Question

I wish I could be more descriptive in my title, but I am having trouble understanding the exception below.

I had this happen recently, and it turned out to be a DependencyProperty that wasn’t properly declared, but I discovered that without the help of this exception.

The only other thing I can add about it is that it happens when my GetHashCode method is invoked, which triggers a method that derives a hash by reflecting on the object’s public properties. In this case, the object is derived from a ViewModelBase class, and the exception gets hit on a property it calls Item, which I am guessing is the indexor that isw part of IDataErrorInfo, but that’s just a guess here.

All of that said, my gut is that it’s just a bad DataBinding that is being hit before any useful debug information is output.

Any suggestions?

Cheers,
Berryl

System.Reflection.TargetParameterCountException was unhandled by user code
  Message=Parameter count mismatch.
  Source=mscorlib
  StackTrace:
       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, Object[] index)
       at Smack.Core.Lib.DomainSuperTypes.EntityImpl.BaseObject.GetHashCode() in C:\Users\Lord & Master\Documents\Projects\Smack\trunk\src\Core\DomainSuperTypes\EntityImpl\BaseObject.cs:line 51
       at Smack.Core.Lib.DomainSuperTypes.EntityImpl.ValueObject.GetHashCode() in C:\Users\Lord & Master\Documents\Projects\Smack\trunk\src\Core\DomainSuperTypes\EntityImpl\ValueObject.cs:line 68
       at System.Collections.Hashtable.get_Item(Object key)
       at System.ComponentModel.TypeDescriptor.NodeFor(Object instance, Boolean createDelegator)
       at System.ComponentModel.TypeDescriptor.GetDescriptor(Object component, Boolean noCustomTypeDesc)
       at System.ComponentModel.TypeDescriptor.GetPropertiesImpl(Object component, Attribute[] attributes, Boolean noCustomTypeDesc, Boolean noAttributes)
       at System.Windows.PropertyPath.ResolvePropertyName(String name, Object item, Type ownerType, Object context, Boolean throwOnError)
       at System.Windows.PropertyPath.ResolvePropertyName(Int32 level, Object item, Type ownerType, Object context)
       at MS.Internal.Data.PropertyPathWorker.GetInfo(Int32 k, Object item, SourceValueState& svs)
       at MS.Internal.Data.PropertyPathWorker.ReplaceItem(Int32 k, Object newO, Object parent)
       at MS.Internal.Data.PropertyPathWorker.UpdateSourceValueState(Int32 k, ICollectionView collectionView, Object newValue, Boolean isASubPropertyChange)
       at MS.Internal.Data.ClrBindingWorker.AttachDataItem()
       at System.Windows.Data.BindingExpression.Activate(Object item)
       at System.Windows.Data.BindingExpression.AttachToContext(AttachAttempt attempt)
       at System.Windows.Data.BindingExpression.AttachOverride(DependencyObject target, DependencyProperty dp)
       at System.Windows.Data.BindingExpressionBase.Attach(DependencyObject target, DependencyProperty dp)
       at System.Windows.StyleHelper.GetInstanceValue(UncommonField`1 dataField, DependencyObject container, FrameworkElement feChild, FrameworkContentElement fceChild, Int32 childIndex, DependencyProperty dp, Int32 i, EffectiveValueEntry& entry)
       at System.Windows.StyleHelper.GetChildValueHelper(UncommonField`1 dataField, ItemStructList`1& valueLookupList, DependencyProperty dp, DependencyObject container, FrameworkObject child, Int32 childIndex, Boolean styleLookup, EffectiveValueEntry& entry, ValueLookupType& sourceType, FrameworkElementFactory templateRoot)
       at System.Windows.StyleHelper.GetChildValue(UncommonField`1 dataField, DependencyObject container, Int32 childIndex, FrameworkObject child, DependencyProperty dp, FrugalStructList`1& childRecordFromChildIndex, EffectiveValueEntry& entry, ValueLookupType& sourceType, FrameworkElementFactory templateRoot)
       at System.Windows.StyleHelper.GetValueFromTemplatedParent(DependencyObject container, Int32 childIndex, FrameworkObject child, DependencyProperty dp, FrugalStructList`1& childRecordFromChildIndex, FrameworkElementFactory templateRoot, EffectiveValueEntry& entry)
       at System.Windows.StyleHelper.ApplyTemplatedParentValue(DependencyObject container, FrameworkObject child, Int32 childIndex, FrugalStructList`1& childRecordFromChildIndex, DependencyProperty dp, FrameworkElementFactory templateRoot)
       at System.Windows.StyleHelper.InvalidatePropertiesOnTemplateNode(DependencyObject container, FrameworkObject child, Int32 childIndex, FrugalStructList`1& childRecordFromChildIndex, Boolean isDetach, FrameworkElementFactory templateRoot)
       at System.Windows.FrameworkTemplate.InvalidatePropertiesOnTemplate(DependencyObject container, Object currentObject)
       at System.Windows.FrameworkTemplate.<>c__DisplayClass6.<LoadOptimizedTemplateContent>b__3(Object sender, XamlObjectEventArgs args)
       at System.Xaml.XamlObjectWriter.Logic_CreateAndAssignToParentStart(ObjectWriterContext ctx)
       at System.Xaml.XamlObjectWriter.WriteStartMember(XamlMember property)
       at System.Windows.FrameworkTemplate.LoadTemplateXaml(XamlReader templateReader, XamlObjectWriter currentWriter)
  InnerException: 

update

below is the line where the exception is caught:

var value = property.GetValue(this, null);

which is part of this method

    public override int GetHashCode() {
        unchecked {
            IEnumerable<PropertyInfo> signatureProperties = GetSignatureProperties().ToArray();

            // It's possible for two objects to return the same hash code based on 
            // identically valued properties, even if they're of two different types, 
            // so we include the object's type in the hash calculation
            var hashCode = GetType().GetHashCode();

            foreach (var property in signatureProperties) {
                var value = property.GetValue(this, null);

                if (value != null)
                    hashCode = (hashCode * HASH_MULTIPLIER) ^ value.GetHashCode();
            }

            if (signatureProperties.Any())
                return hashCode;

            // If no properties were flagged as being part of the signature of the object,
            // then simply return the hashcode of the base object as the hashcode.
            return base.GetHashCode();
        }
    }

Answer 1

When you call property.GetValue(, the second parameter is for specifying the index value to an indexer property. If a property is an indexer and you pass null, then you are going to get an exception. You need to determine which properties are indexers and have a value to pass in as this second parameter.

To add a reference, according to the documentation (under Exceptions section), a TargetParameterCountException is thrown when:

The number of parameters in index does not match the number of
parameters the indexed property takes.

which sounds like your exact scenario.

Hope this helps!