Move horizontal TabView outside of PaneHolderPage

[lukeblevins]

Resolved / Related Issues

Itemize resolved / related issues by this PR.

• e.g. closes Enhancement: Enable dragging Files from top of sidebar #4144

Details of Changes

Prevent duplicate TabView instances on each page by moving the TabView to MainPage. This also includes an expanded drag region allowing users to drag the app window from the sidebar while keeping the right inset drag region which is now set a more reliable way. Finally, this PR adds back the removed TabViewItem transitions.

Validation

How did you test these changes?

• Built and ran the app
• Tested the changes for accessibility
• Tested for regressions in right inset region.

Screenshots (optional)

Design remains the same and still allows for sidebar resizing

[lukeblevins]

I can confirm a slight reduction in memory usage after this PR. For example, 10 open tabs went from 170 MB to 150 MB. The important part is that this PR fixes weird, user-facing behavior associated with having different instances of the TabView at once.

[d2dyno1]

For #4180

[yaira2]

The tab strip is shifted when the multitasking setting is set to horizontal and the window is sized small.

[lukeblevins]

@yaichenbaum This should be fixed now. I suggest merging this one despite the occasional weird behavior with the sidebar because it potentially fixes a crash during resize.

[yaira2]

@duke7553 What's the occasional weird behavior with the sidebar that you're talking about?

[lukeblevins]

@yaichenbaum The sidebar may enter a state where there is a gap between it and the content when it is in compact mode. This behavior is relatively rare and only occurs because the property change can't be communicated to the control on every open tab when their sidebar instances are unloaded due to the tab being unselected. This only occurs when multiple tabs are open and is usually easy to get back to normal by resizing the app window/toggling the sidebar open and closed.

[yaira2]

@duke7553 I'll check that out when I review this PR. We can probably resolve that and reduce memory usage by moving the sidebar out of PaneHolderPage as well.

[yaira2]

Great work! LGTM

[gave92]

Uff this crashes the app when toggling the "Enable dual pane mode" option in settings (because Window.Current.Content is not a MainPage when in Settings). Is there a better way to get a reference to the sidebar view model? If not we need to add some null checks.

[yaira2]

Uff this crashes the app when toggling the "Enable dual pane mode" option in settings (because Window.Current.Content is not a MainPage when in Settings). Is there a better way to get a reference to the sidebar view model? If not we need to add some null checks.

@gave92 Is that related to this issue https://appcenter.ms/orgs/FilesApp/apps/Files/crashes/errors/2706044090u/overview?

[gave92]

@yaichenbaum yeah but @duke7553 has a fix in his other PR.