# CallbackEventHandler

> Interface for classes capable of having callbacks to handle events.

## Definition

* **Type:** Class
* **Namespace:** [UnityEngine.UIElements](/engine/6000.7/script-reference/unityengine/uielements.md)
* **Assembly:** UnityEngine.UIElementsModule
* **Implements:** [IEventHandler](/engine/6000.7/script-reference/unityengine/uielements/ieventhandler.md)

```csharp
public abstract class CallbackEventHandler : IEventHandler
```

## Methods

| Method                                                                                                                                            | Description                                                                                                                                                                                                              |
| ------------------------------------------------------------------------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |
| [HandleEventBubbleUp](/engine/6000.7/script-reference/unityengine/uielements/callbackeventhandler/handleeventbubbleup.md)                         | Executes logic on this element during the BubbleUp phase, immediately before this element's BubbleUp callbacks. Calling StopPropagation will prevent further invocations of this method along the propagation path.      |
| [HandleEventTrickleDown](/engine/6000.7/script-reference/unityengine/uielements/callbackeventhandler/handleeventtrickledown.md)                   | Executes logic on this element during the TrickleDown phase, immediately after this element's TrickleDown callbacks. Calling StopPropagation will prevent further invocations of this method along the propagation path. |
| [HasBubbleUpHandlers](/engine/6000.7/script-reference/unityengine/uielements/callbackeventhandler/hasbubbleuphandlers.md)                         | Return true if event handlers for the event propagation BubbleUp phase have been attached to this object.                                                                                                                |
| [HasTrickleDownHandlers](/engine/6000.7/script-reference/unityengine/uielements/callbackeventhandler/hastrickledownhandlers.md)                   | Returns true if event handlers, for the event propagation TrickleDown phase, are attached to this object.                                                                                                                |
| [NotifyPropertyChanged](/engine/6000.7/script-reference/unityengine/uielements/callbackeventhandler/notifypropertychanged.md)                     | Informs the data binding system that a property of a control has changed.                                                                                                                                                |
| [RegisterCallback](/engine/6000.7/script-reference/unityengine/uielements/callbackeventhandler/registercallback.md)                               | Adds an event handler to the instance.                                                                                                                                                                                   |
| [RegisterCallbackOnce](/engine/6000.7/script-reference/unityengine/uielements/callbackeventhandler/registercallbackonce.md)                       | Adds an event handler to the instance. The event handler is automatically unregistered after it has been invoked exactly once.                                                                                           |
| [SendEvent](/engine/6000.7/script-reference/unityengine/uielements/callbackeventhandler/sendevent.md)                                             | Sends an event to the event handler.                                                                                                                                                                                     |
| [UnregisterAllRemovableCallbacks](/engine/6000.7/script-reference/unityengine/uielements/callbackeventhandler/unregisterallremovablecallbacks.md) | Removes all callbacks registered with [CallbackOptions.Removable](/engine/6000.7/script-reference/unityengine/uielements/callbackoptions/removable.md) from the instance.                                                |
| [UnregisterCallback](/engine/6000.7/script-reference/unityengine/uielements/callbackeventhandler/unregistercallback.md)                           | Remove callback from the instance.                                                                                                                                                                                       |