Major changes in MainPage: now is layout dependant (with a base, to prepare for Settings)

Main sub pages also changed to better work with Main (but needs improvement)
Added a Settings Page stub

ModernKeePass/Pages/BasePages/LayoutAwarePageBase.cs

@@ -0,0 +1,184 @@
+using System;
+using Windows.UI.Xaml;
+using Windows.UI.Xaml.Controls;
+using Windows.UI.Xaml.Data;
+using ModernKeePass.Common;
+using ModernKeePass.Interfaces;
+
+namespace ModernKeePass.Pages.BasePages
+{
+    public class LayoutAwarePageBase: Page
+    {
+        /// <summary>
+        /// NavigationHelper is used on each page to aid in navigation and 
+        /// process lifetime management
+        /// </summary>
+        public NavigationHelper NavigationHelper { get; }
+
+        public virtual ListView ListView { get; set; }
+        public virtual CollectionViewSource ListViewSource { get; set; }
+        public virtual IHasSelectableObject Model { get; set; }
+
+        public LayoutAwarePageBase()
+        {
+            // Setup the navigation helper
+            NavigationHelper = new NavigationHelper(this);
+            NavigationHelper.LoadState += navigationHelper_LoadState;
+            NavigationHelper.SaveState += navigationHelper_SaveState;
+
+            // Setup the logical page navigation components that allow
+            // the page to only show one pane at a time.
+            NavigationHelper.GoBackCommand = new RelayCommand(() => GoBack(), () => CanGoBack());
+
+            // Start listening for Window size changes 
+            // to change from showing two panes to showing a single pane
+            Window.Current.SizeChanged += Window_SizeChanged;
+            InvalidateVisualState();
+        }
+
+        protected void ListView_SelectionChanged(object sender, SelectionChangedEventArgs e)
+        {
+            // Invalidate the view state when logical page navigation is in effect, as a change
+            // in selection may cause a corresponding change in the current logical page.  When
+            // an item is selected this has the effect of changing from displaying the item list
+            // to showing the selected item's details.  When the selection is cleared this has the
+            // opposite effect.
+            if (!UsingLogicalPageNavigation()) return;
+            NavigationHelper.GoBackCommand.RaiseCanExecuteChanged();
+            InvalidateVisualState();
+        }
+
+        /// <summary>
+        /// Populates the page with content passed during navigation.  Any saved state is also
+        /// provided when recreating a page from a prior session.
+        /// </summary>
+        /// <param name="sender">
+        /// The source of the event; typically <see cref="Common.NavigationHelper"/>
+        /// </param>
+        /// <param name="e">Event data that provides both the navigation parameter passed to
+        /// <see cref="Frame.Navigate(Type, Object)"/> when this page was initially requested and
+        /// a dictionary of state preserved by this page during an earlier
+        /// session.  The state will be null the first time a page is visited.</param>
+        protected void navigationHelper_LoadState(object sender, LoadStateEventArgs e)
+        {
+            // TODO: Assign a bindable group to Me.DefaultViewModel("Group")
+            // TODO: Assign a collection of bindable items to Me.DefaultViewModel("Items")
+
+            if (e.PageState == null)
+            {
+                // When this is a new page, select the first item automatically unless logical page
+                // navigation is being used (see the logical page navigation #region below.)
+                if (!UsingLogicalPageNavigation() && ListViewSource.View != null)
+                {
+                    ListViewSource.View.MoveCurrentToFirst();
+                }
+            }
+            else
+            {
+                // Restore the previously saved state associated with this page
+                if (e.PageState.ContainsKey("SelectedItem") && ListViewSource.View != null)
+                {
+                    ListViewSource.View.MoveCurrentTo(e.PageState["SelectedItem"]);
+                }
+            }
+        }
+
+        /// <summary>
+        /// Preserves state associated with this page in case the application is suspended or the
+        /// page is discarded from the navigation cache.  Values must conform to the serialization
+        /// requirements of <see cref="Common.SuspensionManager.SessionState"/>.
+        /// </summary>
+        /// <param name="sender">The source of the event; typically <see cref="Common.NavigationHelper"/></param>
+        /// <param name="e">Event data that provides an empty dictionary to be populated with
+        /// serializable state.</param>
+        protected void navigationHelper_SaveState(object sender, SaveStateEventArgs e)
+        {
+            if (ListViewSource.View != null)
+            {
+                e.PageState["SelectedItem"] = Model?.SelectedItem;
+            }
+        }
+
+        #region Logical page navigation
+
+        // The split page is designed so that when the Window does have enough space to show
+        // both the list and the details, only one pane will be shown at at time.
+        //
+        // This is all implemented with a single physical page that can represent two logical
+        // pages.  The code below achieves this goal without making the user aware of the
+        // distinction.
+
+        protected const int MinimumWidthForSupportingTwoPanes = 768;
+
+        /// <summary>
+        /// Invoked to determine whether the page should act as one logical page or two.
+        /// </summary>
+        /// <returns>True if the window should show act as one logical page, false
+        /// otherwise.</returns>
+        protected bool UsingLogicalPageNavigation()
+        {
+            return Window.Current.Bounds.Width < MinimumWidthForSupportingTwoPanes;
+        }
+
+        /// <summary>
+        /// Invoked with the Window changes size
+        /// </summary>
+        /// <param name="sender">The current Window</param>
+        /// <param name="e">Event data that describes the new size of the Window</param>
+        protected void Window_SizeChanged(object sender, Windows.UI.Core.WindowSizeChangedEventArgs e)
+        {
+            InvalidateVisualState();
+        }
+
+        protected bool CanGoBack()
+        {
+            if (UsingLogicalPageNavigation() && ListView.SelectedItem != null)
+            {
+                return true;
+            }
+            return NavigationHelper.CanGoBack();
+        }
+        protected void GoBack()
+        {
+            if (UsingLogicalPageNavigation() && ListView.SelectedItem != null)
+            {
+                // When logical page navigation is in effect and there's a selected item that
+                // item's details are currently displayed.  Clearing the selection will return to
+                // the item list.  From the user's point of view this is a logical backward
+                // navigation.
+                ListView.SelectedItem = null;
+            }
+            else
+            {
+                NavigationHelper.GoBack();
+            }
+        }
+
+        protected void InvalidateVisualState()
+        {
+            var visualState = DetermineVisualState();
+            VisualStateManager.GoToState(this, visualState, false);
+            NavigationHelper.GoBackCommand.RaiseCanExecuteChanged();
+        }
+
+        /// <summary>
+        /// Invoked to determine the name of the visual state that corresponds to an application
+        /// view state.
+        /// </summary>
+        /// <returns>The name of the desired visual state.  This is the same as the name of the
+        /// view state except when there is a selected item in portrait and snapped views where
+        /// this additional logical page is represented by adding a suffix of _Detail.</returns>
+        protected string DetermineVisualState()
+        {
+            if (!UsingLogicalPageNavigation())
+                return "PrimaryView";
+
+            // Update the back button's enabled state when the view state changes
+            var logicalPageBack = UsingLogicalPageNavigation() && ListView?.SelectedItem != null;
+
+            return logicalPageBack ? "SinglePane_Detail" : "SinglePane";
+        }
+
+        #endregion
+    }
+}