How create a new deep copy clone of a List T

Question

In the following piece of code    using System  using System Collections Generic  using System Drawing  using System Windows Forms   namespace clone test 01        public partial class MainForm   Form                public class Book                       public string title                    public Book string title                                this title   title                                    public MainForm                         InitializeComponent                 List lt Book gt  books 1   new List lt Book gt                 books 1 Add   new Book  One                   books 1 Add   new Book  Two                   books 1 Add   new Book  Three                   books 1 Add   new Book  Four                    List lt Book gt  books 2   new List lt Book gt  books 1                books 2 0  title    Five               books 2 1  title    Six                textBox1 Text   books 1 0  title              textBox2 Text   books 1 1  title                       I use a Book object type to create a List lt T gt  and I populate it with a few items giving them a unique title  from  one  to  five     Then I create List lt Book gt  books 2   new List lt Book gt  books 1     From this point  I know it s a clone of the list object  BUT the book objects from book 2 are still a reference from the book objects in books 1  It s proven by making changes on the two first elements of books 2  and then checking those same elements of book 1 in a TextBox   books 1 0  title and books 2 1  title have indeed been changed to the new values of books 2 0  title and books 2 1  title   NOW THE QUESTION  How do we create a new hard copy of a List lt T gt   The idea is that books 1 and books 2 become completely independent of each other   I m disappointed Microsoft didn t offer a neat  fast and easy solution like Ruby are doing with the clone   method   What would be really awesome from helpers is to use my code and alter it with a workable solution so it can be compiled and work  I think it will truly help newbies trying to understand offered solutions for this issue   EDIT  Note that the Book class could be more complex and have more properties  I tried to keep things simple

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List lt Book gt  books 2   new List lt Book gt  books 2 ToArray       That should do exactly what you want  Demonstrated here

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You can use this   var newList  JsonConvert DeserializeObject lt List lt Book gt  gt  list toJson

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Well   If you mark all involved classes as serializable you can    public static List lt T gt  CloneList lt T gt  List lt T gt  oldList        BinaryFormatter formatter   new BinaryFormatter      MemoryStream stream   new MemoryStream      formatter Serialize stream  oldList     stream Position   0    return  List lt T gt  formatter Deserialize stream              Source    https   social msdn microsoft com Forums en-US 5c9b4c31-850d-41c4-8ea3-fae734b348c4 copy-listsomeobject-to-clone-list forum csharpgeneral

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Straight forward simple way to copy any generic list    List lt whatever gt  originalCopy new List lt whatever gt      create new list originalCopy AddRange original    perform copy of original list

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Create a generic ICloneable lt T gt  interface which you implement in your Book class so that the class knows how to create a copy of itself   public interface ICloneable lt T gt        T Clone       public class Book   ICloneable lt Book gt        public Book Clone                 return new Book      set properties                 You can then use either the linq or ConvertAll methods that Mark mentioned   List lt Book gt  books 2   books 1 Select book   gt  book Clone    ToList      or  List lt Book gt  books 2   books 1 ConvertAll book   gt  book Clone

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public static class Cloner       public static T Clone lt T gt  this T item                FieldInfo   fis   item GetType   GetFields BindingFlags Instance   BindingFlags Public   BindingFlags NonPublic           object tempMyClass   Activator CreateInstance item GetType             foreach  FieldInfo fi in fis                        if  fi FieldType Namespace    item GetType   Namespace                  fi SetValue tempMyClass  fi GetValue item                else                               object obj   fi GetValue item                   if  obj    null                      fi SetValue tempMyClass  obj Clone                                     return  T tempMyClass

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You need to create new Book objects then put those in a new List   List lt Book gt  books 2   books 1 Select book   gt  new Book book title   ToList      Update  Slightly simpler    List lt T gt  has a method called ConvertAll that returns a new list   List lt Book gt  books 2   books 1 ConvertAll book   gt  new Book book title

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If the Array class meets your needs  you could also use the List ToArray method  which copies elements to a new array    Reference  http   msdn microsoft com en-us library x303t819 v vs 110  aspx

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I m disappointed Microsoft didn t offer a neat  fast and easy solution like Ruby are doing with the clone   method    Except that does not create a deep copy  it creates a shallow copy   With deep copying  you have to be always careful  what exactly do you want to copy  Some examples of possible issues are    Cycle in the object graph  For example  Book has an Author and Author has a list of his Books  Reference to some external object  For example  an object could contain open Stream that writes to a file  Events  If an object contains an event  pretty much anyone could be subscribed to it  This can get especially problematic if the subscriber is something like a GUI Window    Now  there are basically two ways how to clone something    Implement a Clone   method in each class that you need cloned   There is also ICloneable interface  but you should not use that  using a custom ICloneable lt T gt  interface as Trevor suggested is okay   If you know that all you need is to create a shallow copy of each field of this class  you could use MemberwiseClone   to implement it  As an alternative  you could create a    copy constructor     public Book Book original   Use serialization to serialize your objects into a MemoryStream and then deserialize them back  This requires you to mark each class as  Serializable  and it can also be configured what exactly  and how  should be serialized  But this is more of a    quick and dirty    solution  and will most likely also be less performant

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Since Clone would return an object instance of Book  that object would first need to be cast to a Book before you can call ToList on it   The example above needs to be written as   List lt Book gt  books 2   books 1 Select book   gt   Book book Clone    ToList

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C  9 records and with expressions can make it a little easier  especially if your type has many properties  You can use something like  var books2   books1 Select b   gt  b with      ToList     I did this as an example  record Book       public string Name   get  set       static void Main         List lt Book gt  books1   new List lt Book gt                  new Book   Name    quot Book1 1 quot             new Book   Name    quot Book1 2 quot             new Book   Name    quot Book1 3 quot                var books2   books1 Select b   gt  b with      ToList         books2 0  Name    quot Changed quot       books2 1  Name    quot Changed quot        Console WriteLine  quot Book1 quot        foreach  var item in books1                Console WriteLine item              Console WriteLine  quot Book2 quot        foreach  var item in books2                Console WriteLine item            And the result was   Book1 Book   Name   Book1 1   Book   Name   Book1 2   Book   Name   Book1 3   Book2 Book   Name   Changed   Book   Name   Changed   Book   Name   Book1 3

[c#] How create a new deep copy (clone) of a List<T>?

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