Customized titlebar cannot be dragged when tabs are added to the app window

[williamfigtree]

Describe the bug

When tabs are added to a tab view within an application window that has set ExtendsContentIntoTitleBar = true the titlebar becomes undraggable. Adding a second tab makes it draggable again. Adding a third makes it undraggable, and so on.

Also possibly relevant: when debugging the VisualStudio Xaml toolbar docks to the very top of the app window when it is undraggable. (see video below)

Steps to reproduce the bug

1. Create an application with a custom title bar and a tab view within the main window below the titlebar.
2. Add tabs within the tab view and note how the application switches bewteen draggable and undraggable.

Expected behavior

Adding tabs within an app should not impact the titlebar.

Screenshots

tabs-break-titlebar.mp4

NuGet package version

Windows App SDK 1.6.3: 1.6.250108002

Packaging type

Packaged (MSIX)

Windows version

Windows 10 version 22H2 (19045, 2022 Update)

IDE

Visual Studio 2022

Additional context

Minimal reproduction:
title-bar-bug-minimal-reproduction.zip

MainWindow.xaml

<?xml version="1.0" encoding="utf-8"?>
<Window
    x:Class="mrp_title_bar_drag_bug.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="using:mrp_title_bar_drag_bug"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d"
    Title="mrp-title-bar-drag-bug">

    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="*"/>
        </Grid.RowDefinitions>

        <Grid x:Name="AppTitleBar"  
      Height="32">
            <Grid.ColumnDefinitions>
                <ColumnDefinition x:Name="LeftPaddingColumn" Width="0"/>
                <ColumnDefinition/>
                <ColumnDefinition x:Name="RightPaddingColumn" Width="0"/>
            </Grid.ColumnDefinitions>
            <Image x:Name="TitleBarIcon" Source="ms-appx:///Assets/StoreLogo.png"
           Grid.Column="1"
           HorizontalAlignment="Left"
           Width="16" Height="16"
           Margin="8,0,0,0"/>
            <TextBlock x:Name="TitleBarTextBlock" 
               Text="Tabs break title bar demo" 
               Style="{StaticResource CaptionTextBlockStyle}"
               Grid.Column="1"
               VerticalAlignment="Center"
               Margin="28,0,0,0"/>
        </Grid>

        <TabView
            x:Name="TabView"
            Grid.Row="1"
            VerticalAlignment="Stretch" 
            HorizontalAlignment="Stretch" 
            IsAddTabButtonVisible="True"/>
    </Grid>
</Window>

MainWindow.xaml.cs

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Runtime.InteropServices.WindowsRuntime;
using Microsoft.UI.Xaml;
using Microsoft.UI.Xaml.Controls;
using Microsoft.UI.Xaml.Controls.Primitives;
using Microsoft.UI.Xaml.Data;
using Microsoft.UI.Xaml.Input;
using Microsoft.UI.Xaml.Media;
using Microsoft.UI.Xaml.Navigation;
using Windows.Foundation;
using Windows.Foundation.Collections;
using Microsoft.UI;           // Needed for WindowId.
using Microsoft.UI.Windowing; // Needed for AppWindow.
using WinRT.Interop;
using Windows.ApplicationModel;          // Needed for XAML/HWND interop.

// To learn more about WinUI, the WinUI project structure,
// and more about our project templates, see: http://aka.ms/winui-project-info.

namespace mrp_title_bar_drag_bug
{
    /// <summary>
    /// An empty window that can be used on its own or navigated to within a Frame.
    /// </summary>
    public sealed partial class MainWindow : Window
    {

        public MainWindow()
        {
            this.InitializeComponent();

            // Hide system title bar.
            ExtendsContentIntoTitleBar = true;

            TabView.AddTabButtonClick += TabView_AddTabButtonClick;
        }

        private void TabView_AddTabButtonClick(TabView sender, object args)
        {
            sender.TabItems.Add(new TabViewItem());
        }
    }
}

[ghost1372]

Try set TitleBar
SetTitleBar(AppTitleBar);

[williamfigtree]

That's fixed it. Thanks @ghost1372.

For reference the code needed in MainWindow.xaml.cs is:

ExtendsContentIntoTitleBar = true;
SetTitleBar(AppTitleBar);

FYI WinAppSdk team, this wasn't needed in the 1.5 WinAppSDK versions and if it's intended to be required should probably be mentioned here https://learn.microsoft.com/en-us/windows/apps/develop/title-bar.