Add advanced option to start the window hidden

Resolves #50

Also will hide the window while it's loading in case the host is slow between instructions.

DesktopClock/MainWindow.xaml

@@ -14,6 +14,7 @@
         WindowStyle="None"
         ResizeMode="NoResize"
         SizeToContent="WidthAndHeight"
+        Opacity="0"
         Topmost="{Binding Topmost, Source={x:Static p:Settings.Default}, Mode=TwoWay}"
         FontFamily="{Binding FontFamily, Source={x:Static p:Settings.Default}, Mode=OneWay}"
         MouseDown="Window_MouseDown"

DesktopClock/MainWindow.xaml.cs

@@ -53,7 +53,7 @@ public MainWindow()
 
         Settings.Default.PropertyChanged += (s, e) => Dispatcher.Invoke(() => Settings_PropertyChanged(s, e));
 
-        // Not done through binding due to what's explained in the comment in HideForNow().
+        // Not done through binding due to what's explained in the comment in WindowUtil.HideFromScreen().
         ShowInTaskbar = Settings.Default.ShowInTaskbar;
 
         CurrentTimeOrCountdownString = Settings.Default.LastDisplay;
@@ -88,11 +88,7 @@ public void HideForNow()
             Settings.Default.TipsShown |= TeachingTips.HideForNow;
         }
 
-        // Minimize the window and update the ShowInTaskbar property to keep it hidden if needed.
-        // https://stackoverflow.com/a/28239057.
-        ShowInTaskbar = true;
-        WindowState = WindowState.Minimized;
-        ShowInTaskbar = Settings.Default.ShowInTaskbar;
+        this.HideFromScreen();
     }
 
     /// <summary>
@@ -446,6 +442,16 @@ private void Window_SourceInitialized(object sender, EventArgs e)
 
         // Now that everything's been initially rendered and laid out, we can start listening for changes to the size to keep the window right-aligned.
         SizeChanged += Window_SizeChanged;
+
+        if (Settings.Default.StartHidden)
+        {
+            _trayIcon?.ShowNotification("Started hidden", "Icon is in the tray");
+            this.HideFromScreen();
+        }
+
+        // Show the window now that it's finished loading.
+        // This was mainly done to stop the StartHidden option from flashing the window briefly.
+        Opacity = 1;
     }
 
     private void Window_ContentRendered(object sender, EventArgs e)

DesktopClock/Properties/Settings.cs

@@ -151,10 +151,18 @@ private Settings()
     public int Height { get; set; } = 48;
 
     /// <summary>
-    /// Runs the app on startup.
+    /// Runs the app when the user logs in.
     /// </summary>
+    /// <remarks>
+    /// A registry key is created or deleted.
+    /// </remarks>
     public bool RunOnStartup { get; set; } = false;
 
+    /// <summary>
+    /// Starts the app in the "Hide for now" state.
+    /// </summary>
+    public bool StartHidden { get; set; } = false;
+
     /// <summary>
     /// Allows moving the clock by dragging.
     /// </summary>

DesktopClock/WindowUtil.cs

@@ -0,0 +1,19 @@
+using System.Windows;
+
+namespace DesktopClock;
+
+public static class WindowUtil
+{
+    /// <summary>
+    /// Hides the window until the user opens it through the taskbar, tray, alt-tab, etc.
+    /// </summary>
+    public static void HideFromScreen(this Window window)
+    {
+        // Minimize the window and update the ShowInTaskbar property to keep it hidden if needed.
+        // https://stackoverflow.com/a/28239057.
+        var wasShownInTaskbar = window.ShowInTaskbar;
+        window.ShowInTaskbar = true;
+        window.WindowState = WindowState.Minimized;
+        window.ShowInTaskbar = wasShownInTaskbar;
+    }
+}