更改集合时触发方法

Question

I have a binding that uses this collection:

private RangeObservableCollection<Item> _allItems;

public RangeObservableCollection<Item> AllItems
            { 
                get { return _allItems; }
                set { _allItems = value; }
            }

RangeObservarbleCollection is a collection that throws only one notification that the collection was changed when AddRange method is called.

I have another collection whose items depend on the items of the AllItems collection.

private RangeObservableCollection<Item> _commonItems;

I want whenever the AllItems collection gets changed to fire a method that does some calculations and changes the items in the CommonItems collection. I tried to fire it inside the set method for the AllItems collection but the Value is of type collection not of type Item.

Answer 1

You can attach an event on to the collection like this:

_allItems.CollectionChanged += new NotifyCollectionChangedEventHandler(_allItems_CollectionChanged)

protected void _allItems_CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
{
     switch (e.Action)
         {
             case NotifyCollectionChangedAction.Add:
                //do stuff;
                 break;
             case NotifyCollectionChangedAction.Remove:
                //do stuff
                 break;
         }

}

Answer 2

You will want to attach to the event on the AllItems collection when setting the property, and detach when clearing it. Then fire your event from within the handler for the AllItems event.

 public RangeObservableCollection<Item> AllItems { get { return _allItems; } set { if (_allItems != null) { _allItems.CollectionChanged -= AllItems_CollectionChanged; } _allItems = value; } if (_allItems != null) { _allItems.CollectionChanged +-= AllItems_CollectionChanged; } } private void AllItems_CollectionChanged(object sender, CollectionChangedEventArgs e) { OnCollectionChanged(e); } private void OnCollectionChanged(CollectionChangedEventArgs args) { EventHandler<CollectionChangedEventArgs> temp = CollectionChanged; if (temp != null) { temp.Invoke(this, args); } }