ValidationRule and DependencyObject - wpf

Question

I need to send Binding values to a ValidationRule. I am using a DependencyObject, but the values are always null.
Here is my DependencyObject
public class MyDependencyObject : DependencyObject
{
public string BindingValue
{
get { return (string)GetValue(BindingValueProperty); }
set { SetValue(BindingValueProperty, value); }
}
public static readonly DependencyProperty BindingValueProperty =
DependencyProperty.Register("BindingValue", typeof(string), typeof(MyDependencyObject), new UIPropertyMetadata(null));
}
Here is my ValidationRule:
public class MyTextBoxValidationRule : ValidationRule
{
private MyDependencyObject _TxtVal;
public MyDependencyObject TxtVal
{
get { return _TxtVal; }
set { _TxtVal = value; }
}
public override ValidationResult Validate(object value, System.Globalization.CultureInfo cultureInfo)
{
//Validation Logic
}
}
Here is the XAML:
<TextBox >
<TextBox.Text>
<Binding Path="DataUserTypes"
NotifyOnValidationError="True"
ValidatesOnDataErrors="True"
Mode="TwoWay"
UpdateSourceTrigger="PropertyChanged"
NotifyOnSourceUpdated="True"
NotifyOnTargetUpdated="True"
Delay="100">
<Binding.ValidationRules>
<local:MyTextBoxValidationRule ValidatesOnTargetUpdated="True" >
<local:MyTextBoxValidationRule.TxtVal >
<local:MyDependencyObject
TxtVal="{Binding Path=ValidateValue}" />
</local:MyTextBoxValidationRule.TxtVal>
</local:MyTextBoxValidationRule>
</Binding.ValidationRules>
</Binding>
</TextBox.Text>
</TextBox>
When I step through Validate in MyTextBoxValidationRule TxtVal.BindingValue is always null. I have no idea why
edit:
I changed DisplayValue to DataUserTypes as there seems to be some confusion.
<Binding Path="DataUserTypes"
That is the binding for the Text value of the textbox. I need to validate DataUserTypes based on the property ValidateValue. I am trying to do that with the DependencyObject TxtVal.
I also fixed a copy and paste type. There was a field called TextValID that should have been TxtVal. Sorry about that.

Answer 1

<local:MyTextBoxValidationRule ValidatesOnTargetUpdated="True" >
<local:MyTextBoxValidationRule.TxtVal >
<local:MyDependencyObject
BindingValue="{Binding ValidateValue, PresentationTraceSources.TraceLevel=High}"
/>
</local:MyTextBoxValidationRule.TxtVal>
</local:MyTextBoxValidationRule>
PresentationTraceSources.TraceLevel=High produces the following trace output in the VS Output pane:
System.Windows.Data Warning: 56 : Created BindingExpression (hash=24230272) for Binding (hash=28316044)
System.Windows.Data Warning: 58 : Path: 'ValidateValue'
System.Windows.Data Warning: 60 : BindingExpression (hash=24230272): Default mode resolved to OneWay
System.Windows.Data Warning: 61 : BindingExpression (hash=24230272): Default update trigger resolved to PropertyChanged
System.Windows.Data Warning: 62 : BindingExpression (hash=24230272): Attach to Lines.MyDependencyObject.BindingValue (hash=37689768)
System.Windows.Data Warning: 64 : BindingExpression (hash=24230272): Use Framework mentor <null>
System.Windows.Data Warning: 67 : BindingExpression (hash=24230272): Resolving source
System.Windows.Data Warning: 69 : BindingExpression (hash=24230272): Framework mentor not found
System.Windows.Data Warning: 65 : BindingExpression (hash=24230272): Resolve source deferred
'Lines.exe' (CLR v4.0.30319: Lines.exe): Loaded 'C:\Windows\Microsoft.Net\assembly\GAC_MSIL\PresentationFramework.Aero\v4.0_4.0.0.0__31bf3856ad364e35\PresentationFramework.Aero.dll'. Skipped loading symbols. Module is optimized and the debugger option 'Just My Code' is enabled.
System.Windows.Data Warning: 67 : BindingExpression (hash=24230272): Resolving source
System.Windows.Data Warning: 69 : BindingExpression (hash=24230272): Framework mentor not found
Long story short, that instance of local:MyDependencyObject has no place to inherit a DataContext from, because its parent isn't in the visual tree.
You could use a BindingProxy to work around that, but what are you binding to? ValidateValue must be a property of something; but of what? If it's a property of the parent viewmodel, this will do it:
<TextBox.Resources>
<local:BindingProxy
x:Key="ViewmodelProxy"
Data="{Binding}"
/>
</TextBox.Resources>
<TextBox.Text>
<Binding Path="DataUserTypes"
NotifyOnValidationError="True"
ValidatesOnDataErrors="True"
Mode="TwoWay"
UpdateSourceTrigger="PropertyChanged"
NotifyOnSourceUpdated="True"
NotifyOnTargetUpdated="True"
Delay="100">
<Binding.ValidationRules>
<local:MyTextBoxValidationRule ValidatesOnTargetUpdated="True" >
<local:MyTextBoxValidationRule.TxtVal>
<local:MyDependencyObject
BindingValue="{Binding Data.ValidateValue, Source={StaticResource ViewmodelProxy}}"
/>
</local:MyTextBoxValidationRule.TxtVal>
</local:MyTextBoxValidationRule>
</Binding.ValidationRules>
</Binding>
</TextBox.Text>
Binding proxy:
public class BindingProxy : Freezable
{
#region Overrides of Freezable
protected override Freezable CreateInstanceCore()
{
return new BindingProxy();
}
#endregion
public object Data
{
get { return (object)GetValue(DataProperty); }
set { SetValue(DataProperty, value); }
}
// Using a DependencyProperty as the backing store for Data. This enables animation, styling, binding, etc...
public static readonly DependencyProperty DataProperty =
DependencyProperty.Register("Data", typeof(object), typeof(BindingProxy), new UIPropertyMetadata(null));
}