Why does ObservableCollection throws an exception when being modified?
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by Oliver Hanappi
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Published on 2009-10-12T09:00:13Z
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2010/05/25
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wpf
Hi!
My application uses a WPF DataGrid. One of the columns is a template column that containts a combobox bound to an ObservableCollection of the entity which feeds the row. When I add a value to the ObservableCollection, a NullReferenceException is thrown.
Has anybody an idea why this happens? Here is the stacktrace of the exception:
at MS.Internal.Data.PropertyPathWorker.DetermineWhetherDBNullIsValid() at MS.Internal.Data.PropertyPathWorker.get_IsDBNullValidForUpdate() at MS.Internal.Data.ClrBindingWorker.get_IsDBNullValidForUpdate() at System.Windows.Data.BindingExpression.ConvertProposedValue(Object value) at System.Windows.Data.BindingExpressionBase.UpdateValue() at System.Windows.Data.BindingExpression.Update(Boolean synchronous) at System.Windows.Data.BindingExpressionBase.Dirty() at System.Windows.Data.BindingExpression.SetValue(DependencyObject d, DependencyProperty dp, Object value) at System.Windows.DependencyObject.SetValueCommon(DependencyProperty dp, Object value, PropertyMetadata metadata, Boolean coerceWithDeferredReference, OperationType operationType, Boolean isInternal) at System.Windows.DependencyObject.SetValue(DependencyProperty dp, Object value) at System.Windows.Controls.Primitives.Selector.UpdatePublicSelectionProperties() at System.Windows.Controls.Primitives.Selector.SelectionChanger.End() at System.Windows.Controls.Primitives.Selector.OnItemsChanged(NotifyCollectionChangedEventArgs e) at System.Windows.Controls.ItemsControl.OnItemCollectionChanged(Object sender, NotifyCollectionChangedEventArgs e) at System.Collections.Specialized.NotifyCollectionChangedEventHandler.Invoke(Object sender, NotifyCollectionChangedEventArgs e) at System.Windows.Data.CollectionView.OnCollectionChanged(NotifyCollectionChangedEventArgs args) at System.Windows.Controls.ItemCollection.System.Windows.IWeakEventListener.ReceiveWeakEvent(Type managerType, Object sender, EventArgs e) at System.Windows.WeakEventManager.DeliverEventToList(Object sender, EventArgs args, ListenerList list) at System.Windows.WeakEventManager.DeliverEvent(Object sender, EventArgs args) at System.Collections.Specialized.CollectionChangedEventManager.OnCollectionChanged(Object sender, NotifyCollectionChangedEventArgs args) at System.Windows.Data.CollectionView.OnCollectionChanged(NotifyCollectionChangedEventArgs args) at System.Windows.Data.ListCollectionView.ProcessCollectionChangedWithAdjustedIndex(NotifyCollectionChangedEventArgs args, Int32 adjustedOldIndex, Int32 adjustedNewIndex) at System.Windows.Data.ListCollectionView.ProcessCollectionChanged(NotifyCollectionChangedEventArgs args) at System.Windows.Data.CollectionView.OnCollectionChanged(Object sender, NotifyCollectionChangedEventArgs args) at System.Collections.ObjectModel.ObservableCollection`1.OnCollectionChanged(NotifyCollectionChangedEventArgs e) at System.Collections.ObjectModel.ObservableCollection`1.InsertItem(Int32 index, T item) at System.Collections.ObjectModel.Collection`1.Add(T item) at ORF.PersonBook.IdentityModule.Model.SubsidiaryModel.AddRoom(RoomModel room) in C:\Project\Phoenix\Development\src\ORF.PersonBook.IdentityModule\Model\SubsidiaryModel.cs:line 127
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