Android Custom Event Listener

public class CustomView extends View(){
OnCustomEventListener mListener;
:
://some code
:
:

Create an interface that will be implemented by your activity:

public interface OnCustomEventListener {
    void onEvent();
}

public void setCustomEventListener(OnCustomEventListener eventListener) {
    mListener = eventListener;
}

Now you need to know when the event is actually occurring. For example when the user touches a point on screen, override onTouchEvent method:

onTouchEvent(MotionEvent ev) {
    if (ev.getAction==MotionEvent.ACTION_DOWN) {
        if(mListener!=null) 
            mListener.onEvent();
    }
}

Similarly, you can create a specific event that you want. (examples could be touch down, wait for exactly 2 seconds and release- you would need to do some logic inside touch event).

In your activity, you can use the customView object to set an eventListener as such:

 customView.setCustomEventListener(new OnCustomEventListener() {
    public void onEvent() {
        //do whatever you want to do when the event is performed.
    }
 });

Custom event listener on Android app

Define a callback interface

        public interface NewsUpdateListener 
        {
            void onNewsUpdate(<News data to be passed>);
        }

Provide a registration facility on the background thread which gets the RSS feed

    class <Background processing class name> 
    {
    ....
        ArrayList<NewsUpdateListener> listeners = new ArrayList<NewsUpdateListener> ();
    .... 
        public void setOnNewsUpdateListener (NewsUpdateListener listener) 
        {
            // Store the listener object
            this.listeners.add(listener);
        }
    ....
    }

Fire the callback when news is available

....
for (listener : listeners) 
{
    listener.onNewsUpdate(<News data to be passed>);
}
....

....
    <class <Background processing class object>.registerListener
(
    new OnNewsUpdateListener() {
        onNewsUpdate(<News Data>) {
            // process news data
            runOnUIThread(new Runnable() {
                public void run() {
                    // refresh list view
                }
            }
        }
}
....

Java - Create a Custom event and listener

So I made a minimal example maybe that will help you:

You need an interface for your listener:

public interface MyEventListener
{
    public void onMyEvent();
}

Then for your String you need some wrapper class that also handles your events

public class EventString
{
    private String                  myString;

    private List<MyEventListener>   eventListeners;

    public EventString(String myString)
    {
        this.myString = myString;
        this.eventListeners = new ArrayList<MyEventListener>();
    }

    public void addMyEventListener(MyEventListener evtListener)
    {
        this.eventListeners.add(evtListener);
    }

    public void setValue(String val)
    {
        myString = val;

        if (val.equals("hello world"))
        {
            eventListeners.forEach((el) -> el.onMyEvent());
        }
    }
}

You see that the myString field is private and only accessible using the setValue method. This is so we can see when our event condition triggers.

And then you only need some implementation of this, such as:

EventString temp = new EventString("test");

temp.addMyEventListener(() -> {
    System.out.println("hello world detected");
});

temp.setValue("hello world");

Android custom view event listeners not working properly without static reference

In your implementation there are two instances of your custom compound view comes into play, one is in the layout (activity layout) and other one is explicitly created one in the activity onCreate method.

barcodeScannerView = new BarcodeScannerView(this);
barcodeScannerView.setOnScannerListener(this);

You have set the listener to the explicitly created one which doesn't have clue about view used in the layout, simply they are two instances. You should use the instance created (inflated) in the xml as follows.

@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main_activity);

    barcodeScannerView = (BarcodeScannerView) findViewById(R.id.barcode_scanner);
    barcodeScannerView.setOnScannerListener(this);
}

barcode_scanner should be the id you have given to the compound view used in the activity layout.

How do I set a Java library's custom event listener in Kotlin?

You can just paste the code in Android Studio and it will suggest to you to convert it to Kotlin code

The same code in Kotlin will be like this

val menu = findViewById<CircleMenuView>(R.id.circle_menu)
menu.setEventListener(object : CircleMenuView.EventListener {
    override fun onMenuOpenAnimationStart(view : CircleMenuView) {
        Log.d("D", "onMenuOpenAnimationStart");
    }
})

How to define custom events and event listeners in Android?

Use Broadcast Intents to notify listeners of system or application/custom events..

send a Broadcast using sendBroadcast method whenever your custom event occurs..

Intent intent = new Intent(NEW_Intent);
intent.putExtra(“Test”,Test1);
sendBroadcast(intent);

To create a new Broadcast Receiver(which will listen to your event/broadcast), extend the BroadcastReceiver class and override the onReceive event handler.The onReceive method will be executed when a Broadcast Intent is received that matches the Intent Filter used to register the receiver.

//in xml

<receiver android:name=”.ReceiverName”>
<intent-filter>
<action android:name=”com.paad.action.NEW_INTENT”/>
</intent-filter>
</receiver>

//in code..

IntentFilter filter = new IntentFilter(NEW_INTENT);
ReceiverName r = new ReceiverName();
registerReceiver(r, filter);

using custom event listener java

MainActivity.locationListeners is an instance member and cannot be accessed statically like you are currently trying to do in WeatherDbAccess.

What you should do instead since WeatherDBAccess is a singleton is register and unregister it as a locationListener from within MainActivity. It should be in the same life cycle callback methods you are registering and unregistering the LocationListener.

Since you aren't showing that code lets assume it is in onResume() and onPause() but you can put the add and remove methods wherever they really belong.

@Override
public void onResume() {
    super.onResume();
    locationListeners.add(WeatherDBAccess.Instance());
}

@Override
public void onPause() {
    super.onPause();
    locationListeners.remove(WeatherDBAccess.Instance());
}

Android Custom Event Listener