Performance: pages under Personalization don't update Header

[Jay-o-Way]

The four pages under Personalization (Background, Accent color, Mouse pointers, Theme) don't update the NavigationView Header.

Reproduce:

• select Personalization
• open one of these pages (Header is "Personalization")
• go to another page (e.g. Settings)
• use "Back" button (on keyboard or mouse) to navigate back
• Header stays the same as for previous page

[ChenYiLins]

From our design point of view, this is actually not a bug, because the Header of NavigationView depends on the NavigationViewItem selected. However, for these four pages, this happens because they have no Item set.

    private void OnNavigated(object sender, NavigationEventArgs e)
    {
        if (_navigationView == null)
            return;

        if (e.SourcePageType == typeof(SettingsPage))
        {
            _navigationView.SelectedItem = _navigationView.SettingsItem;
            _navigationView.Header = ((ContentControl)_navigationView.SettingsItem).Content;
            return;
        }

        var selectedItem = GetSelectedItem(e.SourcePageType);
        if (selectedItem != null)
        {
            _navigationView.SelectedItem = selectedItem;
            _navigationView.Header = selectedItem.Content;
        }
    }

Adding subtree can solve this problem, but we have rejected this plan before.
Of course, there is also a solution, which is to add an public Header attribute for NavigationService. We can change it anywhere.

[Jay-o-Way]

I understand the cause. When you go to settings page and then back to one of these, the header stays with "Settings", so that is surely not right.
Let's add a header text where we can. Should be super easy.

[ChenYiLins]

I understand the cause. When you go to settings page and then back to one of these, the header stays with "Settings", so that is surely not right. Let's add a header text where we can. Should be super easy.

This issue has been solved in the latest PR #985.