与排序列表的数据绑定

Question

My UI has a ListBox which is bound to a Collection. Right now this happens to be an ObservableCollection

My objective is to add objects to this Collection via the UI, and have the ListBox dynamically update, all while maintaining a sorted Collection.

I am aware that there is some SortedView that I can use in WPF. But that is not what I want - I need the actual Collection to remain sorted because my business logic requires a sorted collection.

One way that I thought of, is to create my own Collection class which uses a SortedList internally, and implements the INotifyCollectionChanged interface and produces NotifyCollectionChangedEventArgs event when the internal list changes. Sounds like a lot of work!

Is there a simple solution that I've missed?

Answer 1

Depending on your exact needs, the simplest approach is to keep your ObservableCollection, but wrap in in a new property of type ICollectionView:

public class MyViewModel {
  private CollectionViewSource _collectionViewSource;

  public ICollectionView MyCollectionView  => _collectionViewSource.View;

  public MyViewModel(ObservableCollection<MyDataItem> dataItems) {
      _collectionViewSource = new CollectionViewSource() { Items = dataItems };
      //Add sorting here using _collectionViewSource.SortDescriptions.Add(...)
  }

You can use the wrapper property to extract a sorted list as needed.

Answer 2

Okay so I ended up inheriting from ObservableCollection, and overriding the Add() method. This did the trick for me. Now my list is always sorted, and the ObservableCollection is the one that Notifies the UI of changes.

   public class MyCollection : ObservableCollection<Int32>
   {
      public new void Add(Int32 x)
      {
         base.Add(x);
         var oldList = new ObservableCollection<Int32>(this.OrderBy(c=>c));

         Clear();
         foreach(var i in oldList)
         {
            base.Add(i);
         }
      }
   }

I'm a beginner with C#, any feedback on the code is appreciated.