WinRT Selectively hide a child of a ListViewItem based on the ListViewItem's sibling - winrt-xaml

Question

I am using a ListView and set the ItemsSources to an ObservableCollection of Message objects. The DataTemplate for the ListViewItem contains a custom control. I have defined a Message property on the custom control and am binding the Message property on this custom control to the dataContext of the ListViewItem. When the loaded event gets fired on the custom control, I want to compare the ReceivedDate set on its Message to the ReceivedDate set on the sibling of this ListViewItem. This is not working consistently since the Message property is set on some of the ListViewItems by the time the Loaded event is fired and not set on some.
Example:
<local:ListView x:Name="MyMessagesView"
Visibility="Collapsed"
ItemsSource="{Binding Messages}"
ItemContainerStyle="{StaticResource AppListViewItemStyle}">
<ListView.ItemTemplate>
<DataTemplate>
<dm:MyScreenRow Message="{Binding}"/>
</DataTemplate>
</ListView.ItemTemplate>
</local:ListView>
In the code behind of my CustomControl, I handle the Loaded event. I want to compare the ReceivedTime property set on the current ListViewItem to its previous sibling and show a child element in the ListViewItem. Is Loaded event not the correct place to handle this? If not, any recommendations on how to handle this?
public MyScreenRow()
{
this.InitializeComponent();
this.Loaded += MyScreenRow_Loaded;
}
private static void MyScreenRow_Loaded(object sender, RoutedEventArgs e)
{
MyScreenRow screenRow = sender as MyScreenRow;
if (screenRow.Message == null)
{
return;
}
ListViewItemPresenter presenter = (ListViewItemPresenter)VisualTreeHelper.GetParent(screenRow);
if (presenter != null)
{
ListViewItem currentViewItem = (ListViewItem)VisualTreeHelper.GetParent(presenter);
if (currentViewItem != null)
{
ListView listView = (ListView)ItemsControl.ItemsControlFromItemContainer(currentViewItem);
if (listView != null)
{
int indexOfCurrentContainer = listView.IndexFromContainer(currentViewItem);
if (indexOfCurrentContainer == 0)
{
screenRow.GroupHeader.Visibility = Visibility.Visible;
}
else
{
// Get the previous container info
ListViewItem previousViewItem = (ListViewItem)listView.ContainerFromIndex(indexOfCurrentContainer - 1);
if (previousViewItem != null)
{
MyScreenRow previousScreenRow = (MyScreenRow)previousViewItem.ContentTemplateRoot;
if (previousScreenRow != null
&& previousScreenRow.Message != null
&& previousScreenRow.Message.ReceivedTimeUtc != null)
{
if (screenRow.Message != null
&& screenRow.Message.ReceivedTimeUtc != null)
{
if (previousScreenRow.Message.ReceivedTimeUtc.Date.CompareTo(screenRow.Message.ReceivedTimeUtc.Date) != 0)
{
screenRow.GroupHeader.Visibility = Visibility.Visible;
}
}
}
}
}
}
}
}
}

Answer 1

Yes.. as you guessed doing it in the loaded event will not work becuase the loaded event is fired only Once when the listview is first instantiated and loaded with some elements after that it isn't fired.
I strongly suggest you use the LayoutUpdated Event .
This is a part of UIElement so every control in the windows universe must have it.
it is triggered when there is a layout change .. in case of lists when new items are added or deleted ..
Now to some more fun part .. if you don't want to do it all your controls at once then you can use ContainerContentChanging this will allow you to apply changes on the items in view only.
<ListView LayoutUpdated="ListView_LayoutUpdated" ContainerContentChanging="ListView_ContainerContentChanging"/>
Quick tutorial link : http://blogs.msdn.com/b/hanxia/archive/2013/11/04/incremental-update-item-data-for-listviewbased-controls-in-windows-8-1.aspx