Android equivalent to NSNotificationCenter
You could try this: http://developer.android.com/reference/java/util/Observer.html
The best equivalent I found is LocalBroadcastManager which is part of the Android Support Package.
From the LocalBroadcastManager documentation:
Helper to register for and send broadcasts of Intents to local objects within your process. This is has a number of advantages over sending global broadcasts with sendBroadcast(Intent):
- You know that the data you are broadcasting won't leave your app, so don't need to worry about leaking private data.
- It is not possible for other applications to send these broadcasts to your app, so you don't need to worry about having security holes they can exploit.
- It is more efficient than sending a global broadcast through the system.
When using this, you can say that an Intent
is an equivalent to an NSNotification
. Here is an example:
ReceiverActivity.java
An activity that watches for notifications for the event named "custom-event-name"
.
@Override
public void onCreate(Bundle savedInstanceState) {
...
// Register to receive messages.
// This is just like [[NSNotificationCenter defaultCenter] addObserver:...]
// We are registering an observer (mMessageReceiver) to receive Intents
// with actions named "custom-event-name".
LocalBroadcastManager.getInstance(this).registerReceiver(mMessageReceiver,
new IntentFilter("custom-event-name"));
}
// Our handler for received Intents. This will be called whenever an Intent
// with an action named "custom-event-name" is broadcasted.
private BroadcastReceiver mMessageReceiver = new BroadcastReceiver() {
@Override
public void onReceive(Context context, Intent intent) {
// Get extra data included in the Intent
String message = intent.getStringExtra("message");
Log.d("receiver", "Got message: " + message);
}
};
@Override
protected void onDestroy() {
// Unregister since the activity is about to be closed.
// This is somewhat like [[NSNotificationCenter defaultCenter] removeObserver:name:object:]
LocalBroadcastManager.getInstance(this).unregisterReceiver(mMessageReceiver);
super.onDestroy();
}
SenderActivity.java
The second activity that sends/broadcasts notifications.
@Override
public void onCreate(Bundle savedInstanceState) {
...
// Every time a button is clicked, we want to broadcast a notification.
findViewById(R.id.button_send).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
sendMessage();
}
});
}
// Send an Intent with an action named "custom-event-name". The Intent sent should
// be received by the ReceiverActivity.
private void sendMessage() {
Log.d("sender", "Broadcasting message");
Intent intent = new Intent("custom-event-name");
// You can also include some extra data.
intent.putExtra("message", "This is my message!");
LocalBroadcastManager.getInstance(this).sendBroadcast(intent);
}
With the code above, every time the button R.id.button_send
is clicked, an Intent is broadcasted and is received by mMessageReceiver
in ReceiverActivity
.
The debug output should look like this:
01-16 10:35:42.413: D/sender(356): Broadcasting message
01-16 10:35:42.421: D/receiver(356): Got message: This is my message!
Here is something similar to @Shiki answer, but from the angle of iOS developers and Notification center.
First create some kind of NotificationCenter service:
public class NotificationCenter {
public static void addObserver(Context context, NotificationType notification, BroadcastReceiver responseHandler) {
LocalBroadcastManager.getInstance(context).registerReceiver(responseHandler, new IntentFilter(notification.name()));
}
public static void removeObserver(Context context, BroadcastReceiver responseHandler) {
LocalBroadcastManager.getInstance(context).unregisterReceiver(responseHandler);
}
public static void postNotification(Context context, NotificationType notification, HashMap<String, String> params) {
Intent intent = new Intent(notification.name());
// insert parameters if needed
for(Map.Entry<String, String> entry : params.entrySet()) {
String key = entry.getKey();
String value = entry.getValue();
intent.putExtra(key, value);
}
LocalBroadcastManager.getInstance(context).sendBroadcast(intent);
}
}
Then, you will also need some enum type to be secure of mistakes in coding with strings - (NotificationType):
public enum NotificationType {
LoginResponse;
// Others
}
Here is usage(add/remove observers) for example in activities:
public class LoginActivity extends AppCompatActivity{
private BroadcastReceiver loginResponseReceiver = new BroadcastReceiver() {
@Override
public void onReceive(Context context, Intent intent) {
// do what you need to do with parameters that you sent with notification
//here is example how to get parameter "isSuccess" that is sent with notification
Boolean result = Boolean.valueOf(intent.getStringExtra("isSuccess"));
}
};
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_login);
//subscribe to notifications listener in onCreate of activity
NotificationCenter.addObserver(this, NotificationType.LoginResponse, loginResponseReceiver);
}
@Override
protected void onDestroy() {
// Don't forget to unsubscribe from notifications listener
NotificationCenter.removeObserver(this, loginResponseReceiver);
super.onDestroy();
}
}
and here is finally how we post notification to NotificationCenter from some callback or rest service or whatever:
public void loginService(final Context context, String username, String password) {
//do some async work, or rest call etc.
//...
//on response, when we want to trigger and send notification that our job is finished
HashMap<String,String> params = new HashMap<String, String>();
params.put("isSuccess", String.valueOf(false));
NotificationCenter.postNotification(context, NotificationType.LoginResponse, params);
}
that's it, cheers!
I found that the usage of EventBus of Guava lib is the simplest way for publish-subscribe-style communication between components without requiring the components to explicitly register with one another
see their sample on https://code.google.com/p/guava-libraries/wiki/EventBusExplained
// Class is typically registered by the container.
class EventBusChangeRecorder {
@Subscribe public void recordCustomerChange(ChangeEvent e) {
recordChange(e.getChange());
}
// somewhere during initialization
eventBus.register(this);
}
// much later
public void changeCustomer() {
eventBus.post(new ChangeEvent("bla bla") );
}
you can add this lib simply on Android Studio by adding a dependency to your build.gradle:
compile 'com.google.guava:guava:17.0'