59

How can I do that? I need a list (of type ObservableCollection) where the latest item is first.

Gabe
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Jason94
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  • Do you need your collection to be observable otherwise a Stack is designed for this purpose. – Dave S Mar 27 '12 at 18:31

3 Answers3

125

Try using 

collection.Insert(0, item);

This would add item to the beginning of the collection (while Add adds to the end). More info here.

Dmitry Reznik
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  • using System.Linq; – 27k1 Jun 07 '18 at 16:47
  • this method is O(n), so it not recommended for large collections. https://learn.microsoft.com/en-us/dotnet/api/system.collections.objectmodel.collection-1.insert?redirectedfrom=MSDN&view=net-6.0#System_Collections_ObjectModel_Collection_1_Insert_System_Int32__0_ – Jawad Sabir Jan 27 '22 at 05:47
9

You should use a stack instead.

This is based on Observable Stack and Queue

Create an observable Stack, where stack is always last in first out (LIFO).

from Sascha Holl

public class ObservableStack<T> : Stack<T>, INotifyCollectionChanged, INotifyPropertyChanged
{
    public ObservableStack()
    {
    }

    public ObservableStack(IEnumerable<T> collection)
    {
        foreach (var item in collection)
            base.Push(item);
    }

    public ObservableStack(List<T> list)
    {
        foreach (var item in list)
            base.Push(item);
    }


    public new virtual void Clear()
    {
        base.Clear();
        this.OnCollectionChanged(new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Reset));
    }

    public new virtual T Pop()
    {
        var item = base.Pop();
        this.OnCollectionChanged(new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Remove, item));
        return item;
    }

    public new virtual void Push(T item)
    {
        base.Push(item);
        this.OnCollectionChanged(new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Add, item));
    }


    public virtual event NotifyCollectionChangedEventHandler CollectionChanged;


    protected virtual void OnCollectionChanged(NotifyCollectionChangedEventArgs e)
    {
        this.RaiseCollectionChanged(e);
    }

    protected virtual void OnPropertyChanged(PropertyChangedEventArgs e)
    {
        this.RaisePropertyChanged(e);
    }


    protected virtual event PropertyChangedEventHandler PropertyChanged;


    private void RaiseCollectionChanged(NotifyCollectionChangedEventArgs e)
    {
        if (this.CollectionChanged != null)
            this.CollectionChanged(this, e);
    }

    private void RaisePropertyChanged(PropertyChangedEventArgs e)
    {
        if (this.PropertyChanged != null)
            this.PropertyChanged(this, e);
    }


    event PropertyChangedEventHandler INotifyPropertyChanged.PropertyChanged
    {
        add { this.PropertyChanged += value; }
        remove { this.PropertyChanged -= value; }
    }
}

This calls INotifyCollectionChanged, does the same as a ObservableCollection, but in a stack manner.

Community
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Kevin
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  • Why does he need a stack? Can't he just simply `.Insert(0, item)` any new items in the beginning of the list? – ANeves Apr 02 '14 at 10:58
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    @ANeves, Because the mentioned insert is done in O(n) time, so it can be an expensive insert. – mslot Apr 14 '14 at 20:20
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    @mslot if that is the reason, it should be in the answer. – ANeves Apr 15 '14 at 00:05
  • I tried using this observable stack as a datasource for my listbox, but it doesn't work. Pushing items is not reflected on the listbox as observable collection usually do, any idea? – NadaNK Jun 24 '15 at 07:17
-2

you can try this

collection.insert(0,collection.ElementAt(collection.Count - 1));

Samet Dumankaya
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