WindowManagementApi 1.1.0

Window Management API

A general-purpose .NET 10 library for programmatic Windows window management with first-class multi-monitor, mixed-DPI support.

Prerequisites

• Windows 10 or 11
• .NET 10.0 or later
• Process must be configured for per-monitor v2 DPI awareness

Quick Start

Standalone usage

using WindowManagement;

await using var manager = WindowManagementFactory.Create();

// List all Alt+Tab windows
var windows = manager.GetAll();
foreach (var w in windows)
    Console.WriteLine($"{w.ProcessName}: {w.Title} ({w.Bounds})");

// Snap the foreground window to the left half of the primary monitor
var foreground = manager.GetForeground();
if (foreground != null)
    await manager.SnapAsync(foreground, manager.Monitors.Primary, SnapPosition.Left);

With dependency injection

using WindowManagement.DependencyInjection;

services.AddWindowManagement();

With Autofac

using WindowManagement.DependencyInjection;

builder.RegisterModule(new WindowManagementModule());

Then inject IWindowManager:

public class MyService(IWindowManager windowManager)
{
    public async Task SnapToLeft()
    {
        var foreground = windowManager.GetForeground();
        if (foreground != null)
            await windowManager.SnapAsync(foreground, windowManager.Monitors.Primary, SnapPosition.Left);
    }
}

Window Filtering

// Default: Alt+Tab window set
var windows = manager.GetAll();

// Filter by process
var windows = manager.GetAll(f => f.WithProcess("notepad"));

// Filter by title with wildcards
var windows = manager.GetAll(f => f.WithTitle("*.txt*"));

// Exclude minimized windows
var windows = manager.GetAll(f => f.ExcludeMinimized());

// Raw enumeration (no Alt+Tab filtering)
var windows = manager.GetAll(f => f.Unfiltered());

// Custom predicate
var windows = manager.GetAll(f => f.Where(w => w.Bounds.Width > 500));

Window Properties

IWindow provides rich snapshot data for each window:

var window = manager.GetForeground();
if (window != null)
{
    Console.WriteLine($"Title: {window.Title}");
    Console.WriteLine($"Process: {window.ProcessName} (PID {window.ProcessId})");
    Console.WriteLine($"Bounds: {window.Bounds}, Client: {window.ClientBounds}");
    Console.WriteLine($"State: {window.State}, Resizable: {window.IsResizable}");
    Console.WriteLine($"DPI: {window.Dpi}, Awareness: {window.DpiAwareness}");
    Console.WriteLine($"Topmost: {window.IsTopmost}, ClickThrough: {window.IsClickThrough}");
}

DPI Awareness

Check a window's DPI awareness level to handle cross-monitor positioning of legacy apps:

if (window.DpiAwareness == DpiAwareness.Unaware)
    Console.WriteLine("Legacy app — Windows virtualizes DPI for this window");

Values: Unaware, SystemAware, PerMonitorAware, PerMonitorAwareV2

Extended Window Styles

Toggle click-through and tool-window styles:

// Make an overlay window click-through (WS_EX_TRANSPARENT)
await manager.SetClickThroughAsync(window, true);

// Hide window from Alt+Tab (WS_EX_TOOLWINDOW)
await manager.SetToolWindowAsync(window, true);

For advanced style manipulation, use the low-level API:

var style = windowApi.GetExtendedStyle(handle);
style |= ExtendedWindowStyle.NoActivate;
windowApi.SetExtendedStyle(handle, style);

Window Events (R3)

manager.Created.Subscribe(e => Console.WriteLine($"Created: {e.Title}"));
manager.Moved.Subscribe(e => Console.WriteLine($"Moved: {e.Title} -> {e.NewBounds}"));
manager.Monitors.Connected.Subscribe(e => Console.WriteLine($"Monitor connected: {e.DeviceName}"));

Move/Size Events

Detect when a user starts and finishes dragging or resizing a window:

manager.MoveSizeStarted.Subscribe(e =>
    Console.WriteLine($"Drag started: {e.Title}"));

manager.MoveSizeEnded.Subscribe(e =>
    Console.WriteLine($"Drag ended: {e.Title} from {e.OldBounds} to {e.NewBounds}"));

Error Handling

The library throws WindowManagementException when Win32 operations fail (e.g., SetWindowPos, GetWindowRect). WindowNotFoundException (a subclass) is thrown when a window handle becomes invalid.

try
{
    await manager.SnapAsync(window, monitor, SnapPosition.Left);
}
catch (WindowNotFoundException)
{
    // Window was closed
}
catch (WindowManagementException ex)
{
    // Win32 operation failed
    Console.WriteLine(ex.Message);
}

WindowRect enforces non-negative Width and Height:

var rect = new WindowRect(0, 0, 800, 600);    // OK
var bad  = new WindowRect(0, 0, -1, 600);     // throws ArgumentOutOfRangeException
var also = rect with { Width = -1 };           // throws ArgumentOutOfRangeException

Low-Level API

For advanced consumers who need direct Win32 access with correct DPI math:

// Inject or resolve
IWindowApi windowApi = ...;
IDisplayApi displayApi = ...;

var handles = windowApi.Enumerate(altTabOnly: true);
var bounds = windowApi.GetBounds(handle);
windowApi.SetBounds(handle, new WindowRect(0, 0, 800, 600));

// DPI awareness per window
var awareness = windowApi.GetDpiAwareness(handle); // Unaware, SystemAware, PerMonitorAware, PerMonitorAwareV2

// Extended window styles
var style = windowApi.GetExtendedStyle(handle);
windowApi.SetExtendedStyle(handle, style | ExtendedWindowStyle.Transparent);

var monitors = displayApi.GetAll();
var logical = displayApi.PhysicalToLogical(bounds, monitor.Handle);