--- title: IWindowService order: 700 seealso: [] --- # IWindowService `IWindowService` provides a platform-agnostic way to show non-modal windows from your ViewModels. The ViewModels remain completely decoupled from Avalonia window types. Main features include: - Displaying non-modal windows. - ViewModel-driven windows — A window shown is defined by a custom ViewModel. You can specify the content of the target window using the ViewModel's `Content` property, or using the `ViewLocatorAttribute` applied to the window's ViewModel. - Automatic owner — The active application window becomes the target window's owner. The active window is automatically resolved through the `IWindowsManager` service. ## Interface Definition ```csharp public interface IWindowService { // Show a non-modal window driven by a ViewModel. void Show(T viewModel, string? caption = null) where T : IWindowAwareViewModel; } ``` | Parameter | Type | Description | |-----------|------|-------------| | `viewModel` | `T` | The ViewModel of the target window to display. The `viewModel` object must implement the `IWindowAwareViewModel` interface. You can derive your window's ViewModel from the `WindowAwareViewModel` class, which already implements this interface and adds the view-location infrastructure. | | `caption` | `string?` | The window caption. When set to `null`, the caption is taken from the ViewModel's `Title` property (`IWindowAwareViewModel.Title`). | The `Show` method returns immediately after showing the window and does not wait for it to close. **Exceptions:** - `ArgumentNullException` — If the `viewModel` parameter is `null`. ## How to Use IWindowService 1. Create a ViewModel for the target non-modal window. For example, you can derive it from the `WindowAwareViewModel` class. 2. Specify the target window's content using one of the following approaches: - Define a View (`UserControl`) that represents the target window's content. Set the `ViewLocatorAttribute` for the ViewModel to link this ViewModel to the created View. - Set the `Content` property of the window's ViewModel (`WindowAwareViewModel.Content`) explicitly. 3. In the ViewModel in which you need to display the target window, call the `IWindowService.Show` method. Pass the target window's ViewModel to the `Show` method. The `Show` method returns immediately, and the window shown stays open until a user closes it. ### Access the Service There are two ways to access an `IWindowService` object in your ViewModel: - Through the `Service()` helper method. This is a convenient approach to obtain registered application services shipped with the Eremex Controls library. - Through constructor injection. #### Service() Helper Implement a helper `Service()` method in your ViewModel to get a requested service using the static `ApplicationServicesContext.GetRequiredService()` method. ```csharp using Eremex.AvaloniaUI.Controls.ApplicationServices; using CommunityToolkit.Mvvm.Input; public partial class MyViewModel : ObservableObject { // Provides access to any registered service protected static T Service() where T : class => ApplicationServicesContext.GetRequiredService(); [RelayCommand] private void ShowWindow() { // Resolve the service and show the window Service().Show( new MyWindowViewModel("Non-modal window")); } } ``` In the App.axaml.cs file, ensure that Eremex application services are registered using `SimpleServiceProvider` and `ApplicationServicesContext` as follows: ```csharp public class App : Application { public override void OnFrameworkInitializationCompleted() { RegisterApplicationServices(); //... } static void RegisterApplicationServices() { // Register built-in services. var serviceProvider = new SimpleServiceProvider(); ApplicationServicesContext.RegisterApplicationServices(serviceProvider.AddSingleton); ApplicationServicesContext.SetCurrent(serviceProvider); } } ``` #### Constructor Injection Implement a constructor in your ViewModel with `IWindowService` as a parameter. When you instantiate the ViewModel, pass the service object to this constructor. ```csharp public partial class MyViewModel { private readonly IWindowService _windowService; public MyViewModel(IWindowService windowService) { _windowService = windowService; } [RelayCommand] private void ShowWindow() { _windowService.Show(new MyWindowViewModel("Non-modal window")); } } ``` ### Create a Window's ViewModel You need to create a ViewModel for the non-modal window to show. The ViewModel must implement the `IWindowAwareViewModel` interface. The simplest approach is to derive the ViewModel from the `WindowAwareViewModel` class, which already implements the `IWindowAwareViewModel` interface and handles view location. #### Define the Window's Content Using ViewLocatorAttribute 1. Create a View (`UserControl`) with the controls you need to display in the target window. 2. Decorate the window's ViewModel with `ViewLocatorAttribute`, passing the type of the View. When the `IWindowService.Show` method is called, the ViewModel creates an Avalonia window, instantiates the specified View (`UserControl`), and places it as the window's content. The ViewModel never needs to reference the View type directly. #### Example The following example uses the `IWindowService` service to show a non-modal window whose content is specified by a custom View. See the complete code in the [Controls Demo](/docs/index.md#demo-application) application. ![app-services-iwindowservice-example](/docs/images/app-services-iwindowservice-example.png) **Non-modal window's ViewModel** ```csharp using Eremex.AvaloniaUI.Controls.ApplicationServices; [ViewLocator(typeof(WindowServiceWindowView))] public class WindowServiceWindowViewModel : WindowAwareViewModel { private string statusText; public string StatusText { get => statusText; private set { if (statusText == value) return; statusText = value; OnPropertyChanged(nameof(StatusText)); } } } ``` **Non-modal window's content (View)** ```xml ``` **Show the window** ```csharp [RelayCommand] private void ShowWindow() { string windowTitle = "Non-modal window"; Service().Show(new WindowServiceWindowViewModel(windowTitle)); } ``` #### Define the Window's Content Directly Use the ViewModel's `Content` property (`WindowAwareViewModel.Content`) to supply the window's content explicitly. ```csharp using Eremex.AvaloniaUI.Controls.ApplicationServices; public class MyWindowViewModel : WindowAwareViewModel { public MyWindowViewModel(string title) : base(title) { Content = "Window content"; } } ``` To show this window, use the following code: ```csharp Service().Show(new MyWindowViewModel("Non-modal window")); ``` ### Window's Title You can specify the window title using one of the following approaches: 1. Set the `caption` parameter of the `IWindowService.Show` method. 2. Set the `Title` property of the window's ViewModel. This property is in effect if the `caption` parameter of the `IWindowService.Show` method is `null`. ### Owner Window The owner is determined automatically through the `IWindowsManager` service. The active application window returned by this service becomes the target window's owner.