WPF label binding not updating properly - wpf

Question

I know there are a thousand questions on the topic, but I cannot find what's wrong with mine...
I have a .xaml.cs file with the standard notify property changed stuff, a public member with the "notify" in the setter. I also set the data context in the constructor. Looks like this:
public partial class SlimERDplot : UserControl
{
public SlimERDplot()
{
DataContext = this;
InitializeComponent();
}
public enum AvailableImaginations { NotSet, Right, Left}
private AvailableImaginations _movementImagination = AvailableImaginations.NotSet;
//This is the one I'll be binding
public string HemisphereUI { get { return Hemisphere.ToString() + " hemisphere"; } }
public AvailableHemispheres Hemisphere
{
get { return _hemisphere; }
set
{
if (_hemisphere != value)
{
_hemisphere = value;
NotifyPropertyChanged();
NotifyPropertyChanged("HemisphereUI"); //tried with or without this,
//makes no difference
}
}
}
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void NotifyPropertyChanged([CallerMemberName] String propertyName = "")
{
var handler = PropertyChanged;
if (handler != null)
handler(this, new PropertyChangedEventArgs(propertyName));
}
}
The XAML simply:
<Label HorizontalAlignment="Right" Content="{Binding Path=HemisphereUI}"></Label
Then from the consumer XAML I use it like this:
<UIControls:SlimERDplot x:Name="ERDRightDown" Hemisphere="Right" MovementImagination="Left" />
But in the label, it always says NotSet (the default value). I debugged, and the thing does get through the setter with the proper value, but the displayed value is never changed
What's missing?

Answer 1

What's missing?
Your UserControl doesn't implement INotifyPropertyChanged:
public partial class SlimERDplot : UserControl, INotifyPropertyChanged
{
...
}
This is required for the view to actually subscribe to the PropertyChanged event.

Answer 2

You have to use DependencyProperty
Here an example
CodeBehind
public partial class MyUserControl : UserControl
{
public MyUserControl()
{
InitializeComponent();
}
public string HemisphereUI
{
get { return (string)GetValue( HemisphereUIProperty ); }
private set { SetValue( HemisphereUIProperty, value ); }
}
// Using a DependencyProperty as the backing store for HemisphereUI. This enables animation, styling, binding, etc...
public static readonly DependencyProperty HemisphereUIProperty =
DependencyProperty.Register( nameof( HemisphereUI ), typeof( string ), typeof( MyUserControl ), new PropertyMetadata( null ) );
public AvailableHemispheres Hemisphere
{
get { return (AvailableHemispheres)GetValue( HemisphereProperty ); }
set { SetValue( HemisphereProperty, value ); }
}
// Using a DependencyProperty as the backing store for Hemisphere. This enables animation, styling, binding, etc...
public static readonly DependencyProperty HemisphereProperty =
DependencyProperty.Register( nameof( Hemisphere ), typeof( AvailableHemispheres ), typeof( MyUserControl ), new PropertyMetadata( AvailableHemispheres.NotSet, OnHemisphereChanged ) );
private static void OnHemisphereChanged( DependencyObject d, DependencyPropertyChangedEventArgs e )
{
MyUserControl control = ( d as MyUserControl )!;
control.HemisphereUI = e.NewValue.ToString() + " hemisphere";
}
}
public enum AvailableHemispheres
{
NotSet,
Right,
Left,
}
XAML
<UserControl
x:Class="WpfApp1.Views.MyUserControl"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:local="clr-namespace:WpfApp1.Views"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
d:DesignHeight="450"
d:DesignWidth="800"
mc:Ignorable="d">
<Grid>
<Label
HorizontalAlignment="Center"
VerticalAlignment="Center"
Content="{Binding HemisphereUI, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type local:MyUserControl}}}" />
</Grid>
</UserControl>