WPF ValidationRule and Validation.Error does not raise event - wpf

Question

What's wrong with these code, the Validation.Error is never fired whereas I setthe and the NotifyOnValidationError property to True. So, the method "Grid_Error(object sender, ValidationErrorEventArgs e)" is never executed, but I don't know why :(
<Window xmlns:my="clr-namespace:WpfDigitalClock;assembly=WpfDigitalClock" x:Class="WpfApplication1.MainWindow"
xmlns:local="clr-namespace:WpfApplication1"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="MainWindow" Height="350" Width="525">
<Window.Resources>
<local:Names x:Key="MyNames" />
</Window.Resources>
<Grid Validation.Error="Grid_Error">
<TextBox Height="21" Margin="12,62,0,0" Name="TextBox1" VerticalAlignment="Top" HorizontalAlignment="Left" Width="120">
<TextBox.Text>
<Binding Source="{StaticResource MyNames}" Path="FirstName" NotifyOnValidationError="True">
<Binding.ValidationRules>
<local:StringValidator />
</Binding.ValidationRules>
</Binding>
</TextBox.Text>
</TextBox>
<TextBox Height="21" HorizontalAlignment="Right" Margin="0,62,12,0" Name="TextBox2" VerticalAlignment="Top" Width="120" >
<TextBox.Text>
<Binding Source="{StaticResource MyNames}" Path="LastName" NotifyOnValidationError="True">
<Binding.ValidationRules>
<local:StringValidator />
</Binding.ValidationRules>
</Binding>
</TextBox.Text>
</TextBox>
<Button HorizontalAlignment="Left" Margin="35,122,0,116" Name="Button1" Width="75" Click="Button1_Click">Back</Button>
<Button HorizontalAlignment="Right" Margin="0,122,34,117" Name="Button2" Width="75" Click="Button2_Click">Forward</Button>
<Button Height="22" Margin="101,0,101,56" Name="Button3" VerticalAlignment="Bottom" Click="Button3_Click">Add</Button>
</Grid>
in the Window1.xaml.cs file :
public class StringValidator : ValidationRule
{
public override ValidationResult Validate(object value,
System.Globalization.CultureInfo cultureinfo)
{
string aString = value.ToString();
if (aString == "")
return new ValidationResult(false, "String cannot be null");
return new ValidationResult(true, null);
}
}
private void Grid_Error(object sender, ValidationErrorEventArgs e)
{
if(e.Action == ValidationErrorEventAction.Added)
MessageBox.Show(e.Error.ErrorContent.ToString());
}
Thank you for your help !
EDIT :
Here my Names Class :
class Names : ObservableCollection<Name>
{
public Names ()
{
Name aName = new Name("FirstName " + (this.Count +1).ToString(),
"LastName " + (this.Count + 1).ToString());
this.Add(aName);
}
}
Here my Name class :
class Name : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
private string _firstName;
private string _lastName;
public Name(string fName, string lName)
{
_firstName = fName;
_lastName = lName;
}
public string FirstName
{
get
{
return _firstName;
}
set
{
_firstName = value;
PropertyChanged(this, new PropertyChangedEventArgs("FirstName"));
}
}
public string LastName
{
get
{
return _lastName;
}
set
{
_lastName = value;
PropertyChanged(this, new PropertyChangedEventArgs("LastName"));
}
}
}

Answer 1

The application cannot modify the content of this collection. See the Example section for an example of how to use this attached property.
The WPF data binding model enables you to associate ValidationRules with your Binding object. Validation occurs during binding target-to-binding source value transfer before the converter is called. The following describes the validation process:
1.When a value is being transferred from the target property to the source property, the data binding engine first removes any ValidationError that may have been added to the Validation.Errors attached property of the bound element. It then checks if there are any custom ValidationRules defined for that Binding, in which case it calls the Validate method on each of the ValidationRules until one of them runs into an error or until all of them pass.
2.Once there is a custom rule that does not pass, the binding engine creates a ValidationError object and adds it to the Validation.Errors collection of the bound element. When Validation.Errors is not empty, the Validation.HasError attached property of the element is set to true. Also, if the NotifyOnValidationError property of the Binding is set to true, then the binding engine raises the Validation.Error attached event on the element.
3.If all of the rules pass, the binding engine then calls the converter, if one exists.
4.If the converter passes, the binding engine calls the setter of the source property.
5.If the binding has an ExceptionValidationRule associated with it and an exception is thrown during step
4, the binding engine checks to see if there is a UpdateSourceExceptionFilter. You have the option to use the UpdateSourceExceptionFilter callback to provide a custom handler for handling exceptions. If an UpdateSourceExceptionFilter is not specified on the Binding, the binding engine creates a ValidationError with the exception and adds it to the Validation.Errors collection of the bound element.
Also note that a valid value transfer in either direction (target-to-source or source-to-target) clears the Validation.Errors attached property.
For information about the behavior of this property in MultiBinding scenarios, see ValidationError.

Answer 2

From your comment i would conclude that the ValidationRule does not return an error, hence the error event is not fired. Try stepping through the Validation-method with the debugger.
Also, validation is only performed upon a source-update, in TextBoxes that normally happens on LostFocus.
Edit: MyNames is a collection, it not have the properties you try to bind to, there should be binding errors in the Output window.
If you want to bind to the first element you need to change the path to something like [0].LastName for the last-name-binding.

Answer 3

Does your Names class implement INotifyPropertyChanged?
In the code-behind file of the file, set your datacontext to this. Expose your Names object as a property there and see if that works. I'm not comfortable with binding to the static resource in the window.