Does List T guarantee insertion order

Question

Say I have 3 strings in a List  e g   quot 1 quot   quot 2 quot   quot 3 quot    Then I want to reorder them to place  quot 2 quot  in position 1  e g   quot 2 quot   quot 1 quot   quot 3 quot    I am using this code  setting indexToMoveTo to 1   listInstance Remove itemToMove   listInstance Insert indexToMoveTo  itemToMove    This seems to work  but I am occasionally getting strange results  sometimes the order is incorrect or items from the list are getting deleted  Any ideas  Does List lt T gt  guarantee order  Related   Does a List lt T gt  guarantee that items will be returned in the order they were added

User · Answer

If you will change the order of operations  you will avoid the strange behavior  First insert the value to the right place in the list  and then delete it from his first position  Make sure you delete it by his index  because if you will delete it by reference  you might delete them both

User · Answer

As Bevan said  but keep in mind  that the list-index is 0-based  If you want to move an element to the front of the list  you have to insert it at index 0  not 1 as shown in your example

User · Answer

The List lt  gt  class does guarantee ordering - things will be retained in the list in the order you add them  including duplicates  unless you explicitly sort the list   According to MSDN         List  Represents a strongly typed list of objects that can be   accessed by index     The index values must remain reliable for this to be accurate  Therefore the order is guaranteed   You might be getting odd results from your code if you re moving the item later in the list  as your Remove   will move all of the other items down one place before the call to Insert     Can you boil your code down to something small enough to post

User · Answer

Here are 4 items  with their index  0  1  2  3 K  C  A  E   You want to move K to between A and E -- you might think position 3  You have be careful about your indexing here  because after the remove  all the indexes get updated   So you remove item 0 first  leaving  0  1  2 C  A  E   Then you insert at 3  0  1  2  3 C  A  E  K   To get the correct result  you should have used index 2  To make things consistent  you will need to send to  indexToMoveTo-1  if indexToMoveTo  gt  indexToMove  e g   bool moveUp    listInstance IndexOf itemToMoveTo   gt  indexToMove   listInstance Remove itemToMove   listInstance Insert indexToMoveTo  moveUp    itemToMoveTo - 1    itemToMoveTo     This may be related to your problem  Note my code is untested   EDIT  Alternatively  you could Sort with a custom comparer  IComparer  if that s applicable to your situation

User · Answer

This is the code I have for moving an item down one place in a list   if  this folderImages SelectedIndex  gt  -1  amp  amp  this folderImages SelectedIndex  lt  this folderImages Items Count - 1        string imageName   this folderImages SelectedItem as string      int index   this folderImages SelectedIndex       this folderImages Items RemoveAt index       this folderImages Items Insert index   1  imageName       this folderImages SelectedIndex   index   1       and this for moving it one place up   if  this folderImages SelectedIndex  gt  0        string imageName   this folderImages SelectedItem as string      int index   this folderImages SelectedIndex       this folderImages Items RemoveAt index       this folderImages Items Insert index - 1  imageName       this folderImages SelectedIndex   index - 1      folderImages is a ListBox of course so the list is a ListBox ObjectCollection  not a List lt T gt   but it does inherit from IList so it should behave the same  Does this help   Of course the former only works if the selected item is not the last item in the list and the latter if the selected item is not the first item

[c#] Does List<T> guarantee insertion order?

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