Adding INotifyDataErrorInfo Support to the ValidationSummary Control

Now that you have looked at the INotifyDataErrorInfo interface and at the inner workings of the custom validation system, let us examine how the ValidationSummary control has been extended to support the INotifyDataErrorInfo interface.

As you saw in the previous section, the ValidationSummary control monitors its data context for validation errors if the data context implements INotifyDataErrorInfo. When the INotifyDataErrorInfo.ErrorsChanged event is raised by the data context, the control’s HandleErrorsChanged handler is called (see Listing 26.5).

ValidationSummary maintains a dictionary of validation errors, which are keyed by the associated property name. The HandleErrorsChanged method retrieves the list of validation errors from the INotifyDataErrorInfo and combines the list with the list in its own dictionary. If no list exists for the particular property name, a new list is added to the dictionary.

LISTING 26.5. ValidationSummary.HandleErrorsChanged Method

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void HandleErrorsChanged(object sender, DataErrorsChangedEventArgs args)
{
    INotifyDataErrorInfo notifier = sender as INotifyDataErrorInfo;
    if (notifier == null)
    {
        return;
    }

    string propertyName = args.PropertyName;
    if (string.IsNullOrEmpty(propertyName))
    {
        return;
    }

    IEnumerable notifierErrors = notifier.GetErrors(args.PropertyName);

    List<object> errorList;
    if (!errorLookup.TryGetValue(propertyName, out errorList))
    {
        errorList = new List<object>();
    }

    foreach (var error in errorList)
    {
        RemoveError(error);
    }

    errorList.Clear();

    foreach (var error in notifierErrors)
    {
        AddError(error);
    }
    errorLookup[propertyName] = errorList;

    foreach (var error in errorList)
    {
        AddError(error);
    }
}

The ValidationSummary control now has support for both the property setter validation approach and for the Silverlight 4 INotifyDataErrorInfo validation approach.