feat(controls): Add TitleBar CenterContent property (#1484)

* ADD TitleBar CenterContent property to allow content in the middle of TitleBar

* Update TitleBar.cs

minimizing changes

* bind center area VerticalAlignment to VerticalContentAlignment of TitleBar

* Restored missing statements

* untabify

* Fix formatting in TitleBar.cs

---------

Co-authored-by: pomian <13592821+pomianowski@users.noreply.github.com>

Author: luca-domenichini

src/Wpf.Ui/Controls/TitleBar/TitleBar.cs

@@ -66,6 +66,16 @@ public partial class TitleBar : System.Windows.Controls.Control, IThemeControl
         new PropertyMetadata(null)
     );
 
+    /// <summary>
+    /// Property for <see cref="CenterContent"/>.
+    /// </summary>
+    public static readonly DependencyProperty CenterContentProperty = DependencyProperty.Register(
+        nameof(CenterContent),
+        typeof(object),
+        typeof(TitleBar),
+        new PropertyMetadata(null)
+    );
+
     /// <summary>
     /// Property for <see cref="TrailingContent"/>.
     /// </summary>
@@ -233,6 +243,15 @@ public object? Header
         set => SetValue(HeaderProperty, value);
     }
 
+    /// <summary>
+    /// Gets or sets the content displayed in the center of the <see cref="TitleBar"/>.
+    /// </summary>
+    public object? CenterContent
+    {
+        get => GetValue(CenterContentProperty);
+        set => SetValue(CenterContentProperty, value);
+    }
+
     /// <summary>
     /// Gets or sets the content displayed in right side of the <see cref="TitleBar"/>.
     /// </summary>
@@ -685,20 +704,15 @@ or PInvoke.WM_NCLBUTTONUP
 
         if (message == PInvoke.WM_NCHITTEST)
         {
-            if (TrailingContent is UIElement || Header is UIElement)
+            if (TrailingContent is UIElement || Header is UIElement || CenterContent is UIElement)
             {
+                UIElement? headerLeftUIElement = Header as UIElement;
+                UIElement? headerCenterUIElement = CenterContent as UIElement;
                 UIElement? headerRightUiElement = TrailingContent as UIElement;
 
-                if (Header is UIElement headerLeftUIElement && headerLeftUIElement != _titleBlock)
-                {
-                    isMouseOverHeaderContent =
-                        headerLeftUIElement.IsMouseOverElement(lParam)
-                        || (headerRightUiElement?.IsMouseOverElement(lParam) ?? false);
-                }
-                else
-                {
-                    isMouseOverHeaderContent = headerRightUiElement?.IsMouseOverElement(lParam) ?? false;
-                }
+                isMouseOverHeaderContent = (headerLeftUIElement is not null && headerLeftUIElement != _titleBlock && headerLeftUIElement.IsMouseOverElement(lParam))
+                    || (headerCenterUIElement?.IsMouseOverElement(lParam) ?? false)
+                    || (headerRightUiElement?.IsMouseOverElement(lParam) ?? false);
             }
 
             htResult = GetWindowBorderHitTestResult(hwnd, lParam);

src/Wpf.Ui/Controls/TitleBar/TitleBar.xaml

@@ -137,6 +137,7 @@
                                 <ColumnDefinition Width="Auto" />
                                 <ColumnDefinition Width="*" />
                                 <ColumnDefinition Width="Auto" />
+                                <ColumnDefinition Width="Auto" />
                             </Grid.ColumnDefinitions>
 
                             <!--  Title text or other header content  -->
@@ -145,15 +146,22 @@
                                 HorizontalAlignment="Left"
                                 Content="{TemplateBinding Header}" />
 
-                            <!--  Additional header content  -->
+                            <!--  Centered content  -->
                             <ContentPresenter
                                 Grid.Column="1"
+                                HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}"
+                                VerticalAlignment="{TemplateBinding VerticalContentAlignment}"
+                                Content="{TemplateBinding CenterContent}" />
+
+                            <!--  Additional header content  -->
+                            <ContentPresenter
+                                Grid.Column="2"
                                 HorizontalAlignment="Right"
                                 Content="{TemplateBinding TrailingContent}" />
 
                             <!--  Navigation buttons - Close, Restore, Maximize, Minimize  -->
                             <Grid
-                                Grid.Column="2"
+                                Grid.Column="3"
                                 HorizontalAlignment="Right"
                                 VerticalAlignment="Top">
                                 <Grid.ColumnDefinitions>