问题描述
我这里有些东西真的让我措手不及.
I have something here that is really catching me off guard.
我有一个T的ObservableCollection，其中已填充项目.我还为CollectionChanged事件附加了一个事件处理程序.
I have an ObservableCollection of T that is filled with items. I also have an event handler attached to the CollectionChanged event.
清除集合时，它将导致CollectionChanged事件，其e.Action设置为NotifyCollectionChangedAction.Reset.好吧，那很正常.但是奇怪的是e.OldItems或e.NewItems都没有任何内容. 我希望e.OldItems会填充从集合中删除的所有项目.
When you Clear the collection it causes an CollectionChanged event with e.Action set to NotifyCollectionChangedAction.Reset. Ok, that's normal. But what is weird is that neither e.OldItems or e.NewItems has anything in it. I would expect e.OldItems to be filled with all items that were removed from the collection.
还有其他人看到过吗?如果是这样，他们如何解决呢?
Has anyone else seen this? And if so, how have they gotten around it?
某些背景:我正在使用CollectionChanged事件来附加和分离另一个事件，因此，如果我在e.OldItems中没有任何项目……我将无法从该事件分离.
Some background: I am using the CollectionChanged event to attach and detach from another event and thus if I don't get any items in e.OldItems ... I won't be able to detach from that event.
说明:我确实知道文档并没有完全声明必须采用这种方式.但是对于其他所有动作，它都会通知我已完成的操作.因此，我的假设是...在清除/重置的情况下也会告诉我.
CLARIFICATION:I do know that the documentation doesn't outright state that it has to behave this way. But for every other action, it is notifying me of what it has done. So, my assumption is that it would tell me ... in the case of Clear/Reset as well.
下面是示例代码，如果您想自己重现它.首先是xaml:
Below is the sample code if you wish to reproduce it yourself. First off the xaml:
<Window
x:Class="ObservableCollection.Window1"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="Window1"
Height="300"
Width="300"
>
<StackPanel>
<Button x:Name="addButton" Content="Add" Width="100" Height="25" Margin="10" Click="addButton_Click"/>
<Button x:Name="moveButton" Content="Move" Width="100" Height="25" Margin="10" Click="moveButton_Click"/>
<Button x:Name="removeButton" Content="Remove" Width="100" Height="25" Margin="10" Click="removeButton_Click"/>
<Button x:Name="replaceButton" Content="Replace" Width="100" Height="25" Margin="10" Click="replaceButton_Click"/>
<Button x:Name="resetButton" Content="Reset" Width="100" Height="25" Margin="10" Click="resetButton_Click"/>
</StackPanel>
</Window>
接下来，后面的代码:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
using System.Collections.ObjectModel;
namespace ObservableCollection
{
/// <summary>
/// Interaction logic for Window1.xaml
/// </summary>
public partial class Window1 : Window
{
public Window1()
{
InitializeComponent();
_integerObservableCollection.CollectionChanged += new System.Collections.Specialized.NotifyCollectionChangedEventHandler(_integerObservableCollection_CollectionChanged);
}
private void _integerObservableCollection_CollectionChanged(object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
{
switch (e.Action)
{
case System.Collections.Specialized.NotifyCollectionChangedAction.Add:
break;
case System.Collections.Specialized.NotifyCollectionChangedAction.Move:
break;
case System.Collections.Specialized.NotifyCollectionChangedAction.Remove:
break;
case System.Collections.Specialized.NotifyCollectionChangedAction.Replace:
break;
case System.Collections.Specialized.NotifyCollectionChangedAction.Reset:
break;
default:
break;
}
}
private void addButton_Click(object sender, RoutedEventArgs e)
{
_integerObservableCollection.Add(25);
}
private void moveButton_Click(object sender, RoutedEventArgs e)
{
_integerObservableCollection.Move(0, 19);
}
private void removeButton_Click(object sender, RoutedEventArgs e)
{
_integerObservableCollection.RemoveAt(0);
}
private void replaceButton_Click(object sender, RoutedEventArgs e)
{
_integerObservableCollection[0] = 50;
}
private void resetButton_Click(object sender, RoutedEventArgs e)
{
_integerObservableCollection.Clear();
}
private ObservableCollection<int> _integerObservableCollection = new ObservableCollection<int> { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 };
}
}
推荐答案
好吧，尽管我仍然希望ObservableCollection的行为符合我的期望……下面的代码才是我最终要做的.基本上，我创建了一个名为TrulyObservableCollection的T的新集合，并覆盖了ClearItems方法，然后使用该方法引发了Clearing事件.
Ok, even though I still wish that ObservableCollection behaved as I wished ... the code below is what I ended up doing. Basically, I created a new collection of T called TrulyObservableCollection and overrided the ClearItems method which I then used to raise a Clearing event.
在使用该TrulyObservableCollection的代码中，我使用此Clearing事件循环遍历那时仍在集合中的项目 ，以完成我希望分离的事件的分离来自.
In the code that uses this TrulyObservableCollection, I use this Clearing event to loop through the items that are still in the collection at that point to do the detach on the event that I was wishing to detach from.
希望这种方法也可以帮助其他人.
Hope this approach helps someone else as well.
public class TrulyObservableCollection<T> : ObservableCollection<T>
{
public event EventHandler<EventArgs> Clearing;
protected virtual void OnClearing(EventArgs e)
{
if (Clearing != null)
Clearing(this, e);
}
protected override void ClearItems()
{
OnClearing(EventArgs.Empty);
base.ClearItems();
}
}
这篇关于清除ObservableCollection时，e.OldItems中没有项目的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！