c#中observablecollection的CollectionChanged事件

本文关键字：CollectionChanged 事件 observablecollection | 更新日期: 2023-09-27 18:07:48

如何把这段代码写得更好:

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;
            }
        }
    }
}

当e.Action == NotifyCollectionChangedAction.Remove需要迭代e.OldItems而不是e.NewItems时。
当e.Action == NotifyCollectionChangedAction.Replace时，您需要迭代e.OldItems以从旧项目中删除事件处理程序，并且您需要迭代e.NewItems以向新项目添加事件处理程序。

这样重构代码:

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;
        }
    }
}

这个可以工作，因为你所有的Promotion类都实现了INotifyPropertyChanged