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How to bind to a source inside a ListBox different from the ItemsSource already specified

I have a ListBox inside a HubSection, whose Items are bound to a class "players" added to my DefaulViewModel via code behind.
First I simply put a TextBox bound to the property "PlayerName" of my class "players".
Now I would like to add a ComboBox with some items that are NOT part of the class players.
Is it possible ? I thought that definind an ItemsSource in the ComboBox would sort of override the ItemsSource of the ListBox, but nothing displays.
The DataContext of the whole page is defined like so:
DataContext="{Binding DefaultViewModel, RelativeSource={RelativeSource Self}}"
Then the HubSection is like so:
<HubSection x:Name="HubSec1">
<DataTemplate>
<ListBox x:Name="ListBox1" ItemsSource="{Binding players}">
<ListBox.ItemTemplate>
<DataTemplate>
<StackPanel>
<TextBox Text="{Binding Path=PlayerName, Mode=TwoWay}"/>
<ComboBox ItemsSource="{Binding Path=ListOfElements}"/>
</StackPanel>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
</DataTemplate>
</HubSection>
If I define the ComboBox in the same way but outside the ListBox, it will display the string elements of "ListOfElements" properly.
But in this ListBox, the ComboBox is empty. So my guess is that having defined an ItemsSource for the ListBox, it is not possible to override it.
I have tried to define a DataTemplate but was not successful doing so, but it might be the good solution (and I did not proceed properly)
What am I missing ?
Edit :
The ComboBox items is an ObservableCollection. It is not part of the "players" class.
Here is how I added these elements to the DefaultViewModel
DefaultViewModel.Add("players", players);
DefaultViewModel.Add("MyItemsList", ListOfElements);

You can walk up the visual tree and bind to an ancestors datacontext:
{Binding Path=PathToProperty, RelativeSource={RelativeSource AncestorType={x:Type typeOfAncestor}}}
EX:
{Binding Path=ListOfItems, RelativeSource={RelativeSource AncestorType={x:Type ListBox}}}
that should give you the datacontext that the listbox has, so assuming your ListOfItems exists in that data context.
Or you can name your control, and then bind to its datacontext by element name:
{Binding ElementName=mySourceElement,Path=ListOfItems}

It can be a little bit tricky to create a good working binding in Windows Apps. A widely used work around is to use the Tag property.
<ListBox x:Name="ListBox1" ItemsSource="{Binding players}" Margin="0,184,0,0" Tag="{Binding Path=ListOfElements}">
<ListBox.ItemTemplate>
<DataTemplate>
<StackPanel>
<TextBox Text="{Binding Path=PlayerName, Mode=TwoWay}"/>
<TextBox Text="{Binding Path=Tag, ElementName=ListBox1}"/>
</StackPanel>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
A binding to an element wirh the specific name will work always. And the ListOfElements should be in the scope of the ListBox so you can use the Tag property as a proxy. If you need to bind more than one property, you can also use dummy XAML elements:
<Border Tag="{Binding ...}" Name="dummy1"/>

Hide last item in a ItemsControl

I've a ItemsControl that I bind to my viewmodel, but inside the datatemplate I also have an image. I want that image to be visible as long as it's not the last item in the list, then it should be hidden (it's an arrow that point down to the next control).
The xaml look like this:
<ItemsControl ItemsSource="{Binding PageContainers}" x:Name="Items">
<ItemsControl.ItemTemplate>
<DataTemplate>
<StackPanel>
<controls:DesignControl DataContext="{Binding}" MouseDown="UIElement_OnMouseDown" MouseUp="UIElement_OnMouseUp" MouseMove="UIElement_OnMouseMove"/>
<Image Source="/Resources/Images/arrow.png" Height="16" Width="16" Margin="0,10,0,0"/>
</StackPanel>
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
So is there any easy to check if the Image/Stackpanel is last in the list? I guess I could subscribe to some event and do it in the code behind, but I guess it's cleaner if I could do it inside the xaml.

You're binding to PageContainers which I assume to be a collection. Can the type of that collection be extended to include an IsLast property?
If it can, you can bind the visibility to that.

How to access an item in a DataTemplate?

I defined a ListView like this:
<ListView x:Name="libraryBooksListView"
AutomationProperties.AutomationId="VideoListView"
AutomationProperties.Name="Videos"
TabIndex="1"
Padding="0,0,4,0"
ItemsSource="{Binding}"
IsSwipeEnabled="False"
ItemTemplate="{StaticResource LibraryBooksItemTemplate}"
ItemContainerStyle="{StaticResource LibraryListViewItemStyle}"
Grid.Column="1"
SelectionMode="None">
</ListView>
and I defined the LibraryBooksItemTemplate like this:
<DataTemplate x:Key="LibraryBooksItemTemplate">
<Grid Margin="0">
<GridView x:Name="booksGridView"
AutomationProperties.AutomationId="ItemGridView"
AutomationProperties.Name="Grouped Items"
ItemsSource="{Binding Items}"
ItemTemplateSelector="{StaticResource textbookTemplateSelector}"
SelectionMode="Multiple"
IsItemClickEnabled="True"
ItemClick="booksGridView_ItemClick"
SelectionChanged="booksGridView_SelectionChanged"
IsSwipeEnabled="false"
ScrollViewer.VerticalScrollBarVisibility="Auto">
<GridView.ItemsPanel>
<ItemsPanelTemplate>
<WrapGrid Orientation="Horizontal" />
</ItemsPanelTemplate>
</GridView.ItemsPanel>
</GridView>
</Grid>
</DataTemplate>
The GridView, booksGridView, has multiple items (books).
How to modify/access the "ItemTemplateSelector" and SelectionMode etc. of the GridView?
Is there a way to access each of the items in the booksGridView?
Thx

There are many ways to do that.
The easiest one is to wrap your DataTemplate contents into a UserControl.
Another one is to use something like ContainerFromIndex().
Then you can also use VisualTreeHelper class to walk the visual tree.
Then again you can subclass your ItemsControl and override GetContainerForItemOverride() or
PrepareContainerForItemOverride() or
use the ItemContainerGenerator property
The imporant thing to note is that your ItemsSource provides items to the control while the overrides or the generator provide containers to display the items using the ItemTemplates.
*Edit As for your additional questions:
How to modify/access the "ItemTemplateSelector" and SelectionMode etc. of the GridView?
You have defined your selector resource and gave it a key of "textbookTemplateSelector", so you can just get it with this.Resources["textbookTemplateSelector"]. SelectionMode you can bind to the same source DataContext you bound your ItemsSource to and change or read it through a binding.
Is there a way to access each of the items in the booksGridView?
Yes. Since your DataContext is set as the ItemsSource of your ListView - you can access all the items through that DataContext. Each of these items seems to have an Items property that is bound to your GridView, so you can access each of these through the Items property you have defined yourself.

You can access it by using ItemsSource:
foreach(var book in this.booksGridView.ItemsSource)
{
}

bind item's children control in ItemsControl wpf

i am binding an ItemsControl to a list, but in item template there is a control which is not binding by current dataSource, i want to bind it with another dataSource.
but i am stuck at accessing that control
my ItemsControl's dataTemplate is--->
<ItemsControl x:Name="ItemRequesterList" IsTabStop="False">
<ItemsControl.ItemTemplate>
<DataTemplate x:Name="ItemReqTemplate">
<StackPanel Margin="10,0,0,0">
<TextBlock Text="{Binding DisplayName}"></TextBlock>
<TextBlock Text="requested on"></TextBlock>
<TextBlock Text="{Binding}"></TextBlock> //<---this control, i
// want to bind with another dataSource
</StackPanel>
</DataTemplate>
so how can i access this control, which is lie in each item ?

You could bind the DataContext of that control to some static resource, for example:
<TextBlock Text="{Binding}" DataContext="{StaticResource myOtherContext}"></TextBlock>
See the following:
Silverlight - Setting DataContext in XAML rather than in constructor?

WPF: Accessing two DataContexts in the same control

I am using an MVVM approach, and I have an object from my ViewModel called DatabasesSubFrame which is DataTemplated to show a ListBox. I want to display a Button below the ListBox, which binds to both the currently SelectedItem, and a property on the DatabasesSubFrame object which is being DataTemplated.
I know how to refer to the currently selected item, by setting the DataContext on a shared ancestor with the ListBox and use {Binding /}. In this example the shared ancestor is a StackPanel. And if the DataContext wasn't explicitly set there I could easily bind to a property on the DatabasesSubFrame object by just doing {Binding SomeProperty}. However, if I do {Binding SomeProperty} within the explicitly set DataContext, it refers to the wrong DataContext.
How do I access the "original" DataContext here? I tried messing with RelativeSources and TemplatedParents but couldn't figure out how to fit them in.
<DataTemplate DataType="{x:Type VM:DatabasesSubFrame}">
<StackPanel DataContext="{Binding Databases}" >
<ListBox Name="DbInfoBox"
ItemsSource="{Binding}"
IsSynchronizedWithCurrentItem="True">
<ListBox.ItemTemplate>
<DataTemplate>
<Label Content="{Binding ShortName}"/>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
<!-- Problem: The Command and V:CreateCommandBinding.Command are set incorrectly here. How do I access OpenDbCommand from the top-level DataTemplate's DataContext? -->
<Button Content="Open Database"
CommandParameter="{Binding /}"
Command="{Binding ???, Path=OpenDbCommand.Command}"
V:CreateCommandBinding.Command="{Binding ???, Path=DataContext.OpenDbCommand}"/>
</StackPanel>
</DataTemplate>

I think this question will help you to find the answer to yours. Another trick is to set the Name of the Window to something like "Root". You can then get at the window's original datacontext by using:
{Binding ElementName=Root, Path=DataContext.MyViewModelsProperty}