How Validation.HasError property is updated for user input validation?

Question

In this tutorial there is a text box that shows a pink background for invalid data. This is the wpf code:

<TextBox Text="{Binding Aid,UpdateSourceTrigger=PropertyChanged,Mode=TwoWay,ValidatesOnDataErrors=True}" 
             Canvas.Left="95" Canvas.Top="60" Width="297">

<TextBox.Style>
            <Style TargetType="TextBox">
                <Style.Triggers>
                    <Trigger  Property="Validation.HasError" Value="True">
                        <Setter Property="Background" Value="Pink"/>
                        ...
                    </Trigger>
                </Style.Triggers>
            </Style>
        </TextBox.Style>

        <Validation.ErrorTemplate>
            <ControlTemplate>                    
                <StackPanel>
                    <AdornedElementPlaceholder x:Name="textBox" ToolTip="{Binding [0].ErrorContent}"/>
                </StackPanel>
            </ControlTemplate>
        </Validation.ErrorTemplate>

    </TextBox>

But I don't get how Validation.HasError is updated as the user inputs the value?

Answer 1

This sample project takes advantage of IDataErrorInfo interface which makes data validation very simple. This link will describe it in details .