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2.9 Custom UI validations

The generated UI data objects for our application already provide validation of individual properties, such as when the field is required or when the supplied value was not in the correct format. However, you may need additional UI validations, including cross-field validations.

Let's add a validation to our customized SalesOrderCriteria class, that will check that the From date is not later than the To date for the Order Date criteria, and will add a validation error otherwise.

Adding message resources​

In order to make the text of the validation message localizable, we are going to add it to the Resources.resx file in the AdventureWorks.Client.Common project, and give it a short name OrderFromToDate and the default message text, as follows.

NameValue
OrderFromToDateFrom Order Date should be earlier than To Order Date.

Here is how it will look in Visual Studio.

Resources

Generating message constants​

Along with the resources files, the Xomega template for this project included a T4 Text Template transformation script Messages.tt, which generates Messages.cs file with the resource manager for these resources, as well as constants for message keys that you can use instead of the hardcoded names.

To regenerate the Messages.cs file you need to run the Messages.tt generator after adding your message resources, as shown below.

T4 generator

Adding custom UI validation​

Finally, let's open the SalesOrderCriteriaCustomized.cs file, and override the Validate function on the customized criteria object, where we check the From and To values for the Order Date criteria, and add a validation error, if the former is greater than the latter, as follows.

SalesOrderCriteriaCustomized.cs
public class SalesOrderCriteriaCustomized : SalesOrderCriteria
{
    ...
    public override void Validate(bool force)
    {
        base.Validate(force);
        DateTime? orderDateFrom = OrderDateProperty.Value;
        DateTime? orderDateTo = OrderDate2Property.Value;
        if (orderDateFrom != null && orderDateTo != null && orderDateFrom > orderDateTo)
            validationErrorList.AddValidationError(Messages.OrderFromToDate);
    }
}

Notice how we used the generated constant Messages.OrderFromToDate for our message instead of hardcoding the message key.

Reviewing the results​

Now if you run the application and specify invalid From and To order dates in the criteria and hit Search, you will see our validation error displayed.

Validation results

note

Note that so far we have been adding all that custom code to the generated data objects, which are reusable between multiple C#-based clients, such as Blazor, WPF, or Web Forms.

This means that all these custom validations, cascading selections, etc. will be also available in the corresponding Web Forms or WPF desktop applications out of the box. This is just an example of how Xomega Framework helps you write reusable code.