valueChanged

ValueChanged is a common naming convention used in programming to denote a signal, event, or callback that is raised when a value changes. It is used across multiple languages and frameworks to notify interested parties of updates to a property's value or to a control's state.

In practice, ValueChanged is implemented as an event or callback. Subscriber code receives a notification that includes information about the change, often the new value, and sometimes the previous value. For example, in Flutter a common pattern is the typedef ValueChanged<T> = void Function(T value), where onChanged callbacks receive the new value. In .NET and related UI toolkits, a ValueChanged event may be raised on controls such as sliders or numeric inputs when the underlying Value property changes; event data may include old and new values, or simply signal that a change occurred.

ValueChanged is frequently used in user interface code to synchronize UI with user input or model data. It often accompanies data binding, where a change to a source value triggers updates to bound observers, or is used in custom components to expose a simple change handshake to consumers.

Considerations include whether the event should fire on user input only or also on programmatic changes, how to avoid redundant notifications when the value remains the same, and how to handle multithreading or asynchronous observers.

See also: property change notifications, INotifyPropertyChanged, Value, OnValueChanged.