Radical Documentation
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  • Home
  • Presentation
    • AbstractViewModel
    • Conventions
      • Bootstrap Conventions
      • Runtime Conventions
      • Conventions override
    • Commands and DelegateCommand
    • IViewResolver
      • Default view behaviors
      • view life cycle events
        • Callback expectations
        • notify messages
    • Message broker MVVM built-in messages
    • Application boot process
      • Application configuration
      • Application shutdown
      • Singleton applications
    • AbstractMementoViewModel
      • Simple ViewModel graphs
      • Collections and complex ViewModel graphs
    • Validation and Validation Services
    • Resources
      • Services as resources
      • ViewModels as resources
  • UI Composition
    • UI Composition
      • Region content lifecycle
      • TabControl region
      • Create a custom region
  • Concepts
    • Inversion of Control
      • Third party DI containers
    • Entities
      • Property System
    • Messaging and Message Broker
      • POCO messages
      • Standalone message handlers
    • Observers
      • PropertyObserver
      • MementoObserver
      • BrokerObserver
  • Memento
    • Change Tracking Service
      • MementoEntity and MementoEntityCollection
      • Handling change tracking:
        • Simple model
        • Collections
        • Complex objects graph
      • Atomic operations
      • Change Tracking Service API
      • Property Metadata for the ChangeTrackingService
      • Handling collection sync
      • Property State
  • Behaviors
    • DataGrid Behaviors
    • Password
    • Generic routed event handler to command behavior
    • Overlay adorner
      • Busy status manager
    • TextBox behaviors:
      • Command
      • Auto select
      • DisableUndoManager (.Net 3.5 only)
  • Markup Extensions
    • Editor binding
    • Auto Command binding
  • How to
    • Get the view of a given view model
    • Bi-directional communication between different windows/views
    • Handle the busy status during async/long running operations
    • Implement a customer improvement program
    • Manage focus
    • Create a splash screen
    • Access view model after view is closed
    • Intercept ViewModels before they are used
  • Upgrade guides
    • Radical Presentation 1.x to Radical 2.x for .NET Core
    • Radical 2.0.0 to Radical 2.1.0
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  1. Concepts
  2. Observers

PropertyObserver

A basic observer, or monitor, in the Radical framework is a PropertyObserver the role of a property observer is to monitor property changes of a class implementing the INotifyPropertyChanged interface. We can monitor single properties:

var monitor = PropertyObserver.For(person)
    .Observe(p => p.FirstName)
    .Observe(p => p.LastName);

monitor.Changed += (s, e) =>
{
    //occurs when one of the properties change.
};

Or we can monitor the entire entity being notified each time a property changes:

var monitor = PropertyObserver.ForAllPropertiesOf(person);
monitor.Changed += (s, e) =>
{
    //occurs when one of the properties change.
};

We can use a monitor to trigger, for example, the CanExecuteChanged event of a ICommand interface implementation:

var monitor = PropertyObserver.ForAllPropertiesOf( person );

DelegateCommand.Create()
    .OnCanExecute(state =>
    {
        //evaluate if the command can be executed.
        return true;
    })
    .OnExecute(state =>
    {
        //execute the command
    })
    .AddMonitor(monitor);

In the above sample each time one of the property of the Person instance changes the command state will be evaluated for execution allowing the command to change its CanExecute state without polling anything but simply waiting to be notified.

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Last updated 3 years ago