Send Value from View Model to UserControl Dependency Property WPF - wpf

Question

I have a dependency property in a UserControl with a property called SelectedColor. From my main app, the view of the window that uses this my code is:
<controls:ColorPicker SelectedColor="{Binding MyCanvas.CanvasBackgroundColor}" />
And the code from the view model is:
public MyCanvas { get; set; }
public MyWindowViewModel(MyCanvas myCanvas)
{
MyCanvas = myCanvas;
}
And then the XAML for my UserControl is:
<UserControl . . .>
<Button Click="Button_Click">
<Button.Style>
<Setter Property="Background" Value="Transparent" />
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type Button}">
<Border Background="{Binding SelectedColor}" BorderBrush="Black" BorderThickness="1" />
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
</Button.Style>
</Button>
</UserControl>
And the code-behind:
public ColorPicker()
{
InitializeComponent();
DataContext = this;
}
public SolidColorBrush SelectedColor
{
get { return (SolidColorBrush)GetValue(SelectedColorProperty); }
set { SetValue(SelectedColorProperty, value); }
}
public static readonly DependencyProperty SelectedColorProperty =
DependencyProperty.Register(nameof(SelectedColor), typeof(SolidColorBrush), new UIPropertyMetadata(null));
I think the problem might be with the line in the code-behind DataContext = this;. Is it correct that declaring this creates an entirely new context for the instance of this user control in the main app and therefore any values sent to it from the view model would be re-initialized? If so, how can I send the value over without it being re-declared? I also need the DataContext = this line because without it some functionality within my UserControl will no longer work.
Has anyone encountered this before?
Thanks in advance!

Answer 1

DataContext = this sets the DataContext of the UserControl to itself. You don't want to do this. Instead you could bind to a property of the UserControl using a {RelativeSource} without setting the DataContext property:
<Border Background="{Binding SelectedColor, RelativeSource={RelativeSource AncestorType=UserControl}}"
BorderBrush="Black" BorderThickness="1" />
Code-behind:
public ColorPicker()
{
InitializeComponent();
}
public SolidColorBrush SelectedColor
{
get { return (SolidColorBrush)GetValue(SelectedColorProperty); }
set { SetValue(SelectedColorProperty, value); }
}
public static readonly DependencyProperty SelectedColorProperty =
DependencyProperty.Register(nameof(SelectedColor), typeof(SolidColorBrush), new UIPropertyMetadata(null));