Page View Model

Overview

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

Core Components

Registration

Pages must be registered in the DI container via the builder. Use the Pages.Register method to register a page with its view:

// In your mixin or Program.cs:
shell.Pages.Register<HomePageViewModel, HomePageView>(HomePageViewModel.PageId);

Visuals

Each page contains a Header, 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, which raises the bubbling PageCloseRequestedEvent to notify the shell that the page is ready to be closed. The shell handles the event and performs the actual close.

Undo History

Each page exposes an UndoHistory property of type IUndoHistory<IViewModel>, backed by the IUndoHistoryStore supplied through IPageContext. It records the operations performed on the page for undo and redo actions.

Example

A simple usage example looks like this:

public class HelloWorldPageViewModel : PageViewModel<HelloWorldPageViewModel>
{
    // A page type ID used for routing; uniqueness is validated at runtime
    public const string PageId = "hello_world_page";

    // Dependencies are injected via the constructor from the IServiceCollection container
    public HelloWorldPageViewModel(
        IPageContext context,
        ILoggerFactory loggerFactory,
        IDialogService dialogService,
        IExtensionService ext) : base(PageId, context, loggerFactory, dialogService, ext)
    {
        Header = "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; }

    protected override void AfterLoadExtensions()
    {
    }
}

This page has no child view models (subpages or widgets), so it does not override GetChildren() — the base implementation already returns an empty collection.

API

IPage

Represents a page in the application shell. Defines a common contract for navigable pages, including visual representation (icon, status, header), undo history, layout management, 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 an optional status icon displayed alongside the page icon.
`StatusColor`	`AsvColorKind`	Gets the color of the status icon.
`Header`	`string?`	Gets or sets the header (title) of the page displayed in the tab menu.
`UndoHistory`	`IUndoHistory<IViewModel>`	Gets the undo history associated with the page.
`LayoutManager`	`ILayoutManager<IViewModel>`	Gets the layout manager associated with the page.
`TryClose`	`ICommand`	Command that initiates an attempt to close the page.

Status and StatusColor are get-only on the contract; PageViewModel<TContext> exposes them as settable.

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.

IPageContext

Bundles the per-page construction data: the navigation arguments plus the undo and layout stores. PageContext is the standard implementation; NullPageContext.Instance is used at design time and returns NavArgs.Empty together with the null undo and layout stores.

Property	Type	Description
`NavArgs`	`NavArgs`	Gets the navigation arguments, forwarded to the base `ViewModel<TContext>`.
`UndoStore`	`IUndoHistoryStore`	Gets the store backing the page's `UndoHistory`.
`LayoutStore`	`ILayoutStore`	Gets the store backing the page's `LayoutManager`.

PageViewModel<TContext> : IPage

Represents a base view model for application pages.
Extends ViewModel<TContext> and provides standard page behavior such as close handling with restriction approval, undo history, layout management, and integration with the shell via routed events. Constrained to where TContext : class, IPage.

Constructor	Description
`PageViewModel(string typeId, IPageContext context, ILoggerFactory loggerFactory, IDialogService dialogService, IExtensionService ext)`	Protected. The `context` supplies the navigation arguments and the undo/layout stores.

Last modified: 17 July 2026