NullReferenceException is thrown in the System.Windows.StyleHelper.GetExpression method

• .NET Core Version: .NET 7.0 SDK (v7.0.100-rc.2)
• Windows version: Version 21h1 (OS Build 19043.2130)
• Does the bug reproduce also in WPF for .NET Framework 4.8?: No
• Is this bug related specifically to tooling in Visual Studio (e.g. XAML Designer, Code editing, etc…)?: No

Problem description: An attempt to call the BindingOperations.GetBindingExpression method in .NET 7.0 leads to Null Reference Exception.

Actual behavior:

NullRerferenceException is thrown right at the moment when the following code is executed:

public App() {
    var viewSource = new CollectionViewSource();
    var be = BindingOperations.GetBindingExpression(viewSource, CollectionViewSource.SourceProperty);
}

The callstack indicates that the error is thrown in the System.Windows.StyleHelper.GetExpression method:

Callstack:

PresentationFramework.dll!System.Windows.StyleHelper.GetExpression(System.Windows.DependencyObject d, System.Windows.DependencyProperty dp)
PresentationFramework.dll!System.Windows.Data.BindingOperations.GetBindingExpressionBase(System.Windows.DependencyObject target, System.Windows.DependencyProperty dp)
PresentationFramework.dll!System.Windows.Data.BindingOperations.GetBindingExpression(System.Windows.DependencyObject target, System.Windows.DependencyProperty dp)
WpfApp1.dll!WpfApp1.App.App() Line 18
WpfApp1.dll!WpfApp1.App.Main()

Expected behavior:

No errors should be thrown.

Minimal repro:

Download and run the project. The error should be thrown right at the startup.

The project and screencast in the attachment illustrate the problematic behavior.

dxSample.zip screencast.mp4

[miloush]

@batzen this commit https://github.com/dotnet/wpf/commit/5769bbfd15d34e2ec98f44406862d831a514a895 broke it as static constructors no longer run

(to elaborate, FrameworkElement.cctor -> Style.cctor -> StyleHelper.RegisterAlternateExpressionStorage no longer runs in StyleHelper.GetExpression -> Helper.DowncastToFEorFCE)

In this very case one could argue that RegisterAlternateExpressionStorage should be called in StyleHelper cctor rather than Style one, but I am little worried about other side effects that PR might have caused by skipping static cctors of types.

[danlyons-softek]

@miloush Apologies for missing that detail - yes and no 😄

It looks like in all the cases I ran into issues, the code in question is assigning a value to Source on the CollectionViewSource. There are no direct references to BindingOperations.GetBindingExpression I can see.

However, according to the stack traces I see, the Source assignment ultimately triggers a call to StyleHelper.GetExpression via BindingOperations.GetBindingExpressionBase anyway.

Example:

public TreeNode()
{
    Children = new ObservableCollection<TreeNode>();
    ChildrenSource = new CollectionViewSource { Source = Children };
    ChildrenSource.SortDescriptions.Add(new SortDescription(nameof(Name), ListSortDirection.Ascending));
    ChildrenSource.IsLiveSortingRequested = true;
}

System.NullReferenceException : Object reference not set to an instance of an object.
   at System.Windows.StyleHelper.GetExpression(DependencyObject d, DependencyProperty dp)
   at System.Windows.Data.BindingOperations.GetBindingExpressionBase(DependencyObject target, DependencyProperty dp)
   at System.Windows.Data.CollectionViewSource.<EnsureView>b__103_0(Object x)
   at MS.Internal.Data.ViewManager.EnsureCollectionRecord(Object collection, Func`2 GetSourceItem)
   at MS.Internal.Data.ViewManager.GetExistingView(Object collection, CollectionViewSource cvs, Type collectionViewType, Func`2 GetSourceItem)
   at MS.Internal.Data.ViewManager.GetViewRecord(Object collection, CollectionViewSource cvs, Type collectionViewType, Boolean createView, Func`2 GetSourceItem)
   at MS.Internal.Data.DataBindEngine.GetViewRecord(Object collection, CollectionViewSource key, Type collectionViewType, Boolean createView, Func`2 GetSourceItem)
   at System.Windows.Data.CollectionViewSource.EnsureView(Object source, Type collectionViewType)
   at System.Windows.DependencyObject.OnPropertyChanged(DependencyPropertyChangedEventArgs e)
   at System.Windows.DependencyObject.NotifyPropertyChange(DependencyPropertyChangedEventArgs args)
   at System.Windows.DependencyObject.UpdateEffectiveValue(EntryIndex entryIndex, DependencyProperty dp, PropertyMetadata metadata, EffectiveValueEntry oldEntry, EffectiveValueEntry& newEntry, Boolean coerceWithDeferredReference, Boolean coerceWithCurrentValue, OperationType operationType)
   at System.Windows.DependencyObject.SetValueCommon(DependencyProperty dp, Object value, PropertyMetadata metadata, Boolean coerceWithDeferredReference, Boolean coerceWithCurrentValue, OperationType operationType, Boolean isInternal)
   at System.Windows.DependencyObject.SetValue(DependencyProperty dp, Object value)
   at TreeNode..ctor()