Cell Validation

Dec 24, 2024
4 minutes to read

The GridControl allows you to validate cell values. The image below shows a GridControl with an invalid cell value:

View Example: How to Validate Cell Editors

Note

When you use a custom CellTemplate, input validation is supported only if the template contains a BaseEdit class descendant declared as demonstrated in the following topic: Custom In-Place Cell Editors.

Initialize a Validation Command

The GridControl contains the following API members that allow you to validate cell values:

API	Description
GridViewBase.ValidateCellCommand / TreeListView.ValidateCellCommand	Gets or sets a command that allows you to validate the focused cell’s data.
GridViewBase.ValidateCell / TreeListView.ValidateCell	Allows you to validate the focused cell’s data.
GridColumn.Validate / TreeListColumn.Validate	Allows you to validate the focused cell’s data in the current column.

The GridControl does not raise these events / execute commands when you change cell values in code. To allow the control to validate these changes, set the DataViewBase.AllowLeaveInvalidEditor property to true.

The code sample (MVVM style) below uses the GridViewBase.ValidateCellCommand property to validate cell values:

XAML

xaml

<dxg:GridControl ItemsSource="{Binding ProductList}">
    <dxg:GridControl.Columns>
        <dxg:GridColumn FieldName="ProductName"/>
        <dxg:GridColumn FieldName="UnitPrice"/>
        <dxg:GridColumn FieldName="Discontinued"/>
    </dxg:GridControl.Columns>
    <dxg:GridControl.View>
        <dxg:TableView ValidateCellCommand="{Binding ValidateCellCommand}"/>
    </dxg:GridControl.View>
</dxg:GridControl>

C#
VB.NET

csharp

using DevExpress.Mvvm;
using DevExpress.Mvvm.DataAnnotations;
using DevExpress.Mvvm.Xpf;
// ...
public class MainViewModel : ViewModelBase {
    // ...
    [Command]
    public void ValidateCell(RowCellValidationArgs args) { }
}

Imports DevExpress.Mvvm
Imports DevExpress.Mvvm.DataAnnotations
Imports DevExpress.Mvvm.Xpf
' ...
Public Class MainViewModel
    Inherits ViewModelBase
    ' ...
    <Command>
    Public Sub ValidateCell(ByVal args As RowCellValidationArgs)

    End Sub
End Class

Validate a New Value

Use the following RowCellValidationArgs properties to get cell values:

The NewValue property returns a cell’s new value.
The OldValue property returns an original value.

To indicate that the new value is invalid, set the Result property to an error description.

In the following code sample, users cannot reduce the product’s price by more than 30% if the product is on discount:

C#
VB.NET

csharp

[Command]
public void ValidateCell(RowCellValidationArgs args) {
    if(args.FieldName != nameof(Product.UnitPrice) || !((Product)args.Item).Discontinued)
        return;
    var cellValue = (double)args.OldValue;
    var discount = 100 - Convert.ToDouble(args.NewValue) / cellValue * 100;
    if(discount > 0 && discount <= 30)
        return;
    args.Result = "Please correct the price.";
}

<Command>
Public Sub ValidateCell(ByVal args As RowCellValidationArgs)
    If args.FieldName <> NameOf(Product.UnitPrice) OrElse Not DirectCast(args.Item, Product).Discontinued Then
        Return
    End If
    Dim cellValue = DirectCast(args.OldValue, Double)
    Dim discount = 100 - Convert.ToDouble(args.NewValue) / cellValue * 100
    If discount > 0 AndAlso discount <= 30 Then
        Return
    End If
    args.Result = "Please correct the price."
End Sub

Indicate Errors

The GridControl displays an error icon within the cell if an edited cell’s value is invalid. Hover the mouse pointer over the error icon to display a tooltip with an error description:

The GridControl does not allow users to close an editor that did not pass validation. Set the DataViewBase.AllowLeaveInvalidEditor property to true to disable this behavior.

Use the Result property to define the error’s icon and description. This property accepts objects of the ValidationErrorInfo type that allows you to specify an error type and content.

If you assign an error description string to the Result property, it casts this string to a ValidationErrorInfo object with the default error icon.

The code sample below demonstrates how to show an error tooltip based on the entered value:

C#
VB.NET

[Command]
public void ValidateCell(RowCellValidationArgs args) {
    if(args.FieldName != nameof(Product.UnitPrice) || !((Product)args.Item).Discontinued)
        return;
    var cellValue = (double)args.OldValue;
    var discount = 100 - Convert.ToDouble(args.NewValue) / cellValue * 100;
    if(discount > 0 && discount <= 30)
        return;

    var error = discount < 0
        ? $"The price cannot be greater than {cellValue}"
        : $"The discount cannot be greater than 30% ({cellValue * 0.7}). Please correct the price.";
    args.Result = new ValidationErrorInfo(error, ValidationErrorType.Critical);
}

<Command>
Public Sub ValidateCell(ByVal args As RowCellValidationArgs)
    If Not Equals(args.FieldName, NameOf(Product.UnitPrice)) OrElse Not CType(args.Item, Product).Discontinued Then Return
    Dim cellValue = CDbl(args.OldValue)
    Dim discount = 100 - Convert.ToDouble(args.NewValue) / cellValue * 100
    If discount > 0 AndAlso discount <= 30 Then Return
    Dim [error] = If(discount < 0, $"The price cannot be greater than {cellValue}", $"The discount cannot be greater than 30% ({cellValue * 0.7}). Please correct the price.")
    args.Result = New ValidationErrorInfo([error], ValidationErrorType.Critical)
End Sub