Validating Data

Xceed DataGrid for WPF offers data validation support at various levels, including cells, row, and business-objects. How and when data is validated is determined by binding- and UI-level validation rules, which are queried when a cell or row is about to end its edit process, when a cell's content is changed, or when data is loaded into a grid.

Binding-level Validation

Through a column's DisplayMemberBindingInfo property, information about a column's binding to its corresponding field in the underlying data source can be defined. In addition, the validation rules to apply to the data as it is read from and written to the data source (e.g., ExceptionValidationRule and DataErrorValidationRule) can be provided by adding the desired validation rules to the ValidationRules collection (see Example 1).

Built-in support for IDataErrorInfo provides business-object level validation that can be used in combination with validation rules.

note

Unless the ValidationRules collection is cleared, it will always contain an ExceptionValidationRule and DataErrorValidationRule. If the DataErrorValidationRule is excluded from the collection of validation rules, validation errors reported by IDataErrorInfo will be ignored.

caution

The ValidationRules collection cannot be cleared once the binding has been established.

The moment when the data is written to the underlying data source, and therefore validated, is determined by the value of a grid's UpdateSourceTrigger property, which indicates whether the source is updated when a cell or row is ending its edit process or when a cell's content is changed.

UI-level Validation

Through the use of cell validation rules, the content of any cell can be validated before it is committed to the underlying data source. These rules can be provided for all the cells in a column by adding one or more CellValidationRule objects to a CellValidationRules collection or on a per-cell basis (see Example 2).

Validation Errors

When the value of a cell fails the validation process, its HasValidationError property will return true, and its ValidationError property will contain a CellValidationError, which provides information on the cell in error, the error content, the exception (if one was thrown), and the validation rule that failed. If the validation rule that failed is a binding-level ValidationRule, it will be wrapped in a PassthroughCellValidationRule.Validation errors will also be reported by a row when the value of one or more of its cells fail the validation process. Like cells, when a row contains validation errors, its HasValidationError property will return true, and its ValidationError property will contain a RowValidationError, which provides information on the row in error, the error content, the exception, and the validation rule that failed.

The IsValidationErrorRestrictive property indicates whether the validation error that failed prevents the focus from moving to another row until the error is fixed. Usually, all errors are restrictive; however, validation errors reported through IDataErrorInfo are considered non-restrictive.

tip

Any validation rule created from the ValidationRule class can be reused in a grid by using a PassthroughCellValidationRule, which wraps any validation rule and exposes it as a CellValidationRule.

Validation Order and Chained Validations

Data is validated first by UI-level validation rules when data is modified, followed by the binding-level rules when the modified data is written back to the source.

When a cell is successfully validated, an attempt will be made to re-validate any sibling cells that have validation errors. If more than one sibling cell has validation errors, their data will be re-validated at the same time. If, once the sibling cells have been successfully validated, other siblings have validation errors, they will be re-validated and so forth.

Examples

All examples in this topic assume that the grid is bound to a list of Composer objects, unless stated otherwise.

Example 1: Providing binding-level validation

The following example demonstrates how to create a custom ValidationRule and apply it to a column's binding to provide binding-level validation.

The implementation for the YearValidationRule is provided below.

XAML

  <Grid xmlns:xcdg="http://schemas.xceed.com/wpf/xaml/datagrid"
      xmlns:local="clr-namespace:Xceed.Wpf.Documentation">
    <Grid.Resources>
      <xcdg:DataGridCollectionViewSource x:Key="cvs_composers"
                                          Source="{Binding Source={x:Static Application.Current}, 
                                                          Path=Composers}"/>
    </Grid.Resources>
  
    <xcdg:DataGridControl ItemsSource="{Binding Source={StaticResource cvs_composers}}"
                          UpdateSourceTrigger="RowEndingEdit">
      <xcdg:DataGridControl.Columns> 
        <xcdg:Column FieldName="BirthYear">
            <xcdg:Column.DisplayMemberBindingInfo>
              <xcdg:DataGridBindingInfo Path="BirthYear">
                  <xcdg:DataGridBindingInfo.ValidationRules>
                    <local:YearValidationRule />
                  </xcdg:DataGridBindingInfo.ValidationRules>
              </xcdg:DataGridBindingInfo>
            </xcdg:Column.DisplayMemberBindingInfo>
        </xcdg:Column>
        <xcdg:Column FieldName="DeathYear">
            <xcdg:Column.DisplayMemberBindingInfo>
              <xcdg:DataGridBindingInfo Path="DeathYear">
                  <xcdg:DataGridBindingInfo.ValidationRules>
                    <local:YearValidationRule />
                  </xcdg:DataGridBindingInfo.ValidationRules>
              </xcdg:DataGridBindingInfo>
            </xcdg:Column.DisplayMemberBindingInfo>
        </xcdg:Column>      
      </xcdg:DataGridControl.Columns>
    </xcdg:DataGridControl>
  </Grid>

C#

using System;
using System.Windows.Controls;
using System.Globalization;
namespace Xceed.Wpf.Documentation
{
  public class YearValidationRule : ValidationRule
  {
    public override ValidationResult Validate( object value, CultureInfo cultureInfo )
    {
      int year = ( int )value;
      if( year > DateTime.Now.Year )
        return new ValidationResult( false, "Chosen year cannot be greater than this year." );
      return ValidationResult.ValidResult;
    }
  }
}

VB.NET

Imports System
Imports System.Windows.Controls
Imports System.Globalization
Namespace Xceed.Wpf.Documentation
  Public Class YearValidationRule
              Inherits ValidationRule
    Public Overrides Function Validate( ByVal value As Object, _
                                        ByVal cultureInfo As CultureInfo ) As ValidationResult
      Dim year As Integer = CInt( value )
      If year > DateTime.Now.Year Then
        Return New ValidationResult( False, "Chosen year cannot be greater than this year." )
      End If
      Return ValidationResult.ValidResult
    End Function
  End Class
End Namespace

Example 2: Providing UI-level validation

The following example demonstrates how to create a custom CellValidationRule and add it to a column's CellValidationRules collection to provide UI-level validation.

The implementation for the PeriodVSCompositionCountCellValidationRule and Person class are provided below.

XAML

<Grid xmlns:xcdg="http://schemas.xceed.com/wpf/xaml/datagrid"
      xmlns:local="clr-namespace:Xceed.Wpf.Documentation">
  <Grid.Resources>
    <xcdg:DataGridCollectionViewSource x:Key="cvs_composers"
                                        Source="{Binding Source={x:Static Application.Current},
                                                        Path=Composers}"/>
    <!--A data provider to bind to the Period enum-->
    <ObjectDataProvider x:Key="periods"
                        MethodName="GetValues"
                        ObjectType="{x:Type local:Period}">
        <ObjectDataProvider.MethodParameters>
          <x:Type TypeName="local:Period"/>
        </ObjectDataProvider.MethodParameters>
    </ObjectDataProvider>
    <!--A cell editor that will be used to edit a Period column with a combo box-->
    <xcdg:CellEditor x:Key="periodEditor">
        <xcdg:CellEditor.EditTemplate>
          <DataTemplate>
              <ComboBox BorderThickness="0"
                        MinHeight="22"
                        VerticalContentAlignment="Top"
                        SelectedValuePath="."
                        ItemsSource="{Binding Source={StaticResource periods}}"
                        SelectedValue="{xcdg:CellEditorBinding}">
                <ComboBox.Resources>
                    <Style TargetType="Popup">
                      <Setter Property="TextElement.Foreground"
                              Value="{DynamicResource {x:Static SystemColors.WindowTextBrushKey}}" />
                    </Style>
                </ComboBox.Resources>
              </ComboBox>
          </DataTemplate>
        </xcdg:CellEditor.EditTemplate>
    </xcdg:CellEditor>
  </Grid.Resources>
  <xcdg:DataGridControl ItemsSource="{Binding Source={StaticResource cvs_composers}}"
                        UpdateSourceTrigger="RowEndingEdit">
    <xcdg:DataGridControl.Columns>
      <xcdg:Column FieldName="Period"
                    CellEditor="{StaticResource periodEditor}">                                   
          <xcdg:Column.CellValidationRules>
            <local:PeriodVSCompositionCountCellValidationRule/>
          </xcdg:Column.CellValidationRules>
      </xcdg:Column>
      <xcdg:Column FieldName="CompositionCount">
          <xcdg:Column.CellValidationRules>
            <local:PeriodVSCompositionCountCellValidationRule />
          </xcdg:Column.CellValidationRules>
      </xcdg:Column>
    </xcdg:DataGridControl.Columns>
  </xcdg:DataGridControl>
</Grid>

C#

  using System;
  using Xceed.Wpf.DataGrid.ValidationRules;
  using Xceed.Wpf.DataGrid;
  using System.Globalization;
  using System.Windows.Controls;
  namespace Xceed.Wpf.Documentation
  { 
    public class PeriodVSCompositionCountCellValidationRule : CellValidationRule
    {
      public override ValidationResult Validate( object value, CultureInfo culture,
                                                  CellValidationContext context )
      {
        Row parentRow = context.Cell.ParentRow;
        int compositionCount;
        Period period;
        if( context.Cell.FieldName == "Period" )
        {
          period = ( Period )value;       
          compositionCount = ( int )parentRow.Cells[ "CompositionCount" ].Content;
        }
        else
        {
          period = ( Period )parentRow.Cells[ "Period" ].Content;
          compositionCount = ( int )value;
        }
        if( ( period == Period.Modern ) && compositionCount > 40 )
          return new ValidationResult( false, "Composition count must be less than 50 when the period is set to Modern." );
        return ValidationResult.ValidResult;
      }
    }
  }
  /*...*/
  using System.ComponentModel;
  using System.Windows.Media;
  namespace Xceed.Wpf.Documentation
  {
    public class Person: INotifyPropertyChanged, IDataErrorInfo
    {
      public Person( int personID, string firstName, string lastName, int age )
      {
        m_personID = personID;
        m_firstName = firstName;
        m_lastName = lastName;
        m_age = age;
      }
      public Person()
      {
      }
      public int PersonID
      {
        get
        {
          return m_personID;
        }
      }
      public string FirstName
      {
        get
        {
          return m_firstName;
        }
        set
        {
          if( m_firstName != value )
          {
            m_firstName = value;
            this.OnPropertyChanged( "FirstName" );
          }
        }
      }
      public string LastName
      {
        get
        {
          return m_lastName;
        }
        set
        {
          if( m_lastName != value )
          {
            m_lastName = value;
            this.OnPropertyChanged( "LastName" );
          }
        }
      }
      public int Age
      {
        get
        {
          return m_age;
        }
        set
        {
          if( m_age == value )
            return;
          m_age = value;
          this.OnPropertyChanged( "Age" );
        }
      }
      // INotifyPropertyChanged implementation
      public event PropertyChangedEventHandler PropertyChanged;
      private void OnPropertyChanged( string propertyName )
      {
        if( this.PropertyChanged != null )
          this.PropertyChanged( this, new PropertyChangedEventArgs( propertyName ) );
      }
      // IDataErrorInfo implementation
      [EditorBrowsable( EditorBrowsableState.Never ) ]
      [Browsable( false )]
      public string Error
      {
        get
        {
          return "IDataErrorInfo Error Message";
        }
      }
      [EditorBrowsable( EditorBrowsableState.Never )]
      [Browsable( false )]
      public string this[ string propertyName ]
      {
        get
        {
          if( propertyName == "Age" )
          {
            if( m_age < 18 )
              return "An employee must be 18 years or older.";
          }
          return string.Empty;
        }
      }   
      private string m_firstName = string.Empty;
      private string m_lastName = string.Empty;
      private int m_personID;
      private int m_age = 18;
    }
  }

VB.NET

  Imports System
  Imports Xceed.Wpf.DataGrid.ValidationRules
  Imports Xceed.Wpf.DataGrid
  Imports System.Globalization
  Imports System.Windows.Controls
  Namespace Xceed.Wpf.Documentation
    Public Class PeriodVSCompositionCountCellValidationRule
                Inherits CellValidationRule
      Public Overrides Function Validate( ByVal value As Object, ByVal culture As CultureInfo, _
                                          ByVal context As CellValidationContext ) As ValidationResult
        Dim parentRow As Row = context.Cell.ParentRow
        Dim compositionCount As Integer
        Dim period As Period
        If context.Cell.FieldName = "Period" Then
          period = CType( value, Period )
          compositionCount = CInt( parentRow.Cells( "CompositionCount" ).Content )
        Else
          period = CType( parentRow.Cells( "Period" ).Content, Period )
          compositionCount = CInt( value )
        End If
        If( ( period = Period.Modern ) And ( compositionCount > 40 ) ) Then
          Return New ValidationResult( False, "Composition count must be less than 50 when the period is set to Modern." );
        End If
        Return ValidationResult.ValidResult
      End Function
    End Class
  End Namespace
  '...
  Imports System.ComponentModel
  Imports System.Windows.Media
  Namespace Xceed.Wpf.Documentation
    Public Class Person
                Implements INotifyPropertyChanged
      Public Sub New( personID As Integer, firstName As String, lastName As String, age As Integer )
        m_personID = personID
        m_firstName = firstName
        m_lastName = lastName
        m_age = age
      End Sub
      public Sub New()
      End sub   
      Public ReadOnly Property PersonID As Integer
        Get
          Return m_personID
        End Get
      End Property
      Public Property FirstName As String
        Get
          Return m_firstName
        End Get
        Set( ByVal value As String )
          If m_firstName <> value Then
            m_firstName = value
            Me.OnPropertyChanged( "FirstName" )
          End If
        End Set
      End Property
      Public Property LastName As String
        Get
          Return m_lastName
        End Get
        Set( ByVal value As String )
          If m_lastName <> value Then
            m_lastName = value
            Me.OnPropertyChanged( "LastName" )
          End If
        End Set
      End Property
      Public Property Age As Integer
        Get
          Return m_age
        End Get
        Set( ByVal value As Integer )
          If m_age = value Then
            Return
          End If
          m_age = value
          Me.OnPropertyChanged( "Age" )
        End Set
      End Property
      ' INotifyPropertyChanged implementation
      Public Event PropertyChanged As PropertyChangedEventHandler Implements INotifyPropertyChanged.PropertyChanged
      Private Sub OnPropertyChanged( ByVal propertyName As String )
        If Not Me.PropertyChanged Is Nothing Then
          Me.PropertyChanged( Me, New PropertyChangedEventArgs( propertyName ) )
        End If
      End Sub
      private string m_firstName = string.Empty;
      private string m_lastName = string.Empty;
      private m_personID As Integer
      Private m_age As Integer = 18
    End Class
  End Namespace