NavigationView: Fix SelectedItem not being unset when no NavigationViewItem is selected

[Felix-Dev]

Description

Fix issue where NavView's SelectedItem property was not set to null when all navigation view items are no longer selected.

Motivation and Context

Fixes #957

How Has This Been Tested?

Added API test.

[Felix-Dev]

@ranjeshj VS seems to suggest you worked on this test so I'll ask you: Is the ValidateSelection call here really necessary? (That method is the previous ValidateSelectionChangedEvent() just renamed.) It seems to me we are validating whether item 4 has been selected two times. Do we need both checks?

[marcelwgn]

@ranjeshj VS seems to suggest you worked on this test so I'll ask you: Is the ValidateSelection call here really necessary? (That method is the previous ValidateSelectionChangedEvent() just renamed.) It seems to me we are validating whether item 4 has been selected two times. Do we need both checks?

I think the idea is that we verify that the selection is also correct when selectionchanged got raised.

[Felix-Dev]

@chingucoding I just don't think we need to check whether the selection is correct twice. If we keep the check in the SelectionChanged event handler I don't think we need the other check (as we fail if event was not raised).

[marcelwgn]

@chingucoding I just don't think we need to check whether the selection is correct twice. If we keep the check in the SelectionChanged event handler I don't think we need the other check (as we fail if event was not raised).

We check if the selection is correct after we changed it and we also check if the selection is correct inside the SelectionChanged event. Techincally there could be a missmatch for example when we raise SelectionChanged to early.

[ranjeshj]

hat method is

That does look redundant. One thing this might be checking is that the timing is correct - that the selection state has been updated before raising the event and checking the state in the event handler gives us the expected values. If that is not covered by any of the other tests, then a comment might be useful. If that is being covered elsewhere, we can remove the check. Thanks.

[ranjeshj]

/azp run

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Azure Pipelines successfully started running 1 pipeline(s).

[Felix-Dev]

I kept the SelectionChanged event handler ValidateSelection checks and removed the specific Select checks as they are covered in their own tests (ValidateOneLevelSingleSelection() and ValidateOneLevelMultipleSelection()).

[ranjeshj]

/azp run

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Azure Pipelines successfully started running 1 pipeline(s).