Assembly: PresentationFramework (in PresentationFramework.dll)
When a ValidationRule is added to a BindingGroup, the BindingGroup is passed in as the first parameter of the Validate method. You can get the proposed values of the object by using the TryGetValue or GetValue(Object, String) method. You can get the objects that are the sources of the bindings from the Items property.
The following example shows the ValidateDateAndPrice class. The Validate method uses the BindingGroup to get the values the user entered into the form, and checks that if an item is over 100 dollars, it will be available for at least seven days.
Public Class ValidateDateAndPrice Inherits ValidationRule ' Ensure that an item over $100 is available for at least 7 days. Public Overrides Function Validate(ByVal value As Object, ByVal cultureInfo As CultureInfo) As ValidationResult Dim bg As BindingGroup = TryCast(value, BindingGroup) ' Get the source object. Dim item As PurchaseItem = TryCast(bg.Items(0), PurchaseItem) Dim doubleValue As Object = Nothing Dim dateTimeValue As Object = Nothing ' Get the proposed values for Price and OfferExpires. Dim priceResult As Boolean = bg.TryGetValue(item, "Price", doubleValue) Dim dateResult As Boolean = bg.TryGetValue(item, "OfferExpires", dateTimeValue) If (Not priceResult) OrElse (Not dateResult) Then Return New ValidationResult(False, "Properties not found") End If Dim price As Double = CDbl(doubleValue) Dim offerExpires As Date = CDate(dateTimeValue) ' Check that an item over $100 is available for at least 7 days. If price > 100 Then If offerExpires < Date.Today + New TimeSpan(7, 0, 0, 0) Then Return New ValidationResult(False, "Items over $100 must be available for at least 7 days.") End If End If Return ValidationResult.ValidResult End Function End Class