Databases
StackOverflow2013
Postsdbo
POWhen Clearing an ObservableCollection, There are No Items in e.OldItems
Body
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POWhen Clearing an ObservableCollection, There are No Items in e.OldItems
    text
    copied!<p>I have something here that is really catching me off guard.</p> <p>I have an ObservableCollection of T that is filled with items. I also have an event handler attached to the CollectionChanged event.</p> <p>When you <strong>Clear</strong> 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. <strong>I would expect e.OldItems to be filled with all items that were removed from the collection.</strong></p> <p>Has anyone else seen this? And if so, how have they gotten around it?</p> <p>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.</p> <p><br></p> <p><strong>CLARIFICATION:</strong> I do know that the documentation doesn't <em>outright</em> 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.</p> <p><br></p> <p>Below is the sample code if you wish to reproduce it yourself. First off the xaml:</p> <pre><code>&lt;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" &gt; &lt;StackPanel&gt; &lt;Button x:Name="addButton" Content="Add" Width="100" Height="25" Margin="10" Click="addButton_Click"/&gt; &lt;Button x:Name="moveButton" Content="Move" Width="100" Height="25" Margin="10" Click="moveButton_Click"/&gt; &lt;Button x:Name="removeButton" Content="Remove" Width="100" Height="25" Margin="10" Click="removeButton_Click"/&gt; &lt;Button x:Name="replaceButton" Content="Replace" Width="100" Height="25" Margin="10" Click="replaceButton_Click"/&gt; &lt;Button x:Name="resetButton" Content="Reset" Width="100" Height="25" Margin="10" Click="resetButton_Click"/&gt; &lt;/StackPanel&gt; &lt;/Window&gt; </code></pre> <p>Next, the code behind:</p> <pre><code>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 { /// &lt;summary&gt; /// Interaction logic for Window1.xaml /// &lt;/summary&gt; 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&lt;int&gt; _integerObservableCollection = new ObservableCollection&lt;int&gt; { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 }; } } </code></pre>
 

Querying!

 
Guidance
An individual column

Larger individual text columns get their own page to allow for proper reading.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload