What is the use of ObservableCollection in net

Question

What is the use of ObservableCollection  in  net

User · Answer

it is a collection which is used to notify mostly UI to change in the collection , it supports automatic notification.

Mainly used in WPF ,

Where say suppose you have UI with a list box and add button and when you click on he button an object of type suppose person will be added to the obseravablecollection and you bind this collection to the ItemSource of Listbox , so as soon as you added a new item in the collection , Listbox will update itself and add one more item in it.

User · Answer

From Pro C  5 0 and the  NET 4 5 Framework  The ObservableCollection lt T gt  class is very useful in that it has the ability to inform external objects when its contents have changed in some way  as you might guess  working with ReadOnlyObservableCollection lt T gt  is very similar  but read-only in nature   In many ways  working with the ObservableCollection lt T gt  is identical to working with List lt T gt   given that both of these classes implement the same core interfaces  What makes the ObservableCollection lt T gt  class unique is that this class supports an event named CollectionChanged  This event will fire whenever a new item is inserted  a current item is removed  or relocated   or if the entire collection is modified  Like any event  CollectionChanged is defined in terms of a delegate  which in this case is NotifyCollectionChangedEventHandler  This delegate can call any method that takes an object as the first parameter  and a NotifyCollectionChangedEventArgs as the second  Consider the following Main   method  which populates an observable collection containing Person objects and wires up the CollectionChanged event   class Program      static void Main string   args               Make a collection to observe and add a few Person objects       ObservableCollection lt Person gt  people   new ObservableCollection lt Person gt                   new Person  FirstName    Peter   LastName    Murphy   Age   52            new Person  FirstName    Kevin   LastName    Key   Age   48                    Wire up the CollectionChanged event       people CollectionChanged    people CollectionChanged          Now add a new item       people Add new Person  Fred    Smith   32             Remove an item       people RemoveAt 0         Console ReadLine            static void people CollectionChanged object sender  System Collections Specialized NotifyCollectionChangedEventArgs e                 What was the action that caused the event          Console WriteLine  Action for this event   0    e Action               They removed something           if  e Action    System Collections Specialized NotifyCollectionChangedAction Remove                        Console WriteLine  Here are the OLD items                 foreach  Person p in e OldItems                                Console WriteLine p ToString                               Console WriteLine                          They added something           if  e Action    System Collections Specialized NotifyCollectionChangedAction Add                           Now show the NEW items that were inserted              Console WriteLine  Here are the NEW items                 foreach  Person p in e NewItems                                Console WriteLine p ToString                                      The incoming NotifyCollectionChangedEventArgs parameter defines two important properties  OldItems and NewItems  which will give you a list of items that were currently in the collection before the event fired  and the new items that were involved in the change  However  you will want to examine these lists only under the correct circumstances  Recall that the CollectionChanged event can fire when items are added  removed  relocated  or reset  To discover which of these actions triggered the event  you can use the Action property of NotifyCollectionChangedEventArgs  The Action property can be tested against any of the following members of the NotifyCollectionChangedAction enumeration   public enum NotifyCollectionChangedAction   Add   0  Remove   1  Replace   2  Move   3  Reset   4

User · Answer

ObservableCollection Caveat Mentioned above  Said Roohullah Allem   What makes the ObservableCollection class unique is that this class supports an event named CollectionChanged   Keep this in mind   If you adding a large number of items to an ObservableCollection the UI will also update that many times  This can really gum up or freeze your UI  A work around would be to create a new list  add all the items then set your property to the new list  This hits the UI once  Again   this is for adding a large number of items

User · Answer

ObservableCollection is a collection that allows code outside the collection be aware of when changes to the collection  add  move  remove  occur   It is used heavily in WPF and Silverlight but its use is not limited to there   Code can add event handlers to see when the collection has changed and then react through the event handler to do some additional processing   This may be changing a UI or performing some other operation   The code below doesn t really do anything but demonstrates how you d attach a handler in a class and then use the event args to react in some way to the changes   WPF already has many operations like refreshing the UI built in so you get them for free when using ObservableCollections  class Handler       private ObservableCollection lt string gt  collection       public Handler                 collection   new ObservableCollection lt string gt             collection CollectionChanged    HandleChange             private void HandleChange object sender  NotifyCollectionChangedEventArgs e                foreach  var x in e NewItems                           do something                    foreach  var y in e OldItems                          do something                   if  e Action    NotifyCollectionChangedAction Move                          do something

User · Answer

One of the biggest uses is that you can bind UI components to one  and they ll respond appropriately if the collection s contents change   For example  if you bind a ListView s ItemsSource to one  the ListView s contents will automatically update if you modify the collection   EDIT  Here s some sample code from MSDN  http   msdn microsoft com en-us library ms748365 aspx  In C   hooking the ListBox to the collection could be as easy as  listBox ItemsSource   NameListData    though if you haven t hooked the list up as a static resource and defined NameItemTemplate you may want to override PersonName s ToString     For example   public override ToString         return string Format   0   1    this FirstName  this LastName

User · Answer

An ObservableCollection works essentially like a regular collection except that it implements  the interfaces    INotifyCollectionChanged   INotifyPropertyChanged    As such it is very useful when you want to know when the collection has changed  An event is triggered that will tell the user what entries have been added removed or moved   More importantly they are very useful when using databinding on a form

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Explanation without Code For those wanting an answer without any code behind it  boom-tish  with a story  to help you remember   Normal Collections - No Notifications Every now and then I go to NYC and my wife asks me to buy stuff  So I take a shopping list with me  The list has a lot of things on there like   Louis Vuitton handbag   5000  Clive Christian   s Imperial Majesty Perfume   215 000   Gucci Sunglasses   2000   hahaha well I quot m not buying that stuff  So I cross them off and remove them from the list and I add instead   12 dozen Titleist golf balls  12 lb bowling ball   So I usually come home without the goods and she s never pleased  The thing is that she doesn t know about what i take off the list and what I add onto it  she  gets no notifications  The ObservableCollection - notifications when changes made Now  whenever I remove something from the list  she get s a notification on her phone  i e  sms   email etc   The observable collection works just the same way  If you add or remove something to or from it  someone is notified  And when they are notified  well then they call you and you ll get a ear-full  Of course the consequences are customisable via the event handler  That sums it all up

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class FooObservableCollection   ObservableCollection lt Foo gt        protected override void InsertItem int index  Foo item                base Add index  Foo            if  this CollectionChanged    null              this CollectionChanged this  new NotifyCollectionChangedEventArgs  NotifyCollectionChangedAction Add  item  index            var collection   new FooObservableCollection    collection CollectionChanged    CollectionChanged   collection Add new Foo      void CollectionChanged  object sender  NotifyCollectionChangedEventArgs e        Foo newItem   e NewItems OfType lt Foo gt    First

[c#] What is the use of ObservableCollection in .net?

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