Center window on startup (#28)

Author: Gitii

NativeInterop.Win32.Xaml/DesktopWindow.cs

@@ -1,6 +1,9 @@
 using System;
+using System.Diagnostics;
 using System.Runtime.InteropServices;
 using Windows.UI;
+using Windows.Win32;
+using Microsoft.UI;
 using Microsoft.UI.Xaml;
 using WinRT;
 
@@ -31,6 +34,8 @@ public DesktopWindow()
         _nativeWindow.AddListener(this);
     }
 
+    public StartupLocation StartupLocation { get; set; } = StartupLocation.Default;
+
     public int Width
     {
         get => _nativeWindow.Width;
@@ -217,9 +222,64 @@ public void OnActivated(NativeWindow nativeWindow)
         }
 
         _loaded = true;
+
+        UpdateInitialLocation();
+
         Loaded?.Invoke(this, new WindowLoadedEventArgs(this));
     }
 
+    private void UpdateInitialLocation()
+    {
+        switch (StartupLocation)
+        {
+            case StartupLocation.CenterScreen:
+                CenterOnScreen();
+                return;
+            case StartupLocation.CenterParentProcess:
+                CenterByParentProcess();
+                return;
+            default:
+                return;
+        }
+    }
+
+    /// <summary>
+    /// Center the window based on the main window of the parent process (the process which started this application) when it's first shown.
+    /// </summary>
+    public void CenterByParentProcess()
+    {
+        var parentProcess = Win32.ParentProcessUtilities.GetParentProcess();
+        if (parentProcess == null)
+        {
+            CenterOnScreen();
+            return;
+        }
+
+        var size = new System.Drawing.Size(Width, Height);
+        var monitorSize = DisplayInformation.GetMonitorSizeFromWindow(
+            parentProcess.MainWindowHandle
+        );
+
+        _nativeWindow.Position = new Point(
+            monitorSize.Width / 2 - size.Width / 2,
+            monitorSize.Height / 2 - size.Height / 2
+        );
+    }
+
+    /// <summary>
+    /// Center the window on the screen when it's first shown.
+    /// </summary>
+    public void CenterOnScreen()
+    {
+        var size = new System.Drawing.Size(Width, Height);
+        var monitorSize = DisplayInformation.GetMonitorSizeFromWindow(_hwnd);
+
+        _nativeWindow.Position = new Point(
+            monitorSize.Width / 2 - size.Width / 2,
+            monitorSize.Height / 2 - size.Height / 2
+        );
+    }
+
     private void Window_Activated(object sender, WindowActivatedEventArgs args)
     {
         if (_backdropConfigurationSource != null)

NativeInterop.Win32/DisplayInformation.cs

@@ -1,6 +1,8 @@
 using System;
+using System.Runtime.InteropServices;
 using Windows.Win32;
 using Windows.Win32.Foundation;
+using Windows.Win32.Graphics.Gdi;
 
 namespace NativeInterop.Win32;
 
@@ -24,4 +26,24 @@ public static float GetScalingFactor(IntPtr hwnd)
         float scalingFactor = (float)dpi / 96;
         return scalingFactor;
     }
+
+    public static Size GetMonitorSizeFromWindow(IntPtr hWnd)
+    {
+        var id = PInvoke.MonitorFromWindow(
+            new HWND(hWnd),
+            MONITOR_FROM_FLAGS.MONITOR_DEFAULTTONEAREST
+        );
+
+        MONITORINFO info = default;
+        info.cbSize = (uint)Marshal.SizeOf<MONITORINFO>();
+        if (PInvoke.GetMonitorInfo(id, ref info))
+        {
+            return new Size(
+                info.rcWork.right - info.rcWork.left,
+                info.rcWork.bottom - info.rcWork.top
+            );
+        }
+
+        throw new Exception("Failed to get monitor info");
+    }
 }

NativeInterop.Win32/NativeInterop.Win32.csproj

@@ -22,5 +22,6 @@
             <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
         </PackageReference>
         <PackageReference Include="Microsoft.WindowsAppSDK" Version="1.2.230217.4" />
+        <PackageReference Include="System.Management" Version="6.0.0" />
     </ItemGroup>
 </Project>

NativeInterop.Win32/NativeMethods.txt

@@ -15,3 +15,6 @@ LoadImage
 SendMessage
 DestroyIcon
 MINMAXINFO
+MonitorFromWindow
+GetMonitorInfo
+CREATESTRUCTW

NativeInterop.Win32/ParentProcessUtilities.cs

@@ -0,0 +1,77 @@
+using System.ComponentModel;
+using System.Diagnostics;
+using System.Runtime.InteropServices;
+using System;
+using System.Linq;
+using System.Management;
+
+namespace NativeInterop.Win32;
+
+/// <summary>
+/// A utility class to determine a process parent.
+/// </summary>
+[StructLayout(LayoutKind.Sequential)]
+public struct ParentProcessUtilities
+{
+    // These members must match PROCESS_BASIC_INFORMATION
+    internal IntPtr Reserved1;
+    internal IntPtr PebBaseAddress;
+    internal IntPtr Reserved2_0;
+    internal IntPtr Reserved2_1;
+    internal IntPtr UniqueProcessId;
+    internal IntPtr InheritedFromUniqueProcessId;
+
+    [DllImport("ntdll.dll")]
+    private static extern int NtQueryInformationProcess(
+        IntPtr processHandle,
+        int processInformationClass,
+        ref ParentProcessUtilities processInformation,
+        int processInformationLength,
+        out int returnLength
+    );
+
+    /// <summary>
+    /// Gets the parent process of the current process.
+    /// </summary>
+    /// <returns>An instance of the Process class.</returns>
+    public static Process? GetParentProcess()
+    {
+        return GetParentProcess(Process.GetCurrentProcess().Handle);
+    }
+
+    /// <summary>
+    /// Gets the parent process of specified process.
+    /// </summary>
+    /// <param name="id">The process id.</param>
+    /// <returns>An instance of the Process class.</returns>
+    public static Process? GetParentProcess(int id)
+    {
+        Process process = Process.GetProcessById(id);
+        return GetParentProcess(process.Handle);
+    }
+
+    /// <summary>
+    /// Gets the parent process of a specified process.
+    /// </summary>
+    /// <param name="handle">The process handle.</param>
+    /// <returns>An instance of the Process class.</returns>
+    public static Process? GetParentProcess(IntPtr handle)
+    {
+        ParentProcessUtilities pbi = new ParentProcessUtilities();
+        int status = NtQueryInformationProcess(handle, 0, ref pbi, Marshal.SizeOf(pbi), out _);
+        if (status != 0)
+        {
+            throw new Win32Exception(status);
+        }
+
+        try
+        {
+            return Process.GetProcessById(pbi.InheritedFromUniqueProcessId.ToInt32());
+        }
+        catch (ArgumentException)
+        {
+            // not found
+            return null;
+        }
+    }
+}

NativeInterop.Win32/Pinvoke.cs

@@ -1,6 +1,8 @@
 using System;
+using System.Drawing;
 using System.Runtime.InteropServices;
 using Windows.Win32.Foundation;
+using Windows.Win32.Graphics.Gdi;
 using Windows.Win32.UI.WindowsAndMessaging;
 
 // ReSharper disable once CheckNamespace

NativeInterop.Win32/StartupLocation.cs

@@ -0,0 +1,19 @@
+namespace NativeInterop.Win32;
+
+public enum StartupLocation
+{
+    /// <summary>
+    /// Let the operation system handle the initial location of the window.
+    /// </summary>
+    Default,
+
+    /// <summary>
+    /// Center the window on the screen when it's first shown.
+    /// </summary>
+    CenterScreen,
+
+    /// <summary>
+    /// Center the window based on the main window of the parent process (the process which started this application) when it's first shown.
+    /// </summary>
+    CenterParentProcess
+}

PackageInstaller/MainWindow.xaml

@@ -16,6 +16,7 @@
     SystemBackdropEnabled="True"
     mc:Ignorable="d"
     Closing="MainWindow_OnClosing"
+    StartupLocation="CenterParentProcess"
 >
     <controls:Grid HorizontalAlignment="Stretch" VerticalAlignment="Stretch">
         <controls:Grid.RowDefinitions>