I've been developing a custom ValidationRule, following the MS example by the letter but it is throwing an ArhumentOutOfRangeException during the validation process.
I have the following ValidationRule
public class MyValidationRule : ValidationRule
{
}
The TextBoxInError style is defined as follows
Validation is performed as expected, and the tooltip is correctly set. However, when the ValidationResult changes, the following error is reported
System.Windows.Data Error: 12 : Cannot get '' value (type 'ValidationError') from '(Validation.Errors)' (type 'ReadOnlyObservableCollection`1'). BindingExpression:Path=(0).[0].ErrorContent; DataItem='MyTextBox' (Name='_myTextBox'); target element is 'MyTextBox' (Name='_myTextBox'); target property is 'ToolTip' (type 'Object') TargetInvocationException:'System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> System.ArgumentOutOfRangeException: Index was out of range. Must be non-negative and less than the size of the collection.
Parameter name: index
at System.ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument argument, ExceptionResource resource)
at System.ThrowHelper.ThrowArgumentOutOfRangeException()
at System.Collections.Generic.List`1.get_Item(Int32 index)
at System.Collections.ObjectModel.Collection`1.get_Item(Int32 index)
at System.Collections.ObjectModel.ReadOnlyCollection`1.get_Item(Int32 index)
--- End of inner exception stack trace ---
at System.RuntimeMethodHandle._InvokeMethodFast(Object target, Object[] arguments, SignatureStruct& sig, MethodAttributes methodAttributes, RuntimeTypeHandle typeOwner)
at System.RuntimeMethodHandle.InvokeMethodFast(Object target, Object[] arguments, Signature sig, MethodAttributes methodAttributes, RuntimeTypeHandle typeOwner)
at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture, Boolean skipVisibilityChecks)
at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
at System.Reflection.RuntimePropertyInfo.GetValue(Object obj, BindingFlags invokeAttr, Binder binder, Object[] index, CultureInfo culture)
at MS.Internal.Data.PropertyPathWorker.GetValue(Object item, Int32 level)
at MS.Internal.Data.PropertyPathWorker.RawValue(Int32 k)'
It seems that accessing ValidationErrors[0] is the cause of the exception, but I cannot see how this is occuring since that property is only accessed when an Error exists.
Any pointers appreciated.