Arraylist of structure problem

Arraylist of structure problem

• Kaos

  Consider using a class instead of a structure. Structures copy when boxed, and non-generics collections (System.Collections) uses object[] for internal storage (thus, boxing occurs).. consider the following:
  
  DataStruct d = new DataStruct(); // superfluous
  d.val = 1;
  myArrayList.Add(d);
  Console.WriteLine(Convert.ToString(((DataStruct)myArrayList[0]).val);
  ((DataStruct)myArrayList[0]).val = 2;
  Console.WriteLine(Convert.ToString(((DataStruct)myArrayList[0]).val);
  
  Output:
  1
  1
  
  Using a class will prevent the copying (structs are valuetype subclasses fwiw).
  
  Also, to avoid having to loop through a list to locate the entry you need to modify you can use a Hashtable instead:
  
  Hashtable h = new Hashtable();
  DataClass d = new DataClass();
  d.name = "foo";
  d.val = 1;
  h[d.name] = d;
  Console.WriteLine(Convert.ToString(((DataClass)h[0]).val);
  ((DataClass)h["foo"]).val = 2
  Console.WriteLine(Convert.ToString(((DataClass)h[0]).val);
  
  Output:
  1
  2
  
  If you're using .net 2.0 you should use a Dictionary<> (generics) instead of a Hashtable and a List<> instead of an ArrayList.
  
  Hope that helps, sorry for the C# it's what I'm used to.
  
  
  
  
  
  

• Deepak Rangarajan

  Thanks for your reply.
  I have a question though.
  In line:
  Console.WriteLine(Convert.ToString(((DataStruct)myArrayList[0]).val);
  Is 0 ihe arraylist index I can't really use it since I really don't know
  what index of the array to look for....

  An off topic question though, you said that I'd better use a class Right
  now I'm declaring the structure inside a class.Is it ok for me to declare a class
  inside another class

  Thanks for your time.

  
  

• Yeghia Dolbakyan

  Yes in my example [0] is just an index, i only used '0' for the example.
  
  Like i said, though, using a Dictionary/Hashtable would allow you to say ["Name"] instead of having to find the correct index at all.
  
  I'm a C# programmer and in C# there's no problems clearing classes within classes (inner types). I don't see why it wouldn't work in VB.NET, but seeing as I've never seen or tried it myself, I can't say for sure (wouldn't hurt to try it out though).
  
  
  
  
• Arraylist of structure problem