PropertyObserver

PropertyObserver

The PropertyObserver is a wrapper class that makes it easier to monitor INotifyPropertyChanged events on child objects. It provides a type-safe way to register specific actions in response to specific property changes.

Usage

You pass the specific object that implements INotifyPropertyChanged into the constructor and keep a reference to this object. You then register handlers for property changes using the RegisterHandler method. When you are finished, you can Dispose the property observer to remove all your handlers.

The object supports a fluent syntax where you can chain registrations together which makes it a single line of code to create and then wire up any property change notifications.

Properties

• Source : The object being monitored. It must implement INotifyPropertyChanged.

Methods

• RegisterHandler : registers a delegate to be called when a specific property is changed.
• UnregisterHandler : unregisters a specific property handler on the source object.
• Dispose : removes all property notification handlers on the source object.

Example

public class ParentViewModel : SimpleViewModel
{
    ChildVM childVM;
    PropertyObserver<ChildVM> childObserver;

    // Create a nice title from the child.
    public string Title => $"{childVM.Name} is {childVM.Age} years old.";

    public ParentViewModel(ChildVM child)
    {
       childVM = child;
       
       // Monitor INPC on the child
       childObserver = new PropertyObserver<ChildVM>(child)
            // Register two handlers - both invalidate our Title property.
           .RegisterHandler(c => c.Name, RaisePropertyChanged(nameof(Title))
           .RegisterHandler(c => c.Age, RaisePropertyChanged(nameof(Title));
   }
   ...
}