CODEWITHSUNDEEP
c#wpf
james pearce
james pearce

Reputation: 365

My first C# WPF ValidationRule is not firing

I am trying learn how to implement data validation but my first attempt is not firing the lblSource_Error event; does anyone know what I have missed?

My Window's XAML:

<Window x:Class="cCompleteWPFResourcesExamples.wValidationRule"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="clr-namespace:cCompleteWPFResourcesExamples"
    Title="wValidationRule" Height="300" Width="300">
<Window.Resources>
    <local:Customer x:Key="rCustomer" Forename="InXaml" Surname="Created" ID="1"     
AmountOutstanding="0"/>
</Window.Resources>
<StackPanel x:Name="stkMain" DataContext="{StaticResource rCustomer}">
    <Label x:Name="lblSource" Validation.Error="lblSource_Error">
        <Label.Content>
            <Binding Path="ID" NotifyOnValidationError="True">
                <Binding.ValidationRules>
                    <local:cIDValidationRule/>
                </Binding.ValidationRules>
            </Binding>
        </Label.Content>
    </Label>
    <Label x:Name="lblErrorMessage" Content="No Error Yet"/>
</StackPanel>
</Window>

My Window's code:

   namespace cCompleteWPFResourcesExamples
    {
    /// <summary>
    /// Interaction logic for wValidationRule.xaml
    /// </summary>
    public partial class wValidationRule : Window
    {
        Customer cus = new Customer();

        public wValidationRule()
        {
            InitializeComponent();
            cus.ID = 0;
            stkMain.DataContext = cus;
        }


        private void lblSource_Error(object sender, ValidationErrorEventArgs e)
        {
            lblErrorMessage.Content = e.Error.ErrorContent.ToString();
        }
    }
    }

My ValidationRule:

using System.Windows.Controls;

namespace cCompleteWPFResourcesExamples 
{
public class cIDValidationRule : ValidationRule
{
    public override ValidationResult Validate(object value, 
System.Globalization.CultureInfo cultureInfo)
    {
        int iValue = (int)value;
        if (iValue == 0) return new ValidationResult(false, "No ID number");

        return new ValidationResult(true, null);
    }
}
}

The Customer object is very simple: Just a few properties.

Thanks!

James

Upvotes: 3

Views: 3756

Answers (2)

Squirrel5853
Squirrel5853

Reputation: 2406

I had to do this to get it working for me, which I got from this site

<Binding Path="ID" 
NotifyOnValidationError="True" 
ValidatesOnDataErrors="true" 
ValidatesOnExceptions="True" 
UpdateSourceTrigger="PropertyChanged" Mode="TwoWay">

hope this helps, also watch out as the object that gets passed through to validation was a string in my case not an int

public override ValidationResult Validate(object value, System.Globalization.CultureInfo cultureInfo)
{
    if (value is int)
    {
        int iValue = (int)value;
        if (iValue == 0) 
        {
            return new ValidationResult(false, "No ID number");
        }

        return new ValidationResult(true, null);
    }
    else if (value is string)
    { 
        string strValue = (string)value;
        if (String.IsNullOrEmpty(strValue) || strValue == "0")
        { 
            return new ValidationResult(false, "No ID number"); 
        }
    }

    return new ValidationResult(true, null);
}

* Update **

I forgot I also had to add this in for it to trigger

public wValidationRule()
{
    InitializeComponent();
    cus.ID = 0;
    stkMain.DataContext = cus;

    //trigger the validation.
    lblSource.GetBindingExpression(Label.ContentProperty).UpdateSource();
}

Upvotes: 0

dev hedgehog
dev hedgehog

Reputation: 8791

Awww such a sad title :) :) First wpf validationrule is not doing what you want.

The binding engine checks each ValidationRule associated with a binding each time an input value (the binding target property value) is transferred to the binding source property.

Remember this:

You type something and the value is being persisted to the source => ValidationRule will fire.

You want to show something in Label and the value is being transmitted from source to Label => ValidationRule will never fire.

If you wish your example to work then take a TextBox instead and set the Binding Mode to TwoWay so you may type in something and Binding will persist the typed value to the source causing ValidationRule to fire. :)

Upvotes: 2

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