How to successfully implement WPF textbox validation?

Question

I'm trying to implement what should be simple textbox validation for a WPF application, but I'm having some problems.

I used this guide: http://www.codeproject.com/Tips/690130/Simple-Validation-in-WPF

My textbox in MainWindow.xaml:

     <TextBox x:Name="textbox1" HorizontalAlignment="Left" Height="23" 
             Margin="93,111,0,0" TextWrapping="Wrap" VerticalAlignment="Top" 
             Width="120" Style="{StaticResource textBoxInError}"
             Validation.ErrorTemplate="{StaticResource validationErrorTemplate}">
        <TextBox.Text>
            <Binding Path="Name" UpdateSourceTrigger="PropertyChanged">
                <Binding.ValidationRules>
                    <local:NameValidator/>
                </Binding.ValidationRules>
            </Binding>
        </TextBox.Text>
    </TextBox>

My NameValidator Class in MainWindow.xaml.cs:

    public class NameValidator : ValidationRule 
    {
      public override ValidationResult Validate(object value, System.Globalization.CultureInfo cultureInfo)
      {
        if (value == null)
            return new ValidationResult(false, "value cannot be empty.");
        else
        {
            if (value.ToString().Length > 3)
                return new ValidationResult(false, "Name cannot be more than 3 characters long.");
        }
        return ValidationResult.ValidResult;
      }
  }

My Static Resources in App.xaml:

        <ControlTemplate x:Key="validationErrorTemplate">
            <DockPanel>
                <TextBlock Foreground="Red" DockPanel.Dock="Top">!</TextBlock>
                <AdornedElementPlaceholder x:Name="ErrorAdorner"></AdornedElementPlaceholder>
            </DockPanel>
        </ControlTemplate>
        <Style x:Key="textBoxInError" TargetType="{x:Type TextBox}">
            <Style.Triggers>
                <Trigger Property="Validation.HasError" Value="true">
                    <Setter Property="ToolTip"
                            Value="{Binding RelativeSource={x:Static RelativeSource.Self},
                            Path=(Validation.Errors)[0].ErrorContent}"/>
                </Trigger>
            </Style.Triggers>
        </Style>

I can run the application without any errors, but the validation is never triggered.

Which part isn't working? The trigger? The Validation Method? etc — bill
– bill, Commented Jun 10, 2015 at 16:58
Sorry my problem was poorly worded. I updated the question with a screencast. No validation is firing at all, and there are no errors when I start my application. — user4681776
– user4681776, Commented Jun 10, 2015 at 17:03
I'm looking at the code you provided, and perhaps I'm blind but I do not see any code that subscribes to any of the text box control events (lostfocus, textchanged, etc) How are you triggering the validation when you type in the textbox? — bill
– bill, Commented Jun 10, 2015 at 17:09
Hey bill, I've tried PropertyChanged and LostFocus, but neither are giving me any results. <Binding Path="Name" UpdateSourceTrigger="PropertyChanged">. This is supposed to be in Textbox.Text in the binding tag, correct? — user4681776
– user4681776, Commented Jun 10, 2015 at 17:10
Are you sure "PropertyChanged" fires when you type text in the textbox? The sample tutorial you linked is using lostfocus. If you try that event instead, does it work? — bill
– bill, Commented Jun 10, 2015 at 17:11

Theodosius Von Richthofen · Accepted Answer · 2015-06-10 17:12:35Z

6

Using what you posted, it works fine for me, it produces the red "!" above the textbox. However, I DID remember to set my DataContext, ie.

public MainWindow()
    {
        InitializeComponent();
        this.DataContext = this;
    }

Without this, it won't work.

answered Jun 10, 2015 at 17:12

Theodosius Von Richthofen

2,4992 gold badges25 silver badges46 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

user4681776 Over a year ago

Wow. Thanks. That did it, I'm just a n00b.

Collectives™ on Stack Overflow

How to successfully implement WPF textbox validation?

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related