View Model Base

Overview

ViewModelBase is the fundamental abstract class for all view models in the Asv.Avalonia framework. It implements the IViewModel interface and provides core features for property notification, resource management, and logging.

Key Features:

Property Change Notifications: implements INotifyPropertyChanged.
Thread-Safe Disposal: a robust disposal pattern ensuring resources are released exactly once.
Navigation Support: implements ISupportId<NavigationId> to support argument initialization and routing.

Core Components

NavigationId

The IViewModel interface derives from the ISupportId<NavigationId> interface, which contains the Id property (of type NavigationId). It serves as the unique identifier for the view model instance. It's essential for:

Identifying: Distinguishing ViewModels within the application.
Navigation: Providing the path and parameters for routing (especially in RoutableViewModel).

You can initialize it with custom arguments using the InitArgs method.

Property Notification

IViewModel inherits from INotifyPropertyChanged.

To update properties, use the SetField method. It updates the backing field and automatically raises the PropertyChanged event only when the value has actually changed, preventing unnecessary UI updates.

Disposal Pattern

ViewModelBase implements a thread-safe disposal mechanism. While the base class itself holds no heavy resources, it establishes the pattern for all derived classes:

The public Dispose() method handles thread safety and prevents multiple disposal calls.
Derived classes should override the Dispose(bool disposing) method to perform actual cleanup (e.g., unsubscribing from events or stopping timers).

API

IViewModel

Defines a base contract for all view models in the application. This interface provides a unique identifier, supports property change notifications, and ensures proper disposal of resources.

Property	Type	Description
`IsDisposed`	`bool`	Gets a value indicating whether the view model has been disposed.

Method	Return Type	Description
`InitArgs(string? args)`	`void`	Initializes a navigation ID with the arguments.

ViewModelBase: IViewModel

Represents the base implementation of a view model that provides property change notifications and a proper disposal mechanism. This class is designed to be inherited by other view models.

Property	Type	Description
`Id`	`NavigationId`	A unique ViewModel ID.
`Logger`	`ILogger`	A logger.

Event	Type	Description
`PropertyChanged`	`PropertyChangedEventHandler?`	Occurs when a property value changes. Implements `INotifyPropertyChanged` to support UI binding updates.

Method	Return Type	Description
`Dispose()`	`void`	Releases resources used by the view model. Ensures that the disposal operation is only performed once.
`InternalInitArgs(NameValueCollection)`	`void`	Initializes Navigation ID with args.
`Dispose(bool disposing)`	`void`	Releases managed resources when disposing. This method must be implemented by derived classes to handle resource cleanup.
`ThrowIfDisposed()`	`void`	Throws an `ObjectDisposedException` if the view model has already been disposed. This ensures that disposed objects are not accessed unexpectedly.
`SetField<T>(ref T field, T value, string? propertyName)`	`bool`	Sets the field to the specified value and raises the `PropertyChanged` event if the value has changed.

`ViewModelBase.Dispose(bool disposing)`

Parameter	Type	Description
`disposing`	`bool`	`true` if called from `Dispose` method to release managed resources; otherwise, `false` if called from the finalizer.

`ViewModelBase.SetField<T>`

Parameter	Type	Description
`field`	`ref T`	The backing field reference.
`value`	`T`	The new value to set.
`propertyName`	`string?`	The name of the property that changed. Automatically set by the caller if not provided.

Last modified: 18 January 2026