IDataErrorInfo Interface
[ This article is for Windows Phone 8 developers. If you’re developing for Windows 10, see the latest documentation. ]
Defines members that data entity classes can implement to provide custom validation support.
Assembly: System.Windows (in System.Windows.dll)
The IDataErrorInfo type exposes the following members.
This interface enables data entity classes to implement custom validation rules and expose validation results to the user interface. You typically implement this interface to provide relatively simple validation logic.
To provide asynchronous or server-side validation logic, implement the INotifyDataErrorInfo interface instead.
In general, new entity classes should implement INotifyDataErrorInfo for the added flexibility instead of implementing IDataErrorInfo. The IDataErrorInfo support enables you to use many existing entity classes that are written for the full .NET Framework. Other validation options are also available, such as the use of data attributes. For more information, see Data binding for Windows Phone 8.
IDataErrorInfo Members
The IDataErrorInfo::Item property returns a single validation error message. The Error property returns a single error message for the entire object. Each of these single messages can represent multiple errors. If you want to represent multiple errors by using multiple custom error objects, implement the INotifyDataErrorInfo interface instead. This enables more detailed error reporting in the user interface (UI).
Data Binding Support
The XAML binding engine provides built-in support for IDataErrorInfo. To enable this support, bind a control to a property of an entity that implements IDataErrorInfo, and set the Binding::ValidatesOnDataErrors property to true. Then, whenever a bound entity property changes value, the binding engine validates the new value by passing the property name to IDataErrorInfo::Item. Note that the binding engine never uses the Error property, although you can use it in custom error reporting to display object-level errors.
The binding engine uses the validation results to update the Validation::Errors collection for that binding. First, the binding engine removes any existing errors for the bound property that originate from exceptions or from IDataErrorInfo validation. Then, if the new value is not valid, the binding engine adds a new error for the property.
You can use ValidatesOnExceptions and ValidatesOnDataErrors at the same time; however, any exceptions that occur will prevent IDataErrorInfo validation.
Error Reporting
The Validation::Errors collection provides a binding source for error reporting in the user interface. Several controls bind to this collection from their default control templates.
To provide custom error reporting, you can replace the default templates with customized versions. You can also set the Binding::NotifyOnValidationError property to true and handle the FrameworkElement::BindingValidationError event. This event occurs each time an error is added or removed for a particular binding. Some controls require this mechanism instead of using the Validation::Errors collection.
The following example code demonstrates how to implement IDataErrorInfo. This example uses the same error reporting structure as the example for the INotifyDataErrorInfo interface. However, in the IDataErrorInfo implementation, multiple errors for a single property are combined into a single error message. This limits the options for custom error reporting. Additionally, the IDataErrorInfo interface does not support the future addition of asynchronous validation rules.
To test this example, type in different values and change the focus to the other text box. Here are the values that you can test:
Id less than 5.
Id greater than 10.
Name with spaces.
Name with more than 5 characters.
<phone:PhoneApplicationPage x:Class="IDataErrorInfoExample.MainPage" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:phone="clr-namespace:Microsoft.Phone.Controls;assembly=Microsoft.Phone" xmlns:shell="clr-namespace:Microsoft.Phone.Shell;assembly=Microsoft.Phone" xmlns:d="http://schemas.microsoft.com/expression/blend/2008" xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" mc:Ignorable="d" d:DesignHeight="800" d:DesignWidth="480" FontFamily="{StaticResource PhoneFontFamilyNormal}" FontSize="{StaticResource PhoneFontSizeNormal}" Foreground="{StaticResource PhoneForegroundBrush}"> <Grid x:Name="LayoutRoot" Background="Transparent" Margin="10"> <Grid.RowDefinitions> <RowDefinition Height="Auto"/> <RowDefinition Height="Auto"/> <RowDefinition Height="Auto"/> <RowDefinition Height="Auto"/> </Grid.RowDefinitions> <TextBlock Grid.Column="0" Margin="3" Text="Product Id"/> <StackPanel Grid.Row="1" x:Name="IdField" Orientation="Vertical"> <TextBox KeyDown="DataField_KeyDown" Text="{Binding Id, Mode=TwoWay, ValidatesOnDataErrors=True, NotifyOnValidationError=True}" BindingValidationError="OnBindingValidationError" BorderThickness="2" Width="250" HorizontalAlignment="Left"/> <TextBlock Foreground="Red" TextWrapping="Wrap" Width="400" Margin="0,10"/> </StackPanel> <TextBlock Grid.Row="2" Margin="3" Text="Product Name"/> <StackPanel Grid.Row="3" x:Name="NameField" Orientation="Vertical"> <TextBox KeyDown="DataField_KeyDown" Text="{Binding Name, Mode=TwoWay, ValidatesOnDataErrors=True, NotifyOnValidationError=True}" BindingValidationError="OnBindingValidationError" BorderThickness="2" Width="250" HorizontalAlignment="Left"/> <TextBlock Foreground="Red" TextWrapping="Wrap" Width="400" Margin="0,10" /> </StackPanel> </Grid> </phone:PhoneApplicationPage>