WPF binding with .NET object not communicating the data - wpf

Question

I am following a tutorial on WPF data binding. I am trying to bind to a .NET object's property to a XAML control but the control does not display the expected data. These are what I believe to be the relevant sections of code:
In procedural code: (Note: removed ObservableCollection in PhotoGallery after original post)
Namespace PhotoGallery
Partial Public Class MainWindow
Inherits Window
Private photos As New Photos
...
End Class
Namespace PhotoGallery
Public Class Photos
Inherits Collection(Of Photo)
...
End Class
In XAML (Solution/Project name is Ch13-PhotoGallery):
<Window x:Class="PhotoGallery.MainWindow"
...
xmlns:local="clr-namespace:Ch13_PhotoGallery.PhotoGallery"
...>
<Window.Resources>
<local:Photos x:Key="Photos"/>
</Window.Resources>
And this is the control that is not displaying the data, which is the size of the Photos collection:
<Label x:Name="numItemsLabel" Background="AliceBlue" FontSize="8" Content="{Binding Source={StaticResource Photos}, Path=Count}"/>
When I typed in the < Label >, Intellisense popped up 'Count' for the Path property, so I think that tells me I have everything defined correctly.
If I add this line of procedural code behind to the refresh() method:
numItemsLabel.Content = photos.Count
Then the count is displayed correctly.
But I'm not getting the binding in XAML to display Photos.Count.

Answer 1

This creates a new instance of the Photos class:
<local:Photos x:Key="Photos"/>
If you want to bind to the Photos collection that you have created in your MainWindow.xaml.vb file you should expose it as a public property - you can only bind to properties but not fields - and set the DataContext of the window to an instance of the class where this property is defined, i.e. the window class itself in your case:
Class MainWindow
Public Property Photos As Photos
Public Sub New()
' This call is required by the designer.
InitializeComponent()
DataContext = Me
...
End Sub
End Class
You can the bind directly to the property:
<Label x:Name="numItemsLabel" Background="AliceBlue" FontSize="8" Content="{Binding Path=Photos.Count}"/>

Answer 2

Your ViewModel needs to implement the INotifyPropertyChanged interface, this will let your window listen to changes to your ViewModel
Here's an example of how to implement this interface in VB
https://social.msdn.microsoft.com/Forums/vstudio/en-US/7de44362-8b88-4292-b4ee-0385c3b34d7d/im-just-looking-for-a-simple-vb-net-mvvm-sample-wpf?forum=wpf
ViewModel
Public Class ViewModel
Implements INotifyPropertyChanged
Public Sub New()
Me.myTextValue = "default value..."
End Sub
Private myTextValue As String = String.Empty
Public Property MyTextProperty() As String
Get
Return Me.myTextValue
End Get
Set(ByVal value As String)
Me.myTextValue = value
NotifyPropertyChanged("MyTextProperty")
End Set
End Property
Public Event PropertyChanged As PropertyChangedEventHandler _
Implements INotifyPropertyChanged.PropertyChanged
Private Sub NotifyPropertyChanged(ByVal propertyName As String)
RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs(propertyName))
End Sub
End Class
XAML
<Window x:Class="MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="MainWindow" Height="350" Width="525">
<Grid>
<TextBox Text="{Binding MyTextProperty}"/>
</Grid>
</Window>
XAML Code Behind
Class MainWindow
Sub New()
' This call is required by the designer.
InitializeComponent()
' Add any initialization after the InitializeComponent() call.
Me.DataContext = New ViewModel()
End Sub
End Class