Activity (GWT Javadoc)

All Known Implementing Classes:

AbstractActivity
```
public interface Activity
```
Implemented by objects that control a piece of user interface, with a life cycle managed by an ActivityManager, in response to PlaceChangeEvent events as the user navigates through the app.

Method Summary

All Methods Instance Methods Abstract Methods
Modifier and Type	Method	Description
`java.lang.String`	`mayStop()`	Called when the user is trying to navigate away from this activity.
`void`	`onCancel()`	Called when `start(com.google.gwt.user.client.ui.AcceptsOneWidget, com.google.gwt.event.shared.EventBus)` has not yet replied to its callback, but the user has lost interest.
`void`	`onStop()`	Called when the Activity's widget has been removed from view.
`void`	`start(AcceptsOneWidget panel, EventBus eventBus)`	Called when the Activity should ready its widget for the user.

- Method Detail
  - mayStop
```
java.lang.String mayStop()
```
    Called when the user is trying to navigate away from this activity.
    
    Returns:
    
    A message to display to the user, e.g. to warn of unsaved work, or null to say nothing
  - onCancel
```
void onCancel()
```
    Called when start(com.google.gwt.user.client.ui.AcceptsOneWidget, com.google.gwt.event.shared.EventBus) has not yet replied to its callback, but the user has lost interest.
  - onStop
```
void onStop()
```
    Called when the Activity's widget has been removed from view. All event handlers it registered will have been removed before this method is called.
  - start
```
void start(AcceptsOneWidget panel,
           EventBus eventBus)
```
    Called when the Activity should ready its widget for the user. When the widget is ready (typically after an RPC response has been received), receiver should present it by calling AcceptsOneWidget.setWidget(com.google.gwt.user.client.ui.IsWidget) on the given panel.
    Any handlers attached to the provided event bus will be de-registered when the activity is stopped, so activities will rarely need to hold on to the HandlerRegistration instances returned by EventBus.addHandler(com.google.web.bindery.event.shared.Event.Type<H>, H).
    
    Parameters:
    
    panel - the panel to display this activity's widget when it is ready
    
    eventBus - the event bus