ViewChangeListener (vaadin-server 8.27.0 API)

All Superinterfaces:

Serializable

Functional Interface:

This is a functional interface and can therefore be used as the assignment target for a lambda expression or method reference.
```
@FunctionalInterface
public interface ViewChangeListener
extends Serializable
```
Interface for listening to View changes before and after they occur.
Implementations of this interface can also block navigation between views before it is performed (using beforeViewChange(ViewChangeEvent)).
The interface contains two methods beforeViewChange(ViewChangeEvent) and afterViewChange(ViewChangeEvent). The latter one has default empty implementation.

Since:

7.0

Author:

Vaadin Ltd

Nested Class Summary

Nested Classes
Modifier and Type Interface Description

static class ViewChangeListener.ViewChangeEvent
Event received by the listener for attempted and executed view changes.

Method Summary

All Methods Instance Methods Abstract Methods Default Methods
Modifier and Type	Method	Description
`default void`	`afterViewChange(ViewChangeListener.ViewChangeEvent event)`	Invoked after the view is changed.
`boolean`	`beforeViewChange(ViewChangeListener.ViewChangeEvent event)`	Invoked before the view is changed.

- Method Detail
  - beforeViewChange
```
boolean beforeViewChange(ViewChangeListener.ViewChangeEvent event)
```
    Invoked before the view is changed.
    This method may e.g. open a "save" dialog or question about the change, which may re-initiate the navigation operation after user action.
    If this listener does not want to block the view change (e.g. does not know the view in question), it should return true. If any listener returns false, the view change is not allowed and afterViewChange() methods are not called.
    
    Parameters:
    
    event - view change event
    
    Returns:
    
    true if the view change should be allowed or this listener does not care about the view change, false to block the change
  - afterViewChange
```
default void afterViewChange(ViewChangeListener.ViewChangeEvent event)
```
    Invoked after the view is changed. If a beforeViewChange method blocked the view change, this method is not called. Be careful of unbounded recursion if you decide to change the view again in the listener.
    By default it does nothing. Override it in your listener if you need this functionality.
    
    Parameters:
    
    event - view change event