UserControl doesn't show validation exception in Silverlight - wpf

Question

I have a user control and I have bound its dependency property TextValue to a View Model RightSpecGlassStrength
UserControl code
<UserControl x:Class="NumericUpDown1"
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:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
mc:Ignorable="d"
d:DesignHeight="25" d:DesignWidth="70">
<StackPanel Orientation="Horizontal" VerticalAlignment="Top" >
<TextBox x:Name="InputTextBox" Grid.Row="0" Grid.Column="0" Grid.RowSpan="1"
Style="{StaticResource NumericUpDownTextBoxStyle}"
KeyDown="InputTextBox_KeyDown"
KeyUp="InputTextBox_KeyUp"
GotFocus="InputTextBox_GotFocus"
LostFocus="InputTextBox_LostFocus"
MouseWheel="InputTextBox_MouseWheel"
MouseEnter="InputTextBox_MouseEnter"
TextInputStart="InputTextBox_TextInputStart"
LayoutUpdated="InputTextBox_LayoutUpdated"
/>
</StackPanel>
</UserControl>
ViewItems.Xaml
<userControl:NumericUpDown1 x:Name="RightSpecGlassStrengthUpDown" Maximum="28" Minimum="-28" Step="0.25" TextValue="{Binding RightSpecGlassStrength, Mode=TwoWay, ValidatesOnNotifyDataErrors=True, NotifyOnValidationError=True}" TabIndex="5" />
ViewItemsViewModel.cs
public class ViewItemsViewModel : EntityViewModel
{
#region constructor
public ViewItemsViewModel(){}
#endregion
#region properties
private Double rightSpecGlassStrength;
public Double RightSpecGlassStrength
{
get
{
return rightSpecGlassStrength;
}
set
{
rightSpecGlassStrength=value;
ValidateStrengths("RightSpecGlassStrength", RightSpecGlassStrength);
PropertyChangedHandler("RightSpecGlassStrength");
}
}
private void ValidateStrengths(string propertyName1, double RightSpecGlassStrength)
{
ClearErrorFromProperty(propertyName1);
if (RightSpecGlassStrength == 0)
AddErrorForProperty(propertyName1, "Value can not be 0");
}
#endregion
}
My EntityViewModel.cs is implementing INotifyDataErrorInfo interface and inherit ViewModelBase class
public class EntityViewModel : ViewModelBase, INotifyDataErrorInfo
{
}
ViewModelBase.cs implements INotifyPropertyChanged
public class ViewModelBase : INotifyPropertyChanged
{
}
My code works fine when I bind the textbox or other silverlight control to the viewmodel.
and shows proper validation exception on the control.
But when the user control gets a validation exception the control does not show any exception.
I'm not getting whats wrong with user control.???

Answer 1

It's difficult to fully debug the issue without the code behind for the user control, however, it seems to me that you have a dependency property on the code behind like this:
public static DependencyProperty TextValueProperty = DependencyProperty.Register("TextValue", typeof(string), typeof(NumericUpDown1), null)
You then seem to be using the TextInputStart, KeyDown, KeyUp events to capture changes to the underlying control. My hunch is that either:
a) You're failing to update the TextValue property to the new value.
b) Your code behind is interfering with the validation process.
I would suggest that, instead of code behind, you name the user control in the xaml; i.e.
<UserControl x:Class="NumericUpDown1" x:Name="View"> ... </UserControl>
Then bind the text value of the underlying TextBox directly to the dependency property, like this:
<TextBox Text="{Binding ElementName=View, Path=TextValue, Mode=TwoWay, ValidatesOnNotifyDataErrors=True, NotifyOnValidationError=True}" ... />
This should then allow the validation mechanism to proceed as normal.
Hope it helps.