
reportViewer1.RefreshReport();
In the report it displays the people will display without issue as I add the text boxes to a list and then group the list by Id. When I try to display the phone numbers, I get the #ERROR message, and for the life of me I cannot seem to find a way to display the list of numbers that are assigned to a person.
If I change the object from List<PhoneNumber> within the person class to PhoneNumber I can access it, but when trying to display a List<PhoneNumber> I cant.
I need to be ale to display List<of objects> within an Class Item.

The nested collection must be displayed as a subreport where the nested collection is an separate data source. You must bind the event LocalReport.SubreportProcessing to a handler that will filter and bind the datasource (PhoneNumbers) to the subreport as a seperate report data source. The example at the link provided should get you where you need to go.