Ad

Using Validation In WPF With Dependency Property And Style Triggers

- 1 answer

I am trying to use Validation in WPF. I created a NotNullOrEmptyValidationRule as shown below:

public class NotNullOrEmptyValidationRule : ValidationRule
    {
        public override ValidationResult Validate(object value, CultureInfo cultureInfo)
        {
            if (String.IsNullOrEmpty(value as String))
                return new ValidationResult(false, "Value cannot be null or empty");

            return new ValidationResult(true, null); 
        }
    }

Now, I need to use it in my application. In my App.xaml file I declared the Style for the TextBox. Here is the declaration.

 <Style x:Key="textBoxStyle" TargetType="{x:Type TextBox}">

            <Setter Property="Background" Value="Green"/>

            <Style.Triggers>

                <Trigger Property="Validation.HasError" Value="True">

                    <Setter Property="Background" Value="Red"/>
                    <Setter Property="ToolTip" Value="{Binding RelativeSource={RelativeSource Self},Path=(Validation.Errors)[0].ErrorContent}"/>

                </Trigger>

            </Style.Triggers>

        </Style>

Now, I want to use it on my TextBox so I am using the following code:

  <TextBox Style="{StaticResource textBoxStyle}">
                <TextBox.Text>
                    <Binding>
                        <Binding.ValidationRules>
                            <NotNullOrEmptyValidationRule />
                        </Binding.ValidationRules>
                    </Binding>
                </TextBox.Text>


            </TextBox>

The error comes on the Tag NotNullOrEmptyValidationRule. The XAML syntax checker is not able to resolve the NotNullOrEmptyValidationRule. I have even tried putting the namespace but it does not seem to work.

Ad

Answer

i see your binding on the TextBox is set to a path of 'Text' - is that a field on whatever the datacontext of this textbox is? is the textbox actually getting a value put into it? also, if you put a breakpoint in your validation method, is that ever getting fired?

you may want to lookup how to log failures in binding and review those as well..

Ad
source: stackoverflow.com
Ad