de.saxsys.mvvmfx.utils.notifications

Class WeakNotificationObserver

java.lang.Object

de.saxsys.mvvmfx.utils.notifications.WeakNotificationObserver

All Implemented Interfaces:

NotificationObserver

public final class WeakNotificationObserver
extends Object
implements NotificationObserver

This class is a wrapper of a NotificationObserver that only holds a weak reference to the observer.

When using normal NotificationObserver in combination with the global NotificationObserver the notification center will hold a reference to the observer as long as it isn't unregistered. The observer itself will most likely hold a reference to the parent class which can prevent the parent class from being garbage collected. In many use cases this is not a problem but in some situations this can cause memory leaks.

For such situations this class can be used as a Wrapper around the normal notification observer. The usage should look like this:

 public class MyClass {

     private NotificationObserver observer;

     ...

     public void someMethod() {
         observer = (key, payload) -> {
           // do something when observer is called.

         };

         notificationCenter.subscribe("some_topic", new WeakNotificationObserver(observer));
     }
 }
 

The example shows the following steps:

• Create a field for your observer of type NotificationObserver
• Create an instance of your observer, for example as a lambda.
• subscribe to a topic by creating a new instance of WeakNotificationObserver and pass the normal observer as constructor argument

It's important to hold a hard reference to the normal observer in your class. This can be done by creating a field for the observer. This way you prevent the observer from being garbage collected to early. Creating a local variable in the body of a method will not work!

Using the pattern mentioned above will:

• prevent the observer from being garbage collected to early
• allow the garbage collector to collect the parent class as soon as it isn't references in other places

Author:

manuel.mauky

Constructor Summary

Constructors

Constructor and Description
WeakNotificationObserver(NotificationObserver notificationObserver)

Method Summary

Modifier and Type	Method and Description
void	receivedNotification(String key, Object... payload) Handle the Notification which is passed by the NotificationCenter.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

WeakNotificationObserver

public WeakNotificationObserver(NotificationObserver notificationObserver)

Method Detail

receivedNotification

public void receivedNotification(String key,
                                 Object... payload)

Description copied from interface: NotificationObserver

Handle the Notification which is passed by the NotificationCenter. An @Object[] could be shipped.

Specified by:

receivedNotification in interface NotificationObserver

Parameters:

key - notification name

payload - which are passed