How to initialize a list with constructor

Question

I have a type   public  class Human       public int Id   get  set        public string Address   get  set        public string Name   get  set        public List lt ContactNumber gt  ContactNumbers   get  set         public Human int id                Id   id             public Human int id  string address  string name                   List lt ContactNumber gt  contactNumbers            this id                Address   address          Name   name          ContactNumbers   contactNumbers                    Please guide me is among best practices to use constructor with for list initialization  How to initialize a list using constructor   Edit   Please guide me is among best practices to use constructor with for list initialization  How to assign values to list using a constructor  so if no value passed a default will be used   Thanks

User · Answer

You can initialize it just like any list:

public List<ContactNumber> ContactNumbers { get; set; }

public Human(int id)
{
    Id = id;
    ContactNumbers = new List<ContactNumber>();
}

public Human(int id, string address, string name) :this(id)
{
    Address = address;
    Name = name;
    // no need to initialize the list here since you're
    // already calling the single parameter constructor
}

However, I would even go a step further and make the setter private since you often don't need to set the list, but just access/modify its contents:

public List<ContactNumber> ContactNumbers { get; private set; }

User · Answer

Using a collection initializer  From C  3  you can use collection initializers to construct a List and populate it using a single expression  The following example constructs a Human and its ContactNumbers   var human   new Human 1   Address    Name         ContactNumbers   new List lt ContactNumber gt              new ContactNumber 1           new ContactNumber 2           new ContactNumber 3            Specializing the Human constructor  You can change the constructor of the Human class to provide a way to populate the ContactNumbers property   public class Human       public Human int id  string address  string name  IEnumerable lt ContactNumber gt  contactNumbers    this id  address  name                ContactNumbers   new List lt ContactNumber gt  contactNumbers              public Human int id  string address  string name  params ContactNumber   contactNumbers    this id  address  name                ContactNumbers   new List lt ContactNumber gt  contactNumbers               Using the first constructor  List lt ContactNumber gt  numbers   List lt ContactNumber gt          new ContactNumber 1       new ContactNumber 2       new ContactNumber 3      var human   new Human 1   Address    Name   numbers       Using the second constructor  var human   new Human 1   Address    Name       new ContactNumber 1       new ContactNumber 2       new ContactNumber 3       Bottom line  Which alternative is a best practice  Or at least a good practice  You judge it  IMO  the best practice is to write the program as clearly as possible to anyone who has to read it  Using the collection initializer is a winner for me  in this case  With much less code  it can do almost the same things as the alternatives -- at least  the alternatives I gave

User · Answer

Are you looking for this   ContactNumbers   new List lt ContactNumber gt     new ContactNumber  555-5555                                                new ContactNumber  555-1234                                                new ContactNumber  555-5678

User · Answer

In general don t expose List lt T gt  publicly  and don t provide setters for collection properties  Also  you may want to copy the elements of the passed list  as shown below   Otherwise changes to the original list will affect the Human instance   public class Human       public Human                    public Human IEnumerable lt ContactNumber gt  contactNumbers                if  contactNumbers    null                        throw new ArgumentNullException  contactNumbers                        contactNumbers AddRange contactNumbers              public IEnumerable lt ContactNumber gt  ContactNumbers               get   return  contactNumbers               private readonly List lt ContactNumber gt   contactNumbers   new List lt ContactNumber gt         Another option is to use the list constructor that takes a collection and remove the field initializer

User · Answer

ContactNumbers   new List lt ContactNumber gt       If you want it to be passed in  just take  public Human List lt ContactNumber gt  numbers     ContactNumbers   numbers

[c#] How to initialize a list with constructor?

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