NavigationListener (navigation-framework 1.0.1 API)

```
public interface NavigationListener
```
An external observer of navigation events.
Registered through Navigator.addNavigationListener(NavigationListener). The callback is delivered at the same time as the corresponding page lifecycle callbacks, once per navigation operation (Navigator.navigateTo(int), Navigator.navigateBack(), Navigator.navigateBackTo(int), Navigator.replaceWith(int)). A navigation requested from onNavigation(ej.navigation.Page, ej.navigation.Page) is deferred and performed once the navigation in progress is finished.
onNavigation(ej.navigation.Page, ej.navigation.Page) receives the Page instances so the "no page exited on the first navigation" case stays expressible as a null; an application that needs keys can call Navigator.getActiveKey().

Since:

0.2.0

Method Summary

All Methods Instance Methods Abstract Methods
Modifier and Type	Method	Description
`void`	`onNavigation(Page exitedPage, Page enteredPage)`	Notifies that the active page has changed from `exitedPage` to `enteredPage`.

- Method Detail
  - onNavigation
```
void onNavigation(@Nullable
                  Page exitedPage,
                  Page enteredPage)
```
    Notifies that the active page has changed from exitedPage to enteredPage.
    Fires once per navigation. On the first navigation no page is exited, so exitedPage is null; on every navigation thereafter it is the page that was active before.
    
    Parameters:
    
    exitedPage - the page that was active before, or null when the entered page is the first page ever shown.
    
    enteredPage - the page that is now active.