I have a UserControl that will be reused throughout an application we are developing.
We are using a framework based on MVVMLight.

For the sake of simplicity lets say the user control contains only one textbox and exposes one dependency property named "Quantity". The textbox on the user control is databound to the dependency property "Quantity".

When the user control is used on a view, the "Quantity" dependency property of the usercontrol is databound to a property in a ViewModel. (This ViewModel is the datacontext of our view by way of the MVVMLight ViewModelLocator).

This all works great! The bindings work, properties are set like I would expect. All is well until it comes to validation.

We are using DataAnnotations to decorate our ViewModel properties. The ViewModel contains a custom implementation of INotifyDataErrorInfo. We have implemented custom styles for most input controls to show a red border around the control, and a message next to the control displaying the validation error message. All of this works great in a normal case (eg. Textbox on a View bound to a property in a view model).

When I attempt the same approach using this user control, what I end up with is a red border around the entire user control and no error indication on the actual textbox. It appears that the fact that there is an error is being reflected in the UI, but it's just not making it to the control I want it to.

I've searched on stackoverflow for this problem, of those questions with solutions, none seem to work for my situation.

My first guess is that because the actual textbox is bound directly to the dependency property itself and not the property on my view model, it is not being notified properly of the errors generated. Is there some way to propogate those errors generated in the viewmodel through the usercontrol and then to the textbox?

Any help or suggestions you can give would be great, thanks.

Here is the UserControl xaml.

```
<UserControl x:Class="SampleProject.UserControls.SampleControl"
         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
         xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
         xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
         mc:Ignorable="d"  x:Name="sampleControl"
         d:DesignHeight="300" d:DesignWidth="300">
<Grid x:Name="LayoutRoot" DataContext="{Binding ElementName=sampleControl}">
        <TextBox Text="{Binding Path=Quantity, ValidatesOnDataErrors=True}" Width="100" Height="30" />
</Grid>
</UserControl>

```

The UserControl code behind.

```
public partial class SampleControl : UserControl
{
    public SampleControl()
    {
        InitializeComponent();
    }

    public static readonly DependencyProperty QuantityProperty = 
         DependencyProperty.Register("Quantity", typeof(int?), typeof(SampleControl), 
    new FrameworkPropertyMetadata{DefaultValue=null, BindsTwoWayByDefault = true});

    public int? Quantity
    {
        get { return (int?)GetValue(QuantityProperty); }
        set { SetValue(QuantityProperty, value); }
    }
}

```

Used on a view.

```
<userControls:SampleControl Grid.Row="1" Quantity="{Binding Path=Quantity, ValidatesOnDataErrors=True}" Height="60" Width="300"/>

```

The ViewModel property.

```
[Required(ErrorMessage = "Is Required")]
[Range(5, 10, ErrorMessage = "Must be greater than 5")]
public int? Quantity
{
    get { return _quantity; }
    set { Set(() => Quantity, ref _quantity, value); }
}
private int? _quantity;

```

(\*Note, The Set method in the setter is just a helper method in the base viewmodel that sets the backing property and raises the PropertyChanged event for it.)