C#中ObservableCollection的CollectionChanged事件

Question

C#中ObservableCollection的CollectionChanged事件

4

如何优化这段代码：

void CollectionChanged(object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
{
    if (sender is ObservableCollection<PromotionPurchaseAmount>)
    {
        if (e.Action == NotifyCollectionChangedAction.Remove)
        {
            foreach (PromotionPurchaseAmount item in e.NewItems)
            {
                //Removed items
                item.PropertyChanged -= EntityViewModelPropertyChanged;
            }
        }
        else if (e.Action == NotifyCollectionChangedAction.Add)
        {
            foreach (PromotionPurchaseAmount item in e.NewItems)
            {
                //Added items
                item.PropertyChanged += EntityViewModelPropertyChanged;
            }
        }
    }
    else if (sender is ObservableCollection<PromotionItemPricing>)
    {
        if (e.Action == NotifyCollectionChangedAction.Remove)
        {
            foreach (PromotionItemPricing item in e.NewItems)
            {
                //Removed items
                item.PropertyChanged -= EntityViewModelPropertyChanged;
            }
        }
        else if (e.Action == NotifyCollectionChangedAction.Add)
        {
            foreach (PromotionItemPricing item in e.NewItems)
            {
                //Added items
                item.PropertyChanged += EntityViewModelPropertyChanged;
            }
        }
    }
    else if (sender is ObservableCollection<PromotionItem>)
    {
        if (e.Action == NotifyCollectionChangedAction.Remove)
        {
            foreach (PromotionItem item in e.NewItems)
            {
                //Removed items
                item.PropertyChanged -= EntityViewModelPropertyChanged;
            }
        }
        else if (e.Action == NotifyCollectionChangedAction.Add)
        {
            foreach (PromotionItem item in e.NewItems)
            {
                //Added items
                item.PropertyChanged += EntityViewModelPropertyChanged;
            }
        }
    }
}

- Seied Ali

你具体在寻找什么？代码是否无法正常工作？也许将其发布到http://codereview.stackexchange.com会更合适。 - Dan J

1

帮了我，不确定为什么被关闭了。 - Todd Main

2

帮了我很多，我不认为它太局限了。 - Eric

1个回答

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- Daniel Hilgarth · Accepted Answer

When e.Action == NotifyCollectionChangedAction.Remove you need to iterate over e.OldItems instead of e.NewItems.
When e.Action == NotifyCollectionChangedAction.Replace you need to iterate over e.OldItems to remove the event handler from the old items and you need to iterate over e.NewItems to add the event handler to the new items.

Refactor the code like this:

if (sender is ObservableCollection<PromotionPurchaseAmount> || 
    sender is ObservableCollection<PromotionItemPricing> || 
    sender is ObservableCollection<PromotionItem>)
{
    if (e.Action == NotifyCollectionChangedAction.Remove ||
        e.Action == NotifyCollectionChangedAction.Replace)
    {

        foreach (INotifyPropertyChanged item in e.OldItems)
        {
            //Removed items
            item.PropertyChanged -= EntityViewModelPropertyChanged;
        }
    }
    if (e.Action == NotifyCollectionChangedAction.Add ||
        e.Action == NotifyCollectionChangedAction.Replace)
    {
        foreach (INotifyPropertyChanged item in e.NewItems)
        {
            //Added items
            item.PropertyChanged += EntityViewModelPropertyChanged;
        }
    }
}

这是可行的，因为您所有的促销类都实现了INotifyPropertyChanged接口。