When my app boots up it fetches a bunch of jobs using
ref.on('value', snapshot => {
// DO STUFF WITH snapshot.val()
});
I know the .on()listener will fire every time the node changes.
For my app I manage the app state differently depending if the app is booting up OR if it already booted up and the .on() listener is firing because the node UPDATED.
As per the docs:
The listener is triggered once for the initial state of the data and again anytime the data changes.
Is there any way to know, if the .on() is firing because a change to the node has been made or it is the first load?
Thanks!
Related
Do event listeners guarantee that all data ever written to a path will be delivered to the client eventually?
For instance if I have a game client that pushes moves to the same path one after the other will the listening client receive all updates?
What would happen in this situation: client A pushes move 1 to game1/user1/move_data which client B is listening on; client A then immediately pushes another move updating the value at game1/user1/move_data.
Will the listening client be guaranteed to receive all moves pushed?
Currently I have a system that creates a new path per move and then I am calling single listeners on each move as each client reaches that move in it's state. It doesn't seem efficient as if the client A receives the most recent move that client B has made then client A begins listening on a path that doesn't exist yet.
The below quotes are from this link: https://firebase.google.com/docs/database/admin/retrieve-data
"The value event is used to read a static snapshot of the contents at a given database path, as they existed at the time of the read event. It is triggered once with the initial data and again every time the data changes. The event callback is passed a snapshot containing all data at that location, including child data. In the code example above, value returned all of the blog posts in your app. Everytime a new blog post is added, the callback function will return all of the posts."
The part about as they existed at the time of the read event causes me to think that if a listener is on a path then the client will receive all values ever on that path eventually.
There is also this line from the guarantees section which I am struggling to decipher:
"Value events are always triggered last and are guaranteed to contain updates from any other events which occurred before that snapshot was taken."
I am working with a language that does not have a Google based sdk and am asking this question, so I can further assess Firebases' suitability for my uses.
Firebase Realtime Database performs state synchronization. If a client is listening to data in a location, it will receive the state of that data. If there are changes in the data, it will receive the latest state of that data.
...if I have a game client that pushes moves to the same path one after the other will the listening client receive all updates?
If there are multiple updates before the Firebase server has a chance to send the state to a listener, it may skip some intermediate values. So there is no guarantee that your client will see every state change, there is just a guarantee that it will eventually see the latest state.
If you want to ensure that all clients (can) see all state changes, you should store the state changes themselves in the database.
try to this code to get update value from firebase database:-
mFirebaseInstance = FirebaseDatabase.getInstance();
mFirebaseDatabase = mFirebaseInstance.getReference();
mFirebaseDatabase.child("new_title").setValue("Realtime Database");
mFirebaseDatabase.child("new_title").addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
String appTitle = dataSnapshot.getValue().toString();
Log.e("Hey", appTitle);
title.setText(appTitle);
}
#Override
public void onCancelled(DatabaseError error) {
// Failed to read value
Log.e("Hey", "Failed to read app title value.", error.toException());
}
});
We are using MongoDB Realm in our app.
The first time the user is connected to the app, the ProgressNotifcation callback is triggered correctly, and it will work and trigger whenever a new download is coming.
Even if no download is pending, the ProgressNotification callback will be triggered (the Progress object pass in the callback will contain values from the last download) at least once(when creating it). I supposed this is due to the fact that we are downloading the first data set of the user.
But after killing the app and launching it again, the ProgressNotification callback is not triggered anymore until new data are received by the app. And from this point, the callback will be called every time we need it.
It seems that now, the framework needs a first download since the app is launch to make ProgressNotification callback to be triggered every time we need it.
This was working in the previous version of Realm (5.X.X). We just finished the migration to Realm 10 and discover this issue.
I am a bit stuck here, do not know if this is an intended change or a bug on my part. But I am pretty sure this was working in the previous version of the SDK.
Can anyone help me with this? Thanks
Note: this is no more working in both mode : .forCurrentlyOutstandingWork and .reportIndefinitely
Example
self.token = syncSession.addProgressNotification(for: .download, mode: .forCurrentlyOutstandingWork) { progress in
.......Some code........ <- this part of the code is not triggered anymore
}
EDIT - 21/12/2020
For clarification, the token returned contains a value and the .invalidate is not being called.
There is no error in the session and any new download is triggering the callback. After an initial download, everything works as expected. This means that when I add a progressNotifcation later on, the callback is triggered immediately with the progress of the previous download. But if there is not an initial download, the callback is never called.
For the scope, this method is actually in the custom publisher that I created and it is not deallocated.
Realm 10.5.0
iOS 14.3
Do event listeners guarantee that all data ever written to a path will be delivered to the client eventually?
For instance if I have a game client that pushes moves to the same path one after the other will the listening client receive all updates?
What would happen in this situation: client A pushes move 1 to game1/user1/move_data which client B is listening on; client A then immediately pushes another move updating the value at game1/user1/move_data.
Will the listening client be guaranteed to receive all moves pushed?
Currently I have a system that creates a new path per move and then I am calling single listeners on each move as each client reaches that move in it's state. It doesn't seem efficient as if the client A receives the most recent move that client B has made then client A begins listening on a path that doesn't exist yet.
The below quotes are from this link: https://firebase.google.com/docs/database/admin/retrieve-data
"The value event is used to read a static snapshot of the contents at a given database path, as they existed at the time of the read event. It is triggered once with the initial data and again every time the data changes. The event callback is passed a snapshot containing all data at that location, including child data. In the code example above, value returned all of the blog posts in your app. Everytime a new blog post is added, the callback function will return all of the posts."
The part about as they existed at the time of the read event causes me to think that if a listener is on a path then the client will receive all values ever on that path eventually.
There is also this line from the guarantees section which I am struggling to decipher:
"Value events are always triggered last and are guaranteed to contain updates from any other events which occurred before that snapshot was taken."
I am working with a language that does not have a Google based sdk and am asking this question, so I can further assess Firebases' suitability for my uses.
Firebase Realtime Database performs state synchronization. If a client is listening to data in a location, it will receive the state of that data. If there are changes in the data, it will receive the latest state of that data.
...if I have a game client that pushes moves to the same path one after the other will the listening client receive all updates?
If there are multiple updates before the Firebase server has a chance to send the state to a listener, it may skip some intermediate values. So there is no guarantee that your client will see every state change, there is just a guarantee that it will eventually see the latest state.
If you want to ensure that all clients (can) see all state changes, you should store the state changes themselves in the database.
try to this code to get update value from firebase database:-
mFirebaseInstance = FirebaseDatabase.getInstance();
mFirebaseDatabase = mFirebaseInstance.getReference();
mFirebaseDatabase.child("new_title").setValue("Realtime Database");
mFirebaseDatabase.child("new_title").addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
String appTitle = dataSnapshot.getValue().toString();
Log.e("Hey", appTitle);
title.setText(appTitle);
}
#Override
public void onCancelled(DatabaseError error) {
// Failed to read value
Log.e("Hey", "Failed to read app title value.", error.toException());
}
});
i use minishlink/web-push for send pushes. And i make a service worker serviceworker.js for push messages, with push, notificationclick and notificationclose events listener.
To the site where the subscription takes place a have sw.js:
let timeStampInMs = new Date().getTime();
importScripts('https://super-push-site.com/serviceworker.js?ts=' + timeStampInMs);
It works fine.
But i make a new version of service worker and place it on old place (https://super-push-site.com/serviceworker.js).
How to update service worker version of my subscribers without their visit to the site where the subscription takes place?
Before answering your question, I would like to note that it's considered a bad practice to add a cache-buster parameter to your service worker URL, since the browser will already enqueue the new service worker for installation if it's byte-different to the existing service worker. You may read more about this on: The Service Worker Lifecycle
Now, to answer your actual question:
You can manually trigger the update by calling the update() method of your service worker registration, when a push message is received:
self.addEventListener('push', function (event) {
...
event.waitUntil(
Promise.all([
self.registration.showNotification(title, options);
self.registration.update()
])
);
});
You may also want to trigger self.registration.update() only if there actually is a newer version of the service worker available. To do that:
Store the version identifier of your SW in a variable.
Always send the latest SW version identifier within your push message payload.
Compare the two and trigger self.registration.update() if they don't match.
Hope this helps!
Every time the Watch receives a notification (let's say local), either the static long look or the dynamic long look interface is loaded.
However, what I am observing is that every time the corresponding watch app's first interface controller is also getting loaded.
Is it something that other people have also observed?
Every time the Watch receives a notification, the watch app's first interface controller also gets run behind the scenes.
If it really does, how to distinguish when the watch app ran because user opened it and when it ran because there was a notification that came? context in awakeWithContext: is null in both cases.
Yes, I noticed too. It also seems it is in charge to handle the action methods for for local and remote Notification when tap on a button:
handleActionWithIdentifier:forLocalNotification:
I think you can use:
didReceiveRemoteNotification:withCompletion:
or
didReceiveLocalNotification::withCompletion:
to detect when your app is populated from a remote or local notification
As of watchOS 3 you can out exit of awake(withContext:) early in this scenario by inspecting the applicationState of your extension:
override func awake(withContext context: Any?) {
if #available(watchOS 3.0, *) {
if WKExtension.shared().applicationState == .background {
print("Awake with Context in background. Not processing.")
return
}
}
// otherwise, load normally
}