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WPF bind to property of the ItemsPanel of an ItemsControl

I've written a code example below:
<StackPanel>
<TextBlock>Appointments today</TextBlock>
<ItemsControl ItemsSource="{Binding Appointments}">
<ItemsControl.ItemsPanel>
<ItemsPanelTemplate>
<controls:CalendarMonthDayEventsItemsPanel OutsideViewportCount="..." />
</ItemsPanelTemplate>
</ItemsControl.ItemsPanel>
<ItemsControl.ItemTemplate>
<DataTemplate>
<Border>
<TextBlock Text="{Binding Title}" />
</Border>
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
<StackPanel Orientation="Horizontal">
<TextBlock>+</TextBlock>
<TextBlock Text="{Binding ......}" /> <!-- Should show number of items in ItemsControl that are outside view, using CalendarMonthDayEventsItemsPanel.OutsideViewportCount -->
<TextBlock>more items</TextBlock>
</StackPanel>
</StackPanel>
I Created a custom Panel, the CalendarMonthDayEventsItemsPanel, and I use that panel as the itemspanel of the ItemsControl. In the panel's layout code, I determine how many items (panel childs) are outside the bounds of the panel. The property OutsideViewportCount contains the number of items that are outside of the visible bounds of the CalendarMonthDayEventsItemsPanel.
Now I want to show the value of OutsideViewportCount in a TextBlock that's below the ItemsControl.
This means I have to create some kind of binding, but everything I tried doesn't work.
Does someone have a solution or a better approach to achieve the same result?

Maybe you can make use of Tag property of ItemsPanel to relay the value of ItemsPanel as a workaround.
<ItemsControl x:Name="A"
ItemsSource="{Binding Appointments}">
<ItemsControl.ItemsPanel>
<ItemsPanelTemplate>
<local:CalendarMonthDayEventsItemsPanel OutsideViewportCount="{Binding RelativeSource={RelativeSource AncestorType={x:Type ItemsControl}}, Path=Tag, Mode=OneWayToSource}"/>
</ItemsPanelTemplate>
</ItemsControl.ItemsPanel>
...
</ItemsControl>
<StackPanel Orientation="Horizontal">
<TextBlock>+</TextBlock>
<TextBlock Text="{Binding ElementName=A, Path=Tag, Mode=OneWay}"/>
<TextBlock>more items</TextBlock>
</StackPanel>

Can I use a WrapPanel to organize ListView group headers?

I would like to be able to use a WrapPanel to wrap by group header instead of by item.
I have implemented the following ICollectionView view for a ListView bound to an ObservableCollection studentlist:
view = CollectionViewSource.GetDefaultView(studentlist);
view.GroupDescriptions.Add(new PropertyGroupDescription("sectionoutput"));
view.SortDescriptions.Add(new SortDescription("sectionoutput", ListSortDirection.Ascending));
view.SortDescriptions.Add(new SortDescription("displayname", ListSortDirection.Ascending));
The XAML includes a style resource to set the template for the group header:
<Style x:Key="ContainerStyle" TargetType="{x:Type GroupItem}">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate>
<Expander Header="{Binding Name}" IsExpanded="{Binding Name, Mode=OneWay, Converter={StaticResource expanderconverter}}">
<ItemsPresenter />
</Expander>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
This Style is used as the GroupStyle for the ListView:
<ListView ScrollViewer.HorizontalScrollBarVisibility="Disabled">
<ListView.GroupStyle>
<GroupStyle ContainerStyle="{StaticResource ContainerStyle}"/>
</ListView.GroupStyle>
...
<ListView.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding displayname}">
</TextBlock>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
As is, the code presents a vertical list of student names grouped by a header listing their section number. But I would like to list the groups sequentially in a horizontal direction.
I know that I am able to organize the items in the ListView with a WrapPanel:
<ListView.ItemsPanel>
<ItemsPanelTemplate>
<WrapPanel Orientation="Horizontal" ItemWidth="150">
</WrapPanel>
</ItemsPanelTemplate>
</ListView.ItemsPanel>
But this code merely displays the students in a group side by side rather than displaying the groups themselves side by side. What I would like to do is have the groups themselves wrapped horizontally. I've tried to implement a wrap panel in the style resource, but I haven't been successful and have been wondering if there is a way to wrap by group.
I figure it is possible to do this by switching to a TreeView and turning the groups into Items. But I would prefer to use a ListView if at all possible because my program implements a class that takes the ListView as an argument.

The GroupStyle has a Panel property that you can set to an ItemsPanelTemplate with a WrapPanel:
<ListView.GroupStyle>
<GroupStyle ContainerStyle="{StaticResource ContainerStyle}">
<GroupStyle.Panel>
<ItemsPanelTemplate>
<WrapPanel />
</ItemsPanelTemplate>
</GroupStyle.Panel>
</GroupStyle>
</ListView.GroupStyle>

Suppose to have a ViewModel that is the DataContext of the XAML posted below that contains an ObservableCollection<GroupViewModel> named GroupsViewModel.
GroupViewModel merely has a property named GroupName that is the name of the Group to show and it has a property of ObservableCollection<StudentViewModel>.
StudentViewModel has the property displayName to display the name of the Student.
Said so, by using an Expander and 2 nested ListBox you can get what you asked, like the following code:
<ListBox ItemsSource="{Binding GroupsViewModel}">
<ListBox.ItemTemplate>
<DataTemplate>
<Grid>
<Expander HorizontalAlignment="Left" IsExpanded="True" Header="{Binding GroupName}">
<ListBox ItemsSource="{Binding StudentViewModel}" HorizontalAlignment="Left">
<ListBox.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding displayname}" />
</DataTemplate>
</ListBox.ItemTemplate>
<ListBox.ItemsPanel>
<ItemsPanelTemplate>
<StackPanel Orientation="Vertical"></StackPanel>
</ItemsPanelTemplate>
</ListBox.ItemsPanel>
</ListBox>
</Expander>
</Grid>
</DataTemplate>
</ListBox.ItemTemplate>
<ListBox.ItemsPanel>
<ItemsPanelTemplate>
<StackPanel Orientation="Horizontal"></StackPanel>
</ItemsPanelTemplate>
</ListBox.ItemsPanel>

Drawing multiple layers over wpf map control

I have the grid with wpf map control and canvas over it for drawing markers over map.
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="*"></RowDefinition>
</Grid.RowDefinitions>
<UserControl Grid.Row="0" Content="{Binding CurrentMap}" />
<UserControl Grid.Row="0" Content="{Binding DrawningCanvas}" />
</Grid>
Now I needed to use more than 1 layer over the map.
What wpf control I should use for binding to ObservableCollection<Canvas> in DataContext and draw them all over each other?

You seem to be somewhat confused. An ObservableCollection is a collection for data items. A Canvas is a UI control. Therefore, you should never have a data item collection with UI elements in.
Instead, you could have a Marker data class that contains X and Y properties for the marker's positions and maybe Name and ImageSource properties to define what it would look like in the UI. Then you could have a ObservableCollection of type Marker named Markers that you could bind to the ItemsSource property of an ItemsControl. Finally, you could set a Canvas as the ItemsPanel of the ItemsControl:
<ItemsControl ItemsSource="{Binding Markers}">
<ItemsControl.ItemsPanel>
<ItemsPanelTemplate>
<Canvas />
</ItemsPanelTemplate>
</ItemsControl.ItemsPanel>
<ItemsControl.ItemContainerStyle>
<Style TargetType="ContentPresenter">
<Setter Property="Canvas.Left" Value="{Binding X}"/>
<Setter Property="Canvas.Top" Value="{Binding Y}"/>
</Style>
</ItemsControl.ItemContainerStyle>
<ItemsControl.ItemTemplate>
<DataTemplate DataType="{x:Type YourXmlNamespacePrefix:Marker}">
<StackPanel Orientation="Horizontal">
<Image Source="{Binding ImageSource}" />
<TextBlock Text="{Binding Name}" />
</StackPanel>
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
I don't really know why you would want to have multiple layers because you could overlay multiple items on the same layer, but if you really need multiple layers, then you can just add more of the ItemsControl elements shown above.

Add extra element to ItemsControl's Canvas

I have an ItemsControl set up like this:
<Grid>
<ItemsControl ItemsSource="{Binding Asteroids}">
<ItemsControl.ItemsPanel>
<ItemsPanelTemplate>
<Canvas Background="Black">
<!-- i want to add another polygon to the canvas-->
<!--<Polygon Name ="ShipPolygon" Points="{Binding Ship}" Fill="Blue" />-->
</Canvas>
</ItemsPanelTemplate>
</ItemsControl.ItemsPanel>
<ItemsControl.ItemTemplate>
<DataTemplate>
<Polygon Fill="Gray" Points="{Binding AsteroidPoints}" />
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
</Grid>
As you can see, the ItemsControl is displaying a collection's elements as Polygons in a Canvas. But i also want to add another Polygon to this Canvas, here named "ShipPolygon". I can't do that this way, because i get an XMLParseException. What is the proper method to do this? Thanks in advance!

You are using an ItemsControl, which is there to display multiple similar items on an itemspanel.
Now obviously you can't add something to your ItemsPanelTemplate there you are only telling the itemscontrol which panel it should use to display its items.
Your ItemsSource and your ItemTemplate suggest that you only want to show Asteroids in your ItemsControl. So the easiest way would be to just overlay your ship onto the itemscontrol with your asteroids
<Grid>
<ItemsControl ItemsSource="{Binding Asteroids}">
<ItemsControl.ItemsPanel>
<ItemsPanelTemplate>
<Canvas Background="Black"/>
</ItemsPanelTemplate>
</ItemsControl.ItemsPanel>
<ItemsControl.ItemTemplate>
<DataTemplate>
<Polygon Fill="Gray" Points="{Binding AsteroidPoints}" />
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
<Polygon Name ="ShipPolygon" Points="{Binding Ship}" Fill="Blue" />
</Grid>
Otherwise you could add it aswell to the itemscontrol, but then need to use different ItemTemplates. And you need to handle, that your ItemsControl no longer only holds Asteroids.
Using implicit item Templates
<!-- No key, so it is implicit and automatically used-->
<DataTemplate DataType="{x:Type Asteroids}">
<Polygon Fill="Gray" Points="{Binding AsteroidPoints}" />
</DataTemplate>
<DataTemplate DataType="{x:Type Player}">
<Polygon Name ="ShipPolygon" Points="{Binding Ship}" Fill="Blue" />
</DataTemplate>
<!-- above must be in a resource section, like app.xaml -->
<Grid>
<ItemsControl ItemsSource="{Binding Entities}">
<ItemsControl.ItemsPanel>
<ItemsPanelTemplate>
<Canvas Background="Black"/>
</ItemsPanelTemplate>
</ItemsControl.ItemsPanel>
</ItemsControl>
</Grid>
Or you could use a DataTemplateSelector.

Binding a nested list to a WPF canvas panel

I was wondering if its possible to somehow bind a list of lists to a cavas panel. For example having object "layer" which itself is a list of "rectangle" objects. Would if be possible to bind a list of layers to a canvas? So far I can only do it by binding a flattened INumerable of the nested list (using SelectMany function) to an itemcontrol, but this isnt good enough, Id like to keep the "layers" separate and have the Zindex of the rectangles vary according to the layer it is at, allowing to reorder the layers easily.
I have also tried having nested itemcontrols but as expected it only displays the first layer. The aim is to draw a rectangle for every object in every layer on the canvas allowing for layer manipulation, insertion of new objects in each layer, etc...
Thanks in advance! :)

How about making the ItemTemplate of the main ItemsControl another ItemsControl with yet another Canvas as ItemsPanel? (I do not see a reason why it should only display the first layer)
Actually the main ItemsControl does not need to be a Canvas, a Grid would do as well (at least unless your collections have coordinates of their own or a Z-Order, if you use a grid the layer order is he same as their appearance in the collection).
An example (a bit verbose but can't do anything about that):
<ItemsControl ItemsSource="{Binding Data}">
<ItemsControl.ItemsPanel>
<ItemsPanelTemplate>
<Grid />
</ItemsPanelTemplate>
</ItemsControl.ItemsPanel>
<ItemsControl.ItemTemplate>
<DataTemplate>
<ItemsControl ItemsSource="{Binding LayerItems}">
<ItemsControl.ItemsPanel>
<ItemsPanelTemplate>
<Canvas />
</ItemsPanelTemplate>
</ItemsControl.ItemsPanel>
<ItemsControl.ItemContainerStyle>
<Style TargetType="{x:Type ContentPresenter}">
<!-- Here would the binding to some properties that take care of placement -->
<Setter Property="Canvas.Top" Value="{Binding Top}" />
<Setter Property="Canvas.Left" Value="{Binding Left}" />
</Style>
</ItemsControl.ItemContainerStyle>
<ItemsControl.ItemTemplate>
<!-- Some template for the individual items -->
<DataTemplate>
<Border Padding="5" BorderThickness="1" BorderBrush="Red" CornerRadius="3"
Background="White">
<TextBlock Text="{Binding Name}" />
</Border>
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>

Like H.B said, i too can't see a reason why it will not work. Having an ItemsControl in another ItemsContainer works perfectly fine.
<ItemsControl ItemsSource="{Binding Layers}">
<ItemsControl.ItemsContainerStyle>
<Style>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate>
<ItemsControl ItemsSource="{Binding Rectangles}"/>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
<ItemsControl.ItemsContainerStyle>
</ItemsControl>
But it think it would be cleaner to put the sub ItemsControl inside an DataTemplate for your Items, without the need to modify the ItemsContainerStyle. I think its bad design if your control needs to know informations about the properties of the model, which is necessary for binding to Rectangles.