How about change the type of ManipulationDeltaEventArgs.Manipulators property to ReadOnlyCollection

[lindexi]

Today, the Manipulators property in ManipulationDeltaEventArgs class is the IEnumerable<IManipulator> type.

wpf/src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Input/ManipulationDeltaEventArgs.cs

Lines 230 to 240 in e977c7e

	public IEnumerable<IManipulator> Manipulators
	{
	get
	{
	if (_manipulators == null)
	{
	_manipulators = ((ManipulationDevice)Device).GetManipulatorsReadOnly();
	}
	return _manipulators;
	}
	}

But the actual type of Manipulators is the ReadOnlyCollection<IManipulator>.

wpf/src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Input/ManipulationDevice.cs

Lines 219 to 229 in e977c7e

	internal IEnumerable<IManipulator> GetManipulatorsReadOnly()
	{
	if (_manipulators != null)
	{
	return new ReadOnlyCollection<IManipulator>(_manipulators);
	}
	else
	{
	return new ReadOnlyCollection<IManipulator>(new List<IManipulator>(2));
	}
	}

And the type of actual data is the List<IManipulator>.

wpf/src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Input/ManipulationDevice.cs

Line 521 in e977c7e

private List<IManipulator> _manipulators;