EventDispatcherIs the center of event distribution, GObject is an EventDispatcher. Each event type corresponds to oneEventListenerTo receive events and call handlers.

For example, write processing logic for a component click:

void aCallback()
//some logic

Bubbling and catching

Some special events, such as mouse / touch events, have the characteristics of passing to the parent component. This passing process is called bubbling. For example, when a finger touches the A component, the A component triggers the TouchBegin event, then the parent component B of the A component triggers the TouchBegin event, and then the parent component C of the B component also triggers the TouchBegin event, and so on until the root of the stage. This design guarantees that all related display objects have the opportunity to handle touch events, not just the topmost display object.

The bubbling process can be interrupted. By calling EventContext.StopPropagation (), the bubbling can be stopped to advance to the parent component.

As can be seen from the bubbling process above, the order of event processing should be: A’s listeners-> B’s listeners-> C’s listeners. There is also a mechanism that allows any object on the link to process events in advance. This is event capture. . Event capture is reversed. For example, in the above example, C captures the event first, then B, and then A. So the complete sequence of all event processing should be:

C’s capture listeners->B’s capture listeners->A’s capture listeners->A’s listeners->B’s listeners->C’s listeners

Capturing delivery chains cannot be aborted, and bubbling delivery chains can be aborted with StopPropagation.
Event capture is designed to allow parent components to inspect events over child and grandchild components.

Not all events have a bubbling design. In non-bubbling events, capture callbacks are better than ordinary callbacks, nothing more, and can be used as a priority feature.

Event callback function

Each event can register one or more callback functions. The function prototype is:

public delegate void EventCallback0();
public delegate void EventCallback1(EventContext context);

The two forms of use are the same, the difference is that there is no parameter or a parameter, just for convenience to write less when you do not need to use EventContext.

There is no way to directly pass custom parameters into the callback function. But it can be achieved indirectly in three ways:

  1. Through global or module variables;
  2. Use lamba expressions, for example:
a.onClick.Add(()=>{ ... });
  1. Put the variable in the data property of the display object. E.g:
a.data = ...;
void aCallback(EventContext context)



EventContext is the parameter type of the callback function.


For keyboard events and mouse / touch events, you can get the relevant data of such events through EventContext.inputEvent.