From ba5e70510f5acfabc752bdd1cebd94bf1f01d0bd Mon Sep 17 00:00:00 2001
From: Kenny Guo <kennyguo@microsoft.com>
Date: Tue, 27 Jul 2021 16:36:23 +0800
Subject: [PATCH] Add hot key support for the back button in title bar

---
 src/Calculator/Views/MainPage.xaml.cs |  2 +-
 src/Calculator/Views/TitleBar.xaml    |  8 ++++-
 src/Calculator/Views/TitleBar.xaml.cs | 49 +++++++++++++++++++++++----
 3 files changed, 51 insertions(+), 8 deletions(-)

diff --git a/src/Calculator/Views/MainPage.xaml.cs b/src/Calculator/Views/MainPage.xaml.cs
index 1862b197..f6cc0aee 100644
--- a/src/Calculator/Views/MainPage.xaml.cs
+++ b/src/Calculator/Views/MainPage.xaml.cs
@@ -578,7 +578,7 @@ namespace CalculatorApp
             NarratorNotifier.Announce(announcement);
         }
 
-        private void TitleBarBackButtonClick(object sender, RoutedEventArgs e)
+        private void TitleBarBackButtonClick(object sender)
         {
             CloseSettingsPopup();
         }
diff --git a/src/Calculator/Views/TitleBar.xaml b/src/Calculator/Views/TitleBar.xaml
index 690609aa..5e243c15 100644
--- a/src/Calculator/Views/TitleBar.xaml
+++ b/src/Calculator/Views/TitleBar.xaml
@@ -28,6 +28,7 @@
                 <VisualState x:Name="BackButtonVisible">
                     <VisualState.Setters>
                         <Setter Target="BackButton.Visibility" Value="Visible"/>
+                        <Setter Target="BackButton.IsEnabled" Value="True"/>
                         <Setter Target="AppIcon.Margin" Value="0"/>
                     </VisualState.Setters>
                 </VisualState>
@@ -55,7 +56,12 @@
                     FontSize="12"
                     Click="BackButton_Click"
                     Content="&#xE72B;"
-                    Visibility="Collapsed"/>
+                    Visibility="Collapsed"
+                    IsEnabled="False">
+                <Button.KeyboardAccelerators>
+                    <KeyboardAccelerator Key="Left" Modifiers="Menu"/>
+                </Button.KeyboardAccelerators>
+            </Button>
 
             <Grid x:Name="BackgroundElement"
                   Grid.Column="1"
diff --git a/src/Calculator/Views/TitleBar.xaml.cs b/src/Calculator/Views/TitleBar.xaml.cs
index 23307113..1320b7d5 100644
--- a/src/Calculator/Views/TitleBar.xaml.cs
+++ b/src/Calculator/Views/TitleBar.xaml.cs
@@ -51,7 +51,9 @@ namespace CalculatorApp
             }));
 
         public event Windows.UI.Xaml.RoutedEventHandler AlwaysOnTopClick;
-        public event Windows.UI.Xaml.RoutedEventHandler BackButtonClick;
+
+        public delegate void BackButtonClickEventHandler(object sender);
+        public event BackButtonClickEventHandler BackButtonClick;
 
         private void OnLoaded(object sender, RoutedEventArgs e)
         {
@@ -63,6 +65,11 @@ namespace CalculatorApp
             m_accessibilitySettings.HighContrastChanged += OnHighContrastChanged;
             Window.Current.Activated += OnWindowActivated;
 
+            // Register the system back requested event
+            SystemNavigationManager.GetForCurrentView().BackRequested += System_BackRequested;
+            // Register the mouse back button event
+            Window.Current.CoreWindow.PointerPressed += CoreWindow_PointerPressed;
+
             // Register RequestedTheme changed callback to update title bar system button colors.
             m_rootFrameRequestedThemeCallbackToken =
                 Utils.ThemeHelper.RegisterAppThemeChangedCallback(RootFrame_RequestedThemeChanged);
@@ -87,10 +94,34 @@ namespace CalculatorApp
             m_uiSettings.ColorValuesChanged -= ColorValuesChanged;
             m_accessibilitySettings.HighContrastChanged -= OnHighContrastChanged;
             Window.Current.Activated -= OnWindowActivated;
+
+            SystemNavigationManager.GetForCurrentView().BackRequested -= System_BackRequested;
+            Window.Current.CoreWindow.PointerPressed -= CoreWindow_PointerPressed;
+
             Utils.ThemeHelper.
                 UnregisterAppThemeChangedCallback(m_rootFrameRequestedThemeCallbackToken);
         }
 
+        private void CoreWindow_PointerPressed(CoreWindow sender, PointerEventArgs e)
+        {
+            if (e.CurrentPoint.Properties.IsXButton1Pressed && BackButton.IsEnabled)
+            {
+                InvokeBackButton(sender);
+
+                e.Handled = true;
+            }
+        }
+
+        private void System_BackRequested(object sender, BackRequestedEventArgs e)
+        {
+            if (!e.Handled && BackButton.IsEnabled)
+            {
+                InvokeBackButton(sender) ;
+
+                e.Handled = true;
+            }
+        }
+
         private void RootFrame_RequestedThemeChanged(DependencyObject sender, DependencyProperty dp)
         {
             if(Frame.RequestedThemeProperty == dp)
@@ -211,6 +242,17 @@ namespace CalculatorApp
             AlwaysOnTopClick?.Invoke(this, e);
         }
 
+        // Called when BackButton invoked, for example, by clicking, access key and etc.
+        private void InvokeBackButton(object sender)
+        {
+            BackButtonClick?.Invoke(this);
+        }
+
+        private void BackButton_Click(object sender, RoutedEventArgs e)
+        {
+            InvokeBackButton(sender);
+        }
+
         // Dependency properties for the color of the system title bar buttons
         public Windows.UI.Xaml.Media.SolidColorBrush ButtonBackground
         {
@@ -294,10 +336,5 @@ namespace CalculatorApp
         private Windows.UI.ViewManagement.UISettings m_uiSettings;
         private Windows.UI.ViewManagement.AccessibilitySettings m_accessibilitySettings;
         private Utils.ThemeHelper.ThemeChangedCallbackToken m_rootFrameRequestedThemeCallbackToken;
-
-        private void BackButton_Click(object sender, RoutedEventArgs e)
-        {
-            BackButtonClick?.Invoke(this, e);
-        }
     }
 }