Using single Class in multiple Activities

Question

I implemented a class called WebSocketClient which provides the functionality to open and connect to a websocket, send data through the websocket, etc... Now I want to use this class in my Activities. In order to be informed of incomming messages from the websocket i created a WebsocketListener which can be registered in the WebSocketClient so the activity which would like to communicate through the Websocket would implement this interface and register itself. The problem is, how can I use the WebSocketClient in multiple activities? My first idea was to implement the WebSocketClient class as a Singleton, so in each activity I am able to get the instance of the WebSocketClient via WebSocketClient.getInstance() and register itself as a WebSocketListener. Is this a good way of implementing what i want? So if i am in Activity A i would call WebSocketClient.getInstance().register(this), when i switch to the next Activity B I also have to call WebSocketClient.getInstance().register(this) which would change the current listener to the current active activity. This way i am able to use the WebSocketClient in each activity.

Will this work? Does anybody have a better solution?

kind regards

This sounds ok it's just a matter of implementation now. Are you using the Application class? — Erik, Sep 12 '13 at 12:01

Erik · Accepted Answer · 2013-09-12T22:32:08.467

You could use the Application class and start your WebSocketClient class as a Singleton.

public class WebSocketClientManager implements OnCloseListener {

 private WeakHashMap<? extends BaseUIListener, Integer> uiListenerss;
 private final static WebSocketClientManager instance;
 static {
    instance = new WebSocketClientManager();
 }

 public static WebSocketClientManager getInstance() {
    return instance;
 }

 @Override
   public void onCloseingTheApp() {
   // do stuff
 }

 // methods
  getListeners 
  setListener
}

You could also let the Application class hold all BaseUIListener. And then in all your Activity´s onResume() you do like this:

 Application.getInstance().addUIListener(OnSomeChangedListener.class, this);

Your WebSocketClientManager when it has something to say it will do like this

for (OnSomeChangedListener someChangedListener: Application.getInstance().getUIListeners(OnSomeChangedListener.class))
     someChangedListener.OnSomeChanged("This just happend");

There is a very nice example of this here: xabber Application class

But if my listeners are Activities, what happens if an activity which is not currently active receives an OnSomeChanged event? — Moonlit, Sep 12 '13 at 14:12
You must read [Official doc Android Activity](http://developer.android.com/guide/components/activities.html) It will save you so much headake because it's so intrikat . To answer your question yes it can but that's not what Activities are for and when the Activity has come to onStopped() it is not even attached to the window manager. Use Onresume() end onPause() to register/unregister listeners and get OnSomeChanged when Activity is visible — Erik, Sep 12 '13 at 16:28

score 0 · Answer 2 · edited May 23 '17 at 12:28

If you store your WebSocketClient object in the Application class you would not have to have Singleton. You could just get it from getApplicationContext() method in activities and use its methods as they are.

That being said, if you will implement Singleton, I would suggest using INSTANCE variable in enum instead of getInstance() method. You can find example at following url: What is the best approach for using an Enum as a singleton in Java?

Using single Class in multiple Activities

2 Answers2

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