Contains on a list of custom class objects

Question

I m trying to use the  Contains   function on a list of custom objects  This is the list   List lt CartProduct gt  CartProducts   new List lt CartProduct gt       And the CartProduct   public class CartProduct       public Int32 ID      public String Name      public Int32 Number      public Decimal CurrentPrice           lt summary gt                    lt  summary gt           lt param name  ID  gt The ID of the product lt  param gt           lt param name  Name  gt The name of the product lt  param gt           lt param name  Number  gt The total number of that product lt  param gt           lt param name  CurrentPrice  gt The currentprice for the product  1 piece  lt  param gt      public CartProduct Int32 ID  String Name  Int32 Number  Decimal CurrentPrice                this ID   ID          this Name   Name          this Number   Number          this CurrentPrice   CurrentPrice            public String ToString                 return Name            So i try to find a similar cartproduct within the list   if  CartProducts Contains p     But it ignores similar cartproducts and i don t seem to know what it checks on - the ID  or it all   Thanks in advance

User · Answer

By default reference types have reference equality (i.e. two instances are only equal if they are the same object).

You need to override Object.Equals (and Object.GetHashCode to match) to implement your own equality. (And it is then good practice to implement an equality, ==, operator.)

User · Answer

You need to create a object from your list like    List lt CartProduct gt  lst   new List lt CartProduct gt      CartProduct obj   lst Find x   gt   x Name     product name       That object get the looked value searching by their properties  x name  Then you can use List methods like Contains or Remove   if  lst Contains obj        lst Remove obj

User · Answer

If you are using  NET 3 5 or newer you can use LINQ extension methods to achieve a  contains  check with the Any extension method   if CartProducts Any prod   gt  prod ID    p ID     This will check for the existence of a product within CartProducts which has an ID matching the ID of p  You can put any boolean expression after the   gt  to perform the check on   This also has the benefit of working for LINQ-to-SQL queries as well as in-memory queries  where Contains doesn t

User · Answer

Implement override Equals   and GetHashCode    public class CartProduct       public Int32 ID               public CartProduct Int32 ID                     this ID   ID                         public override int GetHashCode                 return ID             public override bool Equals Object obj                        if  obj    null      obj is CartProduct                   return false              else                 return GetHashCode        CartProduct obj  GetHashCode                   used   if  CartProducts Contains p

User · Answer

You need to implement IEquatable or override Equals   and GetHashCode    For example   public class CartProduct   IEquatable lt CartProduct gt        public Int32 ID      public String Name      public Int32 Number      public Decimal CurrentPrice       public CartProduct Int32 ID  String Name  Int32 Number  Decimal CurrentPrice                this ID   ID          this Name   Name          this Number   Number          this CurrentPrice   CurrentPrice             public String ToString                 return Name             public bool Equals  CartProduct other                    Would still want to check for null etc  first          return this ID    other ID  amp  amp                  this Name    other Name  amp  amp                  this Number    other Number  amp  amp                  this CurrentPrice    other CurrentPrice

User · Answer

It checks to see whether the specific object is contained in the list   You might be better using the Find method on the list   Here s an example  List lt CartProduct gt  lst   new List lt CartProduct gt      CartProduct objBeer  objBeer   lst Find x   gt   x Name     Beer       Hope that helps  You should also look at LinQ - overkill for this perhaps  but a useful tool nonetheless

User · Answer

If you want to have control over this you need to implement the  IEquatable interface  1    1   http   This method determines equality by using the default equality comparer  as defined by the object s implementation of the IEquatable Equals method for T  the type of values in the list

[c#] .Contains() on a list of custom class objects

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