UserControl doesn't show validation exception in Silverlight

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.???

What do you mean by 'when the user control gets a validation exception'? — Luke Woodward

ibebbs ibebbs · Accepted Answer · 2011-10-11T19:11:30

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.

UserControl doesn't show validation exception in Silverlight

1 Answers