CODEWITHSUNDEEP
c#wpfvalidationxamlmvvm
user7849697
user7849697

Reputation: 597

Validation when pressing button

I created validation in WPF with the help of a ValidationRule :

public class EmptyValidationRule : ValidationRule
{
    public override ValidationResult Validate(object value, CultureInfo cultureInfo)
    {
        if (!string.IsNullOrEmpty(value.ToString()))
        {
            return new ValidationResult(true, null);
        }

        return new ValidationResult(false, "Dit veld is verplicht.");
    }
}

And I use it like this :

<StackPanel Grid.Column="1"
            Grid.Row="0"
            Margin="10 0 0 20">
    <TextBox Width="200"
             Height="30"
             HorizontalAlignment="Left"
             VerticalContentAlignment="Center">
        <TextBox.Text>
            <Binding Path="Product.ProductName" Mode="TwoWay" UpdateSourceTrigger="LostFocus">
                <Binding.ValidationRules>
                    <validators:EmptyValidationRule ValidationStep="RawProposedValue" />
                </Binding.ValidationRules>
            </Binding>
        </TextBox.Text>
        <Validation.ErrorTemplate>
            <ControlTemplate>
                 <StackPanel>
                     <!-- Placeholder for the TextBox itself -->
                     <AdornedElementPlaceholder x:Name="textBox"/>
                     <TextBlock Text="{Binding [0].ErrorContent}" Foreground="Red"/>
                 </StackPanel>
            </ControlTemplate>
        </Validation.ErrorTemplate>
    </TextBox>
</StackPanel>

It works but not as expected. For example if the windows is loaded and you use Tab to jump to the next field the message is not shown. But when I type in the field and then remove it it shows the message.

Start up :

enter image description here

If I click in the TextBox and press Tab no message is shown :

enter image description here

If I click again in the first TextBox and type something and then remove it again and pres Tab, the message is shown :

enter image description here

How can I fix this? Or how can I show the message when I click on the button?

Upvotes: 0

Views: 254

Answers (1)

mm8
mm8

Reputation: 169160

Set the ValidatesOnTargetUpdated property of the ValidationRule to true:

 <validators:EmptyValidationRule ValidatesOnTargetUpdated="True" ValidationStep="RawProposedValue" />

Or update the source of the binding explicitly in your button click event handler or another one, like for example LostFocus:

textBox.GetBindingExpression(TextBox.TextProperty).UpdateSource();

Don't forget to check if value is null before you call ToString() on it in your validation rule:

if (!string.IsNullOrEmpty(value?.ToString()))

Upvotes: 1

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