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Cell Validation

  • 4 minutes to read

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

DevExpress WPF | Grid Control - Cell Validation MVVM

View Example: How to Validate 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 below shows how to use the GridViewBase.ValidateCellCommand property to validate cell values:

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

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:

[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.";
}

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:

DevExpress WPF | Grid Control - Cell Validation Error

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:

[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);
}