PropertyChanged

PropertyChanged refers to a notification mechanism used to signal that the value of a property has changed. It is commonly employed in data binding and reactive UI patterns, allowing observers such as user interfaces or other components to refresh dependent values when underlying data changes.

In the .NET ecosystem, the most widely used form is the INotifyPropertyChanged interface. It defines a PropertyChanged event that is raised whenever a property value is updated. Classes implementing this interface typically provide a method (often called OnPropertyChanged) to raise the event after changing a property's backing field. This pattern enables automatic UI updates in frameworks like WPF, UWP, Xamarin.Forms, and MAUI, supporting the Model-View-ViewModel (MVVM) design.

Typical implementation concerns include using a backing field for each property, checking for actual value changes before raising the event, and ensuring the event is raised after the value is updated. Modern languages offer conveniences such as automatic property change notification using attributes or features like CallerMemberName to avoid hard-coded property names. Thread-safety and proper subscription management are important to prevent race conditions and memory leaks.

Other platforms have analogous mechanisms. JavaBeans uses PropertyChangeListener with a PropertyChangeSupport helper, while JavaFX provides observable properties. Similar concepts exist in Swift's Key-Value Observing and in various reactive programming libraries that notify observers of changes.

Overall, PropertyChanged supports decoupled data models and responsive user interfaces, at the cost of added boilerplate and careful design to maintain performance and reliability. See also data binding, MVVM, and observable patterns.