Page View Model

Overview

PageViewModel<TContext> is the primary abstract class for top‑level pages in Asv.Avalonia. It inherits from ExtendableViewModel and implements the IPage interface.

Core Components

ExportPage attribute

You must apply the ExportPage(pageId) attribute to your page classes. This helps the MEF container find and register the view models.

[ExportPage(PageId)]
public class HomePageViewModel : PageViewModel<HomePageViewModel>
{
    public const string PageId = "home";
    
    // ...
}

Visuals

Each page contains a Title, Icon (with color), and Status (also with color). These can be customized as needed. This information is typically displayed in the shell tabs.

Close Workflow

When a page is closed via a tab, the TryCloseAsync method is called with the force argument set to false. It works as follows:

Asks child view‑models for pending‑close reasons via RequestChildCloseApproval. This method raises the PageCloseAttemptEvent routing event, which view models can catch to add restrictions.
If reasons to prevent closing exist, it shows the UnsavedChangesDialogPrefab. If the user cancels the dialog, the method returns early.
Calls RequestClose to notify the navigation service that the page is ready to be closed.

Command History

Each page contains its ICommandHistory property. It is used to store all commands executed on the page for undo and redo actions. See the Command Service article for more details.

Example

A simple usage example looks like this:

[ExportPage(PageId)]
public class HelloWorldPageViewModel : PageViewModel<HelloWorldPageViewModel>
{
    // A unique ID for the page, used for routing
    public const string PageId = "hello_world_page";
    
    // You can request dependencies from the MEF container via the constructor
    [ImportingConstructor]
    public HelloWorldPageViewModel(
        ICommandService cmd, 
        ILoggerFactory loggerFactory, 
        IDialogService dialogService) : base(PageId, cmd, loggerFactory, dialogService)
    {
        Title = "Hello Page";
        
        // Use the helper method to dispose the property automatically when the VM is disposed
        SavedText = new BindableReactiveProperty<string?>().DisposeItWith(Disposable);
    }
    
    // A property to bind in the view
    public BindableReactiveProperty<string?> SavedText { get; }
    
    public override IEnumerable<IRoutable> GetChildren()
    {
        // This page has no child view models (subpages or widgets), 
        // so we return an empty collection.
        return [];
    }

    protected override void AfterLoadExtensions()
    {
    }

    // Metadata about the module where this page is defined
    public override IExportInfo Source => SystemModule.Instance;
}

API

IPage

Represents a page in the application shell. Defines a common contract for navigable pages, including visual representation, command history, and controlled closing behavior.

Property	Type	Description
`Icon`	`MaterialIconKind`	Gets or sets the main icon representing the page in the tab menu.
`IconColor`	`AsvColorKind`	Gets or sets the color of the page icon.
`Status`	`MaterialIconKind?`	Gets or sets an optional status icon displayed alongside the page icon.
`StatusColor`	`AsvColorKind`	Gets or sets the color of the status icon.
`Title`	`string`	Gets or sets the title of the page displayed in the tab menu.
`History`	`ICommandHistory`	Gets the command history associated with the page.
`TryClose`	`ICommand`	Command that initiates an attempt to close the page.

Method	Return Type	Description
`TryCloseAsync(bool force)`	`ValueTask`	Attempts to close the page. When `force` is `false`, the page may request confirmation or block closing.

PageViewModel<TContext> : IPage

Represents a base view model for application pages.
Extends ExtendableViewModel<TContext> and provides standard page behavior such as close handling, change tracking, and integration with the shell navigation system.

Property	Type	Description
`HasChanges`	`BindableReactiveProperty<bool>`	Indicates whether the page has unsaved changes. Used to control close confirmation logic.
`Source`	`IExportInfo`	Gets export metadata describing the origin module of the page.

Method	Return Type	Description
`Dispose(bool disposing)`	`void`	Releases managed resources used by the page.

Last modified: 18 January 2026