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POValidationRules not removing error when value is set back to valid value
 

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    <p><strong>INTRODUCTION</strong></p> <p>I have created a <em>DecimalTextBox</em> <code>UserControl</code> that houses some decimal validation I need done, so that I dont need to recreate the validation each time, and can just use the <code>UserControl</code> instead. This validation has properties that need to be bound to, and so I have created <code>DependencyProperties</code> so I can bind to them, according to <a href="http://www.codeproject.com/Articles/18678/Attaching-a-Virtual-Branch-to-the-Logical-Tree-in" rel="nofollow">this article by Josh Smith</a>.</p> <hr> <p><strong>THE PROBLEM</strong></p> <p>The control's validation is behaving strangely. When I type an erroneous value into the <code>TextBox</code>, it shows up as an error. However when I try to change the value back <em>in the code</em> the value shown in the textbox remains unchanged.</p> <p>Here are the steps I perform that cause this error (in this example 1 is an invalid value):</p> <ol> <li>Load the form and the default value is <strong>0</strong>.</li> <li>Enter <strong>1</strong> into the textbox (and the textbox goes <strong>red</strong> due to the validation result being and error)</li> <li><em>In the code</em> I set the property bound to the textbox to <strong>0</strong></li> <li>The form still displays <strong>1</strong> in a <strong>red</strong> textbox</li> </ol> <hr> <p><strong>CODE EXAMPLE</strong></p> <p>I prepaired an example demonstrating the problem, which can be downloaded <a href="https://docs.google.com/open?id=0B9JOiSJxT9vjZDExMWY4MWUtNTc5YS00ZmM0LTlkOGItOGRiNmUwMDE3NGM1" rel="nofollow">here.</a></p> <p>I'll post some of the code here, if you want more let me know.</p> <p><strong>ValidationTestControl's XAML</strong></p> <pre><code>&lt;UserControl x:Class="WPFTestProject.ValidationTestControl" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:v="clr-namespace:WPFTestProject" x:Name="ValidationTest" Height="50" Width="525"&gt; &lt;Grid&gt; &lt;Grid.RowDefinitions&gt; &lt;RowDefinition&gt;&lt;/RowDefinition&gt; &lt;/Grid.RowDefinitions&gt; &lt;StackPanel Orientation="Horizontal" VerticalAlignment="Center" HorizontalAlignment="Center"&gt; &lt;TextBlock Text="Type 'Banana' here: "&gt;&lt;/TextBlock&gt; &lt;TextBox MinWidth="100"&gt; &lt;TextBox.Text&gt; &lt;Binding ElementName="ValidationTest" Path="Text" UpdateSourceTrigger="PropertyChanged" Mode="TwoWay" ValidatesOnDataErrors="True" ValidatesOnExceptions="True"&gt; &lt;Binding.ValidationRules&gt; &lt;v:NotBananaValidationRule&gt; &lt;v:NotBananaValidationRule.NotWhatBinding&gt; &lt;v:NotBananaBinding x:Name="NotBananaValidationBinding"&gt;&lt;/v:NotBananaBinding&gt; &lt;/v:NotBananaValidationRule.NotWhatBinding&gt; &lt;/v:NotBananaValidationRule&gt; &lt;/Binding.ValidationRules&gt; &lt;/Binding&gt; &lt;/TextBox.Text&gt; &lt;/TextBox&gt; &lt;TextBlock Text=" (the text will give error when = 'Banana')"&gt;&lt;/TextBlock&gt; &lt;/StackPanel&gt; &lt;/Grid&gt; </code></pre> <p></p> <p><strong>ValidationTestControls Code Behind</strong> </p> <p>(yes I know not very MVVM but I felt it was ok for this stand alone control)</p> <pre><code> public partial class ValidationTestControl : UserControl { public ValidationTestControl() { InitializeComponent(); Banana = "Banana"; Binding BananaBinding = new Binding("Banana"); BananaBinding.Source = this; NotBananaValidationBinding.SetBinding(NotBananaBinding.NotWhatProperty, BananaBinding); } public static DependencyProperty TextProperty = DependencyProperty.Register("Text", typeof(string), typeof(ValidationTestControl), new PropertyMetadata()); public static DependencyProperty BananaProperty = DependencyProperty.Register("Banana", typeof(string), typeof(ValidationTestControl), new PropertyMetadata()); public string Text { get { return (string)GetValue(TextProperty); } set { SetValue(TextProperty, value); } } public string Banana { get { return (string)GetValue(BananaProperty); } set { SetValue(BananaProperty, value); } } } </code></pre> <p><strong>ValidationRule and FrameWorkElement created for binding</strong></p> <pre><code> public class NotBananaValidationRule:ValidationRule { private NotBananaBinding _notWhatBinding; public NotBananaBinding NotWhatBinding { get { return _notWhatBinding; } set { _notWhatBinding = value; } } public override ValidationResult Validate(object value, System.Globalization.CultureInfo cultureInfo) { string what = value.ToString(); if(what == _notWhatBinding.NotWhat||string.IsNullOrEmpty(what)) return new ValidationResult(false, "Please enter a string that is not " + _notWhatBinding.NotWhat); else return new ValidationResult(true, null); } } public class NotBananaBinding : FrameworkElement { public static readonly DependencyProperty NotWhatProperty = DependencyProperty.Register( "NotWhat", typeof(string), typeof(NotBananaBinding), new UIPropertyMetadata()); public string NotWhat { get { return (string)GetValue(NotWhatProperty); } set { SetValue(NotWhatProperty, value); } } public NotBananaBinding() { } } </code></pre> <p>Basically what this code does is check if you have typed "Banana" and then returns a validation error. The control exposes dependency properties because I want to be able to bind to them when I use the control. The <code>FrameworkElement</code> <em>NotBananaBinding</em> lets me create dependency properties (because it is a <code>DependencyObject</code> so i can bind stuff for the validation. The ValidationRule has a <em>NotBananaBinding</em> property that stores the dependency property and uses it in the validate method.</p> <p>I know my property names are kinda crappy, sorry. The thing is that the example does a good job of displaying the error. In my haste to make an example I didn't name the variables very well. If you find the code crappy <strong>please download the sample</strong> <a href="https://docs.google.com/open?id=0B9JOiSJxT9vjZDExMWY4MWUtNTc5YS00ZmM0LTlkOGItOGRiNmUwMDE3NGM1" rel="nofollow">here.</a></p> <hr> <p><strong>WHAT I'VE FIGURED OUT SO FAR</strong></p> <p>Basically this problem seems to be caused by the fact that I am <em>not actually changing the value</em>.</p> <p>Even if I call OnPropertyChanged on the property, because the value is not different it doesn't try and reevaluate the Validation.</p> <p>I can obviously change the value to some arbitrary Valid value and then change it to the one I want it to be and it will work, but I was hoping there is some way to get call validation manually, to reevaluate the value and then change it etc. The changing it away and back is kinda messy.</p> <hr> <p><strong>CONCLUSION</strong></p> <p>Am I doing something wrong (perhaps something about the way I implemented the validation and binding from Josh Smiths post) </p> <p>Is this just a c# bug, or is the behavior intended? If so then why?</p> <p>Are there any elegant ways to fix it?</p> <p>u_u</p>
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    1. COPosting code really helps - people don't want to run sample projects. Try to reduce the problem to the minimum possible code that reproduces the problem. You never know, you might solve the problem yourself.
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    2. COOk I'll post the code.
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