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How to: Implement Validation with the DataGrid Control

The DataGrid control enables you to perform validation at both the cell and row level. With cell-level validation, you validate individual properties of a bound data object when a user updates a value. With row-level validation, you validate entire data objects when a user commits changes to a row. You can also provide customized visual feedback for validation errors, or use the default visual feedback that the DataGrid control provides.

The following procedures describe how to apply validation rules to DataGrid bindings and customize the visual feedback.

To validate individual cell values

  • Specify one or more validation rules on the binding used with a column. This is similar to validating data in simple controls, as described in Data Binding Overview.

    The following example shows a DataGrid control with four columns bound to different properties of a business object. Three of the columns specify the ExceptionValidationRule by setting the ValidatesOnExceptions property to true.

    
    <Grid>
    
      <Grid.Resources>
        <local:Courses x:Key="courses"/>
      </Grid.Resources>
    
      <DataGrid Name="dataGrid1" FontSize="20"
        ItemsSource="{StaticResource courses}" 
        AutoGenerateColumns="False">
        <DataGrid.Columns>
          <DataGridTextColumn Header="Course Name" 
            Binding="{Binding Name, TargetNullValue=(enter a course name)}"/>
          <DataGridTextColumn Header="Course ID"
            Binding="{Binding Id, ValidatesOnExceptions=True}"/>
          <DataGridTextColumn Header="Start Date"
            Binding="{Binding StartDate, ValidatesOnExceptions=True, 
              StringFormat=d}"/>
          <DataGridTextColumn Header="End Date"
            Binding="{Binding EndDate, ValidatesOnExceptions=True,
              StringFormat=d}"/>
        </DataGrid.Columns>
      </DataGrid>
    
    </Grid>
    
    
    

    When a user enters an invalid value (such as a non-integer in the Course ID column), a red border appears around the cell. You can change this default validation feedback as described in the following procedure.

To customize cell validation feedback

  • Set the column's EditingElementStyle property to a style appropriate for the column's editing control. Because the editing controls are created at run time, you cannot use the Validation.ErrorTemplate attached property like you would with simple controls.

    The following example updates the previous example by adding an error style shared by the three columns with validation rules. When a user enters an invalid value, the style changes the cell background color and adds a ToolTip. Note the use of a trigger to determine whether there is a validation error. This is required because there is currently no dedicated error template for cells.

    
    <DataGrid.Resources>
      <Style x:Key="errorStyle" TargetType="{x:Type TextBox}">
        <Setter Property="Padding" Value="-2"/>
        <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>
    </DataGrid.Resources>
    
    <DataGrid.Columns>
      <DataGridTextColumn Header="Course Name" 
        Binding="{Binding Name, TargetNullValue=(enter a course name)}"/>
      <DataGridTextColumn Header="Course ID"
        EditingElementStyle="{StaticResource errorStyle}"
        Binding="{Binding Id, ValidatesOnExceptions=True}"/>
      <DataGridTextColumn Header="Start Date"
        EditingElementStyle="{StaticResource errorStyle}"
        Binding="{Binding StartDate, ValidatesOnExceptions=True, 
          StringFormat=d}"/>
      <DataGridTextColumn Header="End Date"
        EditingElementStyle="{StaticResource errorStyle}"
        Binding="{Binding EndDate, ValidatesOnExceptions=True,
          StringFormat=d}"/>
    </DataGrid.Columns>
    
    
    

    You can implement more extensive customization by replacing the CellStyle used by the column.

To validate multiple values in a single row

  1. Implement a ValidationRule subclass that checks multiple properties of the bound data object. In your Validate method implementation, cast the value parameter value to a BindingGroup instance. You can then access the data object through the Items property.

    The following example demonstrates this process to validate whether the StartDate property value for a Course object is earlier than its EndDate property value.

    
    public class CourseValidationRule : ValidationRule
    {
        public override ValidationResult Validate(object value,
            System.Globalization.CultureInfo cultureInfo)
        {
            Course course = (value as BindingGroup).Items[0] as Course;
            if (course.StartDate > course.EndDate)
            {
                return new ValidationResult(false,
                    "Start Date must be earlier than End Date.");
            }
            else
            {
                return ValidationResult.ValidResult;
            }
        }
    }
    
    
    
  2. Add the validation rule to the DataGrid.RowValidationRules collection. The RowValidationRules property provides direct access to the ValidationRules property of a BindingGroup instance that groups all the bindings used by the control.

    The following example sets the RowValidationRules property in XAML. The ValidationStep property is set to UpdatedValue so that the validation occurs only after the bound data object is updated.

    
    <DataGrid.RowValidationRules>
      <local:CourseValidationRule ValidationStep="UpdatedValue"/>
    </DataGrid.RowValidationRules>
    
    
    

    When a user specifies an end date that is earlier than the start date, a red exclamation mark (!) appears in the row header. You can change this default validation feedback as described in the following procedure.

To customize row validation feedback

  • Set the DataGrid.RowValidationErrorTemplate property. This property enables you to customize row validation feedback for individual DataGrid controls. You can also affect multiple controls by using an implicit row style to set the DataGridRow.ValidationErrorTemplate property.

    The following example replaces the default row validation feedback with a more visible indicator. When a user enters an invalid value, a red circle with a white exclamation mark appears in the row header. This occurs for both row and cell validation errors. The associated error message is displayed in a ToolTip.

    
    <DataGrid.RowValidationErrorTemplate>
      <ControlTemplate>
        <Grid Margin="0,-2,0,-2"
          ToolTip="{Binding RelativeSource={RelativeSource
          FindAncestor, AncestorType={x:Type DataGridRow}},
          Path=(Validation.Errors)[0].ErrorContent}">
          <Ellipse StrokeThickness="0" Fill="Red" 
            Width="{TemplateBinding FontSize}" 
            Height="{TemplateBinding FontSize}" />
          <TextBlock Text="!" FontSize="{TemplateBinding FontSize}" 
            FontWeight="Bold" Foreground="White" 
            HorizontalAlignment="Center"  />
        </Grid>
      </ControlTemplate>
    </DataGrid.RowValidationErrorTemplate>
    
    
    

The following example provides a complete demonstration for cell and row validation. The Course class provides a sample data object that implements IEditableObject to support transactions. The DataGrid control interacts with IEditableObject to enable users to revert changes by pressing ESC.

NoteNote

If you are using Visual Basic, in the first line of MainWindow.xaml, replace x:Class="DataGridValidation.MainWindow" with x:Class="MainWindow".

To test the validation, try the following:

  • In the Course ID column, enter a non-integer value.

  • In the End Date column, enter a date that is earlier than the Start Date.

  • Delete the value in Course ID, Start Date, or End Date.

  • To undo an invalid cell value, put the cursor back in the cell and press the ESC key.

  • To undo changes for an entire row when the current cell is in edit mode, press the ESC key twice.

  • When a validation error occurs, move your mouse pointer over the indicator in the row header to see the associated error message.


using System;
using System.Collections.ObjectModel;
using System.ComponentModel;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;

namespace DataGridValidation
{
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
            dataGrid1.InitializingNewItem += (sender, e) =>
            {
                Course newCourse = e.NewItem as Course;
                newCourse.StartDate = newCourse.EndDate = DateTime.Today;
            };
        }
    }

    public class Courses : ObservableCollection<Course>
    {
        public Courses()
        {
            this.Add(new Course
            {
                Name = "Learning WPF",
                Id = 1001,
                StartDate = new DateTime(2010, 1, 11),
                EndDate = new DateTime(2010, 1, 22)
            });
            this.Add(new Course
            {
                Name = "Learning Silverlight",
                Id = 1002,
                StartDate = new DateTime(2010, 1, 25),
                EndDate = new DateTime(2010, 2, 5)
            });
            this.Add(new Course
            {
                Name = "Learning Expression Blend",
                Id = 1003,
                StartDate = new DateTime(2010, 2, 8),
                EndDate = new DateTime(2010, 2, 19)
            });
            this.Add(new Course
            {
                Name = "Learning LINQ",
                Id = 1004,
                StartDate = new DateTime(2010, 2, 22),
                EndDate = new DateTime(2010, 3, 5)
            });
        }
    }

    public class Course : IEditableObject, INotifyPropertyChanged
    {
        private string _name;
        public string Name
        {
            get
            {
                return _name;
            }
            set
            {
                if (_name == value) return;
                _name = value;
                OnPropertyChanged("Name");
            }
        }

        private int _number;
        public int Id
        {
            get
            {
                return _number;
            }
            set
            {
                if (_number == value) return;
                _number = value;
                OnPropertyChanged("Id");
            }
        }

        private DateTime _startDate;
        public DateTime StartDate
        {
            get
            {
                return _startDate;
            }
            set
            {
                if (_startDate == value) return;
                _startDate = value;
                OnPropertyChanged("StartDate");
            }
        }

        private DateTime _endDate;
        public DateTime EndDate
        {
            get
            {
                return _endDate;
            }
            set
            {
                if (_endDate == value) return;
                _endDate = value;
                OnPropertyChanged("EndDate");
            }
        }

        #region IEditableObject

        private Course backupCopy;
        private bool inEdit;

        public void BeginEdit()
        {
            if (inEdit) return;
            inEdit = true;
            backupCopy = this.MemberwiseClone() as Course;
        }

        public void CancelEdit()
        {
            if (!inEdit) return;
            inEdit = false;
            this.Name = backupCopy.Name;
            this.Id = backupCopy.Id;
            this.StartDate = backupCopy.StartDate;
            this.EndDate = backupCopy.EndDate;
        }

        public void EndEdit()
        {
            if (!inEdit) return;
            inEdit = false;
            backupCopy = null;
        }

        #endregion

        #region INotifyPropertyChanged

        public event PropertyChangedEventHandler PropertyChanged;

        private void OnPropertyChanged(string propertyName)
        {
            if (PropertyChanged != null)
            {
                PropertyChanged(this,
                    new PropertyChangedEventArgs(propertyName));
            }
        }

        #endregion

    }

    public class CourseValidationRule : ValidationRule
    {
        public override ValidationResult Validate(object value,
            System.Globalization.CultureInfo cultureInfo)
        {
            Course course = (value as BindingGroup).Items[0] as Course;
            if (course.StartDate > course.EndDate)
            {
                return new ValidationResult(false,
                    "Start Date must be earlier than End Date.");
            }
            else
            {
                return ValidationResult.ValidResult;
            }
        }
    }

}



<Window x:Class="DataGridValidation.MainWindow"
  xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
  xmlns:local="clr-namespace:DataGridValidation"
  Title="DataGrid Validation Example" Height="240" Width="600">

  <Grid>

    <Grid.Resources>
      <local:Courses x:Key="courses"/>
    </Grid.Resources>

    <DataGrid Name="dataGrid1" FontSize="20" RowHeaderWidth="27"
      ItemsSource="{StaticResource courses}" 
      AutoGenerateColumns="False">

      <DataGrid.Resources>
        <Style x:Key="errorStyle" TargetType="{x:Type TextBox}">
          <Setter Property="Padding" Value="-2"/>
          <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>
      </DataGrid.Resources>

      <DataGrid.Columns>
        <DataGridTextColumn Header="Course Name" 
          Binding="{Binding Name, TargetNullValue=(enter a course name)}"/>
        <DataGridTextColumn Header="Course ID"
          EditingElementStyle="{StaticResource errorStyle}"
          Binding="{Binding Id, ValidatesOnExceptions=True}"/>
        <DataGridTextColumn Header="Start Date"
          EditingElementStyle="{StaticResource errorStyle}"
          Binding="{Binding StartDate, ValidatesOnExceptions=True, 
            StringFormat=d}"/>
        <DataGridTextColumn Header="End Date"
          EditingElementStyle="{StaticResource errorStyle}"
          Binding="{Binding EndDate, ValidatesOnExceptions=True,
            StringFormat=d}"/>
      </DataGrid.Columns>

      <DataGrid.RowValidationRules>
        <local:CourseValidationRule ValidationStep="UpdatedValue"/>
      </DataGrid.RowValidationRules>

      <DataGrid.RowValidationErrorTemplate>
        <ControlTemplate>
          <Grid Margin="0,-2,0,-2"
            ToolTip="{Binding RelativeSource={RelativeSource
            FindAncestor, AncestorType={x:Type DataGridRow}},
            Path=(Validation.Errors)[0].ErrorContent}">
            <Ellipse StrokeThickness="0" Fill="Red" 
              Width="{TemplateBinding FontSize}" 
              Height="{TemplateBinding FontSize}" />
            <TextBlock Text="!" FontSize="{TemplateBinding FontSize}" 
              FontWeight="Bold" Foreground="White" 
              HorizontalAlignment="Center"  />
          </Grid>
        </ControlTemplate>
      </DataGrid.RowValidationErrorTemplate>

    </DataGrid>

  </Grid>
</Window>


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