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Connecting Bean Events

The process of connecting events is, from the user's point of view, similar to binding bean properties, e.g., connecting bean events is done in five steps. However, the underlying mechanism is much different.

1.

Selecting the source. As described in Section 1, selecting a new current-bean will change the BeanBoxFrame's menu bar based on the characteristics of the selected bean. In the Edit menu item, just under the Events item, there is a submenu that consists of all the event names the selected bean can announce. This is obtained using introspection. Under every event name, there is another submenu that lists all method names of the listener interface for the selected event.

2.

Selecting a receiving method from the event listener interface. When the user clicks on one of the listener's methods, BeanBox responds to that ActionEvent by calling its doEventHookup() method. Based on the event's name and the name of the listener's method, that method will then find the EventSetDescriptor of the selected event and the Method object for the named method.

3.

Selecting the target. After the user selects an event, BeanBox waits for the user to click with the mouse on a target bean. The selected bean is the bean that will eventually respond to the event fired by the source bean via the selected listener's method.

4.

Selecting the method to be invoked. Once the target bean has been selected, the BeanBox will create a new instance of EventTargetDialog, passing to it the wrappers of the source and the target beans, the event descriptor, and the listener's method. The EventTargetDialog will then introspect the target bean in hopes of finding a method that either matches the event listener method or has no arguments and no return value. If any matching methods are found, it will make a list and let the user choose one. The chosen method will be the one that is invoked on the target bean in response to the source bean announcing an event on the selected listener method.

5.

Making a connection. When the user selects a target method, all the needed information for making the connection is available, and the EventTargetDialog calls the hookup() method of HookupManager, which will actually generate the connection. The connection is established by generating a new adapter class that implements the listener interface of the selected event. The implementation of the listener methods is trivial. In the selected method case, it calls the selected method in the target bean, and, in any other case, the method body is left empty. HookupManager also takes care of compiling on the fly the newly created adapter class, creating a new instance of it, setting the target object to that instance, and registering it with the source bean. Creating a new class is unavoidable because the listener can be of any user defined type, unlike in the binding-properties case where the listener is always of the PropertyChangeListener type.

NU-CCS-99-04.ps [ Readme | Copyright | Tutorial | Download | Feedback ]