Proposal: Add `TabDisplayMode` for `TabView`

[kingcean]

Summary

When we implement a browser with tabs, we may need to hide the tabs on full screen. So please add a property TabDisplayMode for TabView class to allow to do so. Its type is an Enum with following values.

• Default: The tabs bar and the content are shown top-bottom.
• Overlay: The tabs bar covers the content and does not take up space in the control layout.
• Hidden: The tabs bar is hidden. Only shows the content.

Rationale

• It allows developers to control if the tab is visible. It will be useful to hide when the content of the current tab selected should cover the screen more (just like in full-screen or other focus mode).
• It allows developers to have opportunities to slide in the tabs when the tab was set invisibility, such as when the pointer is on the edge or somewhere.

Important Notes

Following is the Enum definition for example mentioned above.

public enum TabDisplayMode : byte
{
    Default = 0,
    Overlay = 1,
    Hidden = 2,
}

And add the property to TabView.

[Windows.Foundation.Metadata.MarshalingBehavior(Windows.Foundation.Metadata.MarshalingType.Agile)]
[Windows.Foundation.Metadata.Threading(Windows.Foundation.Metadata.ThreadingModel.Both)]
[Windows.UI.Xaml.Markup.ContentProperty(Name="TabItems")]
[Windows.Foundation.Metadata.ContractVersion(typeof(Microsoft.UI.Xaml.XamlContract), 65536)]
public class TabView : Control
{
+    public TabDisplayMode TabDisplayMode { get; set; }
}

Following is the usage example.

<Grid>
    <Border x:Name="TopElement"
        Height="1"
        VerticalAlignment="Top"
        PointerEntered="TopElement_PointerEntered"
        PointerExited="TopElement_PointerExited"  />
    <TabView x:Name="TabViewElement" >
        <!-- Some tabs -->
    </TabView>
</Grid>

private void TopElement_PointerEntered(object sender, PointerRoutedEventArgs e)
    => TabViewElement.TabDisplayMode = TabDisplayMode.Overlay;

private void TopElement_PointerExited(object sender, PointerRoutedEventArgs e)
    => TabViewElement.TabDisplayMode = TabDisplayMode..Hidden;

Open Questions

It would be great if WinUI team could also add vertical tabs.

[kingcean]

Is there any plan to add such feature? Thanks!