I am trying for a while now to implement this flow: When user adds some files on server app, notification should trigger and send from server to FCM and that from there to pass message saying something like: 'New file has been added'.
Basically I want to inform mobile device user that something on server has been changed.
I have tried many things, but nothing seems to work as I would expect, at least.
On the mobile side I have set up Firebase inside my Xamarin.Android project, and when I am sending notifications directly from Firebase console, I get notifications, and everything is good.
But I don't want to send notifications via Firebase console, I would rather send notification from server (which is ASP.NET MVC project) to Firebase console and then pass it from there to android device.
My first question would be: Has anybody got an idea how can I inform web app about device_id? Is there some way that android device send this information on server? And maybe from there I can store that data and update it occasionally, since it is basically a refresh token.
My second problem is this: Even when I hard code current device_id of an active android device and try to send a message from server whit this code:
public class FirebaseService : IFirebaseService
{
public void SendMessageToClientApplication(string message, string serverApiKey, string senderId, string deviceId)
{
AndroidFCMPushNotificationStatus result = new AndroidFCMPushNotificationStatus();
try
{
result.Successful = false;
result.Error = null;
deviceId = "eMk6mD8P8Dc:APA91bG5Lmqn4Hwb4RZJ1Mkdl8Rf_uYQsQCEfDJK334tzSvIGzdao7o2X6VmtcTEp_Li0mG8iUoUT7-_RnZxQKocHosZwx6ITWdpmQyCwUv60IIIy0vxNlEaccT6RqK6c-cE1C6I3FTT";
var value = message;
WebRequest tRequest = WebRequest.Create("https://fcm.googleapis.com/fcm/send");
tRequest.Method = "post";
tRequest.ContentType = "application/x-www-form-urlencoded;charset=UTF-8";
tRequest.Headers.Add(string.Format("Authorization: key={0}", serverApiKey));
tRequest.Headers.Add(string.Format("Sender: id={0}", senderId));
string postData = "collapse_key=score_update&time_to_live=108&delay_while_idle=1&data.message="
+ value + "&data.time=" + DateTime.Now.ToString() + "®istration_id=" + deviceId + "";
Byte[] byteArray = Encoding.UTF8.GetBytes(postData);
tRequest.ContentLength = byteArray.Length;
using (Stream dataStream = tRequest.GetRequestStream())
{
dataStream.Write(byteArray, 0, byteArray.Length);
using (WebResponse tResponse = tRequest.GetResponse())
{
using (Stream dataStreamResponse = tResponse.GetResponseStream())
{
using (StreamReader tReader = new StreamReader(dataStreamResponse))
{
String sResponseFromServer = tReader.ReadToEnd();
result.Response = sResponseFromServer;
}
}
}
}
}
catch (Exception ex)
{
result.Successful = false;
result.Response = null;
result.Error = ex;
}
}
}
I get nothing both in Firebase console and of course nothing on device as well.
I have tried to implement Firebase web as javascript on my server app like this:
<script>
var config = {
apiKey: "mykey",
authDomain: "myauthdomain",
databaseURL: "mydatabaseurl",
projectId: "myprojectid",
storageBucket: "mystoragebucket",
messagingSenderId: "mysenderid"
};
window.onload = function () {
firebase.initializeApp(config);
const messaging = firebase.messaging();
messaging.requestPermission()
.then(function () {
console.log('Notification permission granted.');
return messaging.getToken()
})
.then(function (token) {
console.log(token);
})
.catch(function (err) {
console.log('Unable to get permission to notify.', err);
});
messaging.onMessage(function (payload) {
console.log('onMessage: ', payload);
});
}
</script>
But this code gets some kind of a different device_id(aka token), probably one generated for that server machine.
Does anybody has experience with sending device_id to server app and from there sending notification message to Firebase console? I would appreciate some code examples, tutorials or anything that can help, since I was unable to find something useful during my google search.
My first question would be: Has anybody got an idea how can I inform web app about device_id?
The most common approach is to store the list of device tokens (each device that uses FCM has such a token) in a database, such as the Firebase Database. There is an example of this in the Cloud Functions for Firebase documentation. In this example the devices receiving the messages are web pages, but the approach is the same for iOS and Android.
I also recommend reading Sending notifications between Android devices with Firebase Database and Cloud Messaging. In this article, instead of sending to a device token, each user subscribes to a topic. That prevents having to manage the device tokens in your code.
After searching the docs I could not find any info on how to send device to device messages using FCM without the use of an external server.
For example, if I was creating a chat application I would need to send push notifications to users about unread messages since they won't be online all the time and I can't have a persistent service in the background that would always be connected to the real time database because that would be too resource heavy.
So how would I send a push notification to a user "A" when a certain user "B" sends him/her a chat message? Do I need an external server for this or can it be done with just Firebase servers?
UPDATE: It is now possible to use firebase cloud functions as the server for handling push notifications. Check out their documentation here
============
According to the docs you must implement a server for handling push notifications in device to device communication.
Before you can write client apps that use Firebase Cloud Messaging, you must have an app server that meets the following criteria:
...
You'll need to decide which FCM connection server protocol(s) you want to use to enable your app server to interact with FCM connection servers. Note that if you want to use upstream messaging from your client applications, you must use XMPP. For a more detailed discussion of this, see Choosing an FCM Connection Server Protocol.
If you only need to send basic notifications to your users from the server. You can use their serverless solution, Firebase Notifications.
See a comparison here between FCM and Firebase Notifications:
https://firebase.google.com/support/faq/#messaging-difference
Making a HTTP POST request with the link https://fcm.googleapis.com/fcm/send with required header and data helped me. In the below code snippet
Constants.LEGACY_SERVER_KEY is a local class variable, you can find this at your Firebase Project Settings->Cloud Messaging->Legacy Server key. You need to pass device registration token i.e. regToken in below code snippet referenced HERE.
At last you need okhttp library dependency in order to get this snippet work.
public static final MediaType JSON
= MediaType.parse("application/json; charset=utf-8");
private void sendNotification(final String regToken) {
new AsyncTask<Void,Void,Void>(){
#Override
protected Void doInBackground(Void... params) {
try {
OkHttpClient client = new OkHttpClient();
JSONObject json=new JSONObject();
JSONObject dataJson=new JSONObject();
dataJson.put("body","Hi this is sent from device to device");
dataJson.put("title","dummy title");
json.put("notification",dataJson);
json.put("to",regToken);
RequestBody body = RequestBody.create(JSON, json.toString());
Request request = new Request.Builder()
.header("Authorization","key="+Constants.LEGACY_SERVER_KEY)
.url("https://fcm.googleapis.com/fcm/send")
.post(body)
.build();
Response response = client.newCall(request).execute();
String finalResponse = response.body().string();
}catch (Exception e){
//Log.d(TAG,e+"");
}
return null;
}
}.execute();
}
further if you want to send message to a particular topic, replace regToken in json like this
json.put("to","/topics/foo-bar")
and don't forget to add INTERNET permission in your AndroidManifest.xml.
IMPORTANT : - Using above code means your server key resides in the client application. That is dangerous as someone can dig into your application and get the server key to send malicious notifications to your users.
You can do it using Volly Jsonobject request....
follow this Steps first:
1 copy legacy server key and store it as Legacy_SERVER_KEY
Legacy Server key
you can see in picture how to get
2 You need Volley dependency
compile 'com.mcxiaoke.volley:library:1.0.19'
Code for send Push:-
private void sendFCMPush() {
String Legacy_SERVER_KEY = YOUR_Legacy_SERVER_KEY;
String msg = "this is test message,.,,.,.";
String title = "my title";
String token = FCM_RECEIVER_TOKEN;
JSONObject obj = null;
JSONObject objData = null;
JSONObject dataobjData = null;
try {
obj = new JSONObject();
objData = new JSONObject();
objData.put("body", msg);
objData.put("title", title);
objData.put("sound", "default");
objData.put("icon", "icon_name"); // icon_name image must be there in drawable
objData.put("tag", token);
objData.put("priority", "high");
dataobjData = new JSONObject();
dataobjData.put("text", msg);
dataobjData.put("title", title);
obj.put("to", token);
//obj.put("priority", "high");
obj.put("notification", objData);
obj.put("data", dataobjData);
Log.e("!_#rj#_##_PASS:>", obj.toString());
} catch (JSONException e) {
e.printStackTrace();
}
JsonObjectRequest jsObjRequest = new JsonObjectRequest(Request.Method.POST, Constants.FCM_PUSH_URL, obj,
new Response.Listener<JSONObject>() {
#Override
public void onResponse(JSONObject response) {
Log.e("!_##_SUCESS", response + "");
}
},
new Response.ErrorListener() {
#Override
public void onErrorResponse(VolleyError error) {
Log.e("!_##_Errors--", error + "");
}
}) {
#Override
public Map<String, String> getHeaders() throws AuthFailureError {
Map<String, String> params = new HashMap<String, String>();
params.put("Authorization", "key=" + Legacy_SERVER_KEY);
params.put("Content-Type", "application/json");
return params;
}
};
RequestQueue requestQueue = Volley.newRequestQueue(this);
int socketTimeout = 1000 * 60;// 60 seconds
RetryPolicy policy = new DefaultRetryPolicy(socketTimeout, DefaultRetryPolicy.DEFAULT_MAX_RETRIES, DefaultRetryPolicy.DEFAULT_BACKOFF_MULT);
jsObjRequest.setRetryPolicy(policy);
requestQueue.add(jsObjRequest);
}
Just Call sendFCMPush();
1) subscribe an identical topic name, for example:
ClientA.subcribe("to/topic_users_channel")
ClientB.subcribe("to/topic_users_channel")
2) send messages inside the application
GoogleFirebase : How-to send topic messages
Yes, it's possible to do it without any server. You can create a device group client side and then you exchange messages in the group. However there are limitations:
You have to use the same Google account on the devices
You can't send high priority messages
Reference: Firebase doc See the section "Managing device groups on Android client apps"
Google Cloud Functions make it now possible send push notifications from device-to-device without an app server.
I have made cloud function which is trigger when new message is added in database
It is node.js code
'use strict';
const functions = require('firebase-functions');
const admin = require('firebase-admin'); admin.initializeApp();
exports.sendNotification = functions.database.ref('/conversations/{chatLocation}/{messageLocation}')
.onCreate((snapshot, context) => {
// Grab the current value of what was written to the Realtime Database.
const original = snapshot.val();
const toIDUser = original.toID;
const isGroupChat = original.isGroupChat;
if (isGroupChat) {
const tokenss = admin.database().ref(`/users/${toIDUser}/tokens`).once('value').then(function(snapshot) {
// Handle Promise
const tokenOfGroup = snapshot.val()
// get tokens from the database at particular location get values
const valuess = Object.keys(tokenOfGroup).map(k => tokenOfGroup[k]);
//console.log(' ____________ddd((999999ddd_________________ ' + valuess );
const payload = {
notification: {
title: original.senderName + " :- ",
body: original.content
}
};
return admin.messaging().sendToDevice(valuess, payload);
}, function(error) {
console.error(error);
});
return ;
} else {
// get token from the database at particular location
const tokenss = admin.database().ref(`/users/${toIDUser}/credentials`).once('value').then(function(snapshot) {
// Handle Promise
// The Promise was "fulfilled" (it succeeded).
const credentials = snapshot.val()
// console.log('snapshot ......snapshot.val().name****^^^^^^^^^^^^kensPromise****** :- ', credentials.name);
//console.log('snapshot.....****snapshot.val().token****^^^^^^^^^^^^kensPromise****** :- ', credentials.token);
const deviceToken = credentials.token;
const payload = {
notification: {
title: original.senderName + " :- ",
body: original.content
}
};
return admin.messaging().sendToDevice(deviceToken, payload);
}, function(error) {
console.error(error);
});
}
return ;
});
Google Cloud Functions make it now possible send push notifications from device-to-device without an app server.
From the relevant page on Google Cloud Functions:
Developers can use Cloud Functions to keep users engaged and up to
date with relevant information about an app. Consider, for example, an
app that allows users to follow one another's activities in the app.
In such an app, a function triggered by Realtime Database writes to
store new followers could create Firebase Cloud Messaging (FCM)
notifications to let the appropriate users know that they have gained
new followers.
Example:
The function triggers on writes to the Realtime Database path where followers are stored.
The function composes a message to send via FCM.
FCM sends the notification message to the user's device.
Here is a demo project for sending device-to-device push notifications with Firebase and Google Cloud Functions.
You can use firebase realtime database to do so. You can create data structure for storing chats and add observers for the conversation threads for both users. It still does device - server - device architecture, but in this case there is no additional server on the developers' part. This uses the firebase servers. You can check out a tutorial here (ignore the UI part, although, that is also a good starting point for chat UI frameworks).
Firebase Realtime Chat
If you have fcm(gcm) token of the device to whom you want to send notification. It's just a post request to send the notification.
https://github.com/prashanthd/google-services/blob/master/android/gcm/gcmsender/src/main/java/gcm/play/android/samples/com/gcmsender/GcmSender.java
In my case I use retrofit with this class Message:
public class Message {
private String to;
private String collapseKey;
private Notification notification;
private Data data;
public Message(String to, String collapseKey, Notification notification, Data data) {
this.to = to;
this.collapseKey = collapseKey;
this.notification = notification;
this.data = data;
}
}
Data
public class Data {
private String body;
private String title;
private String key1;
private String key2;
public Data(String body, String title, String key1, String key2) {
this.body = body;
this.title = title;
this.key1 = key1;
this.key2 = key2;
}
}
Notification
public class Notification {
private String body;
private String title;
public Notification(String body, String title) {
this.body = body;
this.title = title;
}
}
this the call
private void sentToNotification() {
String to = "YOUR_TOKEN";
String collapseKey = "";
Notification notification = new Notification("Hello bro", "title23");
Data data = new Data("Hello2", "title2", "key1", "key2");
Message notificationTask = new Message(to, collapseKey, notification, data);
Retrofit retrofit = new Retrofit.Builder()
.baseUrl("https://fcm.googleapis.com/")//url of FCM message server
.addConverterFactory(GsonConverterFactory.create())//use for convert JSON file into object
.build();
ServiceAPI api = new retrofit.create(ServiceAPI.class);
Call<Message> call = api .sendMessage("key=YOUR_KEY", notificationTask);
call.enqueue(new Callback<Message>() {
#Override
public void onResponse(Call<Message> call, retrofit2.Response<Message> response) {
Log.d("TAG", response.body().toString());
}
#Override
public void onFailure(Call<Message> call, Throwable t) {
Log.e("TAG", t.getMessage());
}
});
}
our ServiceAPi
public interface ServiceAPI {
#POST("/fcm/send")
Call<Message> sendMessage(#Header("Authorization") String token, #Body Message message);
}
You can use Retrofit. Subscribe devices to topic news. Send notification from one device to other.
public void onClick(View view) {
HttpLoggingInterceptor logging = new HttpLoggingInterceptor();
logging.setLevel(HttpLoggingInterceptor.Level.BODY);
OkHttpClient.Builder httpClient = new OkHttpClient.Builder();
httpClient.addInterceptor(new Interceptor() {
#Override
public okhttp3.Response intercept(Chain chain) throws IOException {
Request original = chain.request();
// Request customization: add request headers
Request.Builder requestBuilder = original.newBuilder()
.header("Authorization", "key=legacy server key from FB console"); // <-- this is the important line
Request request = requestBuilder.build();
return chain.proceed(request);
}
});
httpClient.addInterceptor(logging);
OkHttpClient client = httpClient.build();
Retrofit retrofit = new Retrofit.Builder()
.baseUrl("https://fcm.googleapis.com")//url of FCM message server
.client(client)
.addConverterFactory(GsonConverterFactory.create())//use for convert JSON file into object
.build();
// prepare call in Retrofit 2.0
FirebaseAPI firebaseAPI = retrofit.create(FirebaseAPI.class);
//for messaging server
NotifyData notifydata = new NotifyData("Notification title","Notification body");
Call<Message> call2 = firebaseAPI.sendMessage(new Message("topic or deviceID", notifydata));
call2.enqueue(new Callback<Message>() {
#Override
public void onResponse(Call<Message> call, Response<Message> response) {
Log.d("Response ", "onResponse");
t1.setText("Notification sent");
}
#Override
public void onFailure(Call<Message> call, Throwable t) {
Log.d("Response ", "onFailure");
t1.setText("Notification failure");
}
});
}
POJOs
public class Message {
String to;
NotifyData notification;
public Message(String to, NotifyData notification) {
this.to = to;
this.notification = notification;
}
}
and
public class NotifyData {
String title;
String body;
public NotifyData(String title, String body ) {
this.title = title;
this.body = body;
}
}
and FirebaseAPI
public interface FirebaseAPI {
#POST("/fcm/send")
Call<Message> sendMessage(#Body Message message);
}
Here is walk around how to get notifications without second server apart from the Firebase one. So we use Firebase only, without additional server.
At the mobile app code, we create its own notifications function by Android libraries like here, not using Firebase libraries like here, without Firebase Cloud messaging.
Here is an example with Kotlin:
private fun notification() {
createNotificationChannel()
val intent = Intent(this, LoginActivity::class.java).apply {
flags = Intent.FLAG_ACTIVITY_NEW_TASK or Intent.FLAG_ACTIVITY_CLEAR_TASK
}
val pendingIntent: PendingIntent = PendingIntent.getActivity(this, 0, intent, 0)
val notificationBuilder = NotificationCompat.Builder(this, "yuh_channel_id")
.setSmallIcon(R.drawable.ic_send)
.setContentText("yuh")
.setContentText("yuh")
.setAutoCancel(true)
.setPriority(NotificationCompat.PRIORITY_DEFAULT)
.setContentIntent(pendingIntent)
val notificationManager =
getSystemService(Context.NOTIFICATION_SERVICE) as NotificationManager
notificationManager.notify(0, notificationBuilder.build())
with(NotificationManagerCompat.from(this)) {
// notificationId is a unique int for each notification that you must define
notify(0, notificationBuilder.build())
}
}
private fun createNotificationChannel() {
// Create the NotificationChannel, but only on API 26+ because
// the NotificationChannel class is new and not in the support library
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
val name = "yuh_channel"
val descriptionText = "yuh_description"
val importance = NotificationManager.IMPORTANCE_DEFAULT
val CHANNEL_ID = "yuh_channel_id"
val channel = NotificationChannel(CHANNEL_ID, name, importance).apply {
description = descriptionText
}
// Register the channel with the system
val notificationManager: NotificationManager =
getSystemService(Context.NOTIFICATION_SERVICE) as NotificationManager
notificationManager.createNotificationChannel(channel)
}
In the Firebase database, create collection "pending notifications". Documents should contain user name (to send notification to) and source name (where should user go upon tapping the notification).
In the app code, implement option for adding new records to the Pending Notifications collection. E. g. if user A sends message to user B, then the document with the id of user B (who will be notified) is created in the collection.
In the app code, set up background (when the app is not visible to the user) service. Like here. In the background service, set up a listener for changes in the "Notifications Pending" collection. When the new record with the user id comes to the collection, call the notification function created in the paragrath 1 supra and delete the consequent record from the collection.
So I had an idea here. See: If the FCM, as well as the GCM, has a endpoit to http request where we can send a post json with our message data, including the token (s) of devices that we want this message to be delivered.
So why not send a post to Firebase server with this notification to be delivered to user B? you understand ?
So, you send the message and chat with a call post to ensure delivery of the notification if the user is with your app in the background. I am also in need of it soon, I will test later. What do you say about?
Simplest way :
void sendFCMPush(String msg,String token) {
HttpLoggingInterceptor logging = new HttpLoggingInterceptor();
logging.setLevel(HttpLoggingInterceptor.Level.BODY);
OkHttpClient.Builder httpClient = new OkHttpClient.Builder();
httpClient.addInterceptor(new Interceptor() {
#Override
public okhttp3.Response intercept(Chain chain) throws IOException {
Request original = chain.request();
// Request customization: add request headers
Request.Builder requestBuilder = original.newBuilder()
.header("Authorization", "key="+Const.FIREBASE_LEGACY_SERVER_KEY); // <-- this is the important line
Request request = requestBuilder.build();
return chain.proceed(request);
}
});
httpClient.addInterceptor(logging);
OkHttpClient client = httpClient.build();
Retrofit retrofit = new Retrofit.Builder()
.baseUrl("https://fcm.googleapis.com/")//url of FCM message server
.client(client)
.addConverterFactory(GsonConverterFactory.create())//use for convert JSON file into object
.build();
// prepare call in Retrofit 2.0
FirebaseAPI firebaseAPI = retrofit.create(FirebaseAPI.class);
//for messaging server
NotifyData notifydata = new NotifyData("Chatting", msg);
Call<Message> call2 = firebaseAPI.sendMessage(new Message(token, notifydata));
call2.enqueue(new Callback<Message>() {
#Override
public void onResponse(Call<Message> call, retrofit2.Response<Message> response) {
Log.e("## SUCCES #E$#", response.body().toString());
}
#Override
public void onFailure(Call<Message> call, Throwable t) {
Log.e("E$ FAILURE E$#", t.getMessage());
}
});
}
Create Class to make Object:
public class Message {
String to;
NotifyData data;
public Message(String to, NotifyData data) {
this.to = to;
this.data = data;
}
}
Create Class to make Object:
public class Notification {
String title;
String message;
enter code here`enter code here`
public Notification(String title, String message) {
this.title = title;
this.message = message;
}
}
I need to make a POST request and send some data. I'm using the service worker sync to handle offline situation.
But is there a way to pass the POST data to the service worker, so it makes the same request again?
Cause apparently the current solution is to store requests in some client side storage and after client gets connection - get the requests info from the storage and then send them.
Any more elegant way?
PS: I thought about just making the service worker send message to the application code so it does the request again ... but unfortunately it doesn't know the exact client that registered the service worker :(
You can use fetch-sync
or i use postmessage to fix this problem, which i agree that indexedDB looks trouble.
first of all, i send the message from html.
// send message to serviceWorker
function sync (url, options) {
navigator.serviceWorker.controller.postMessage({type: 'sync', url, options})
}
i got this message in serviceworker, and then i store it.
const syncStore = {}
self.addEventListener('message', event => {
if(event.data.type === 'sync') {
// get a unique id to save the data
const id = uuid()
syncStore[id] = event.data
// register a sync and pass the id as tag for it to get the data
self.registration.sync.register(id)
}
console.log(event.data)
})
in the sync event, i got the data and fetch
self.addEventListener('sync', event => {
// get the data by tag
const {url, options} = syncStore[event.tag]
event.waitUntil(fetch(url, options))
})
it works well in my test, what's more you can delete the memory store after the fetch
what's more, you may want to send back the result to the page. i will do this in the same way by postmessage.
as now i have to communicate between each other, i will change the fucnction sync into this way
// use messagechannel to communicate
sendMessageToSw (msg) {
return new Promise((resolve, reject) => {
// Create a Message Channel
const msg_chan = new MessageChannel()
// Handler for recieving message reply from service worker
msg_chan.port1.onmessage = event => {
if(event.data.error) {
reject(event.data.error)
} else {
resolve(event.data)
}
}
navigator.serviceWorker.controller.postMessage(msg, [msg_chan.port2])
})
}
// send message to serviceWorker
// you can see that i add a parse argument
// this is use to tell the serviceworker how to parse our data
function sync (url, options, parse) {
return sendMessageToSw({type: 'sync', url, options, parse})
}
i also have to change the message event, so that i can pass the port to sync event
self.addEventListener('message', event => {
if(isObject(event.data)) {
if(event.data.type === 'sync') {
// in this way, you can decide your tag
const id = event.data.id || uuid()
// pass the port into the memory stor
syncStore[id] = Object.assign({port: event.ports[0]}, event.data)
self.registration.sync.register(id)
}
}
})
up to now, we can handle the sync event
self.addEventListener('sync', event => {
const {url, options, port, parse} = syncStore[event.tag] || {}
// delete the memory
delete syncStore[event.tag]
event.waitUntil(fetch(url, options)
.then(response => {
// clone response because it will fail to parse if it parse again
const copy = response.clone()
if(response.ok) {
// parse it as you like
copy[parse]()
.then(data => {
// when success postmessage back
port.postMessage(data)
})
} else {
port.postMessage({error: response.status})
}
})
.catch(error => {
port.postMessage({error: error.message})
})
)
})
At the end. you cannot use postmessage to send response directly.Because it's illegal.So you need to parse it, such as text, json, blob, etc. i think that's enough.
As you have mention that, you may want to open the window.
i advice that you can use serviceworker to send a notification.
self.addEventListener('push', function (event) {
const title = 'i am a fucking test'
const options = {
body: 'Yay it works.',
}
event.waitUntil(self.registration.showNotification(title, options))
})
self.addEventListener('notificationclick', function (event) {
event.notification.close()
event.waitUntil(
clients.openWindow('https://yoursite.com')
)
})
when the client click we can open the window.
To comunicate with the serviceworker I use a trick:
in the fetch eventlistener I put this:
self.addEventListener('fetch', event => {
if (event.request.url.includes("sw_messages.js")) {
var zib = "some data";
event.respondWith(new Response("window.msg=" + JSON.stringify(zib) + ";", {
headers: {
'Content-Type': 'application/javascript'
}
}));
}
return;
});
then, in the main html I just add:
<script src="sw_messages.js"></script>
as the page loads, global variable msg will contain (in this example) "some data".
I use my postgres database query to determine my next action. And I need to wait for the results before I can execute the next line of code. Now my conn.query returns a Future but I can't manage to get it async when I place my code in another function.
main() {
// get the database connection string from the settings.ini in the project root folder
db = getdb();
geturl().then((String url) => print(url));
}
Future geturl() {
connect(db).then((conn) {
conn.query("select trim(url) from crawler.crawls where content IS NULL").toList()
.then((result) { return result[0].toString(); })
.catchError((err) => print('Query error: $err'))
.whenComplete(() {
conn.close();
});
});
}
I just want geturl() to wait for the returned value but whatever I do; it fires immediately. Can anyone point me a of a piece of the docs that explains what I am missing here?
You're not actually returning a Future in geturl currently. You have to actually return the Futures that you use:
Future geturl() {
return connect(db).then((conn) {
return conn.query("select trim(url) from crawler.crawls where content IS NULL").toList()
.then((result) { return result[0].toString(); })
.catchError((err) => print('Query error: $err'))
.whenComplete(() {
conn.close();
});
});
}
To elaborate on John's comment, here's how you'd implement this using async/await. (The async/await feature was added in Dart 1.9)
main() async {
try {
var url = await getUrl();
print(url);
} on Exception catch (ex) {
print('Query error: $ex');
}
}
Future getUrl() async {
// get the database connection string from the settings.ini in the project root folder
db = getdb();
var conn = await connect(db);
try {
var sql = "select trim(url) from crawler.crawls where content IS NULL";
var result = await conn.query(sql).toList();
return result[0].toString();
} finally {
conn.close();
}
}
I prefer, in scenarios with multiple-chained futures (hopefully soon a thing of the past once await comes out), to use a Completer. It works like this:
Future geturl() {
final c = new Completer(); // declare a completer.
connect(db).then((conn) {
conn.query("select trim(url) from crawler.crawls where content IS NULL").toList()
.then((result) {
c.complete(result[0].toString()); // use the completer to return the result instead
})
.catchError((err) => print('Query error: $err'))
.whenComplete(() {
conn.close();
});
});
return c.future; // return the future to the completer instead
}
To answer your 'where are the docs' question: https://www.dartlang.org/docs/tutorials/futures/
You said that you were trying to get your geturl() function to 'wait for the returned value'. A function that returns a Future (as in the example in the previous answer) will execute and return immediately, it will not wait. In fact that is precisely what Futures are for, to avoid code doing nothing or 'blocking' while waiting for data to arrive or an external process to finish.
The key thing to understand is that when the interpreter gets to a call to then() or 'catchError()' on a Future, it does not execute the code inside, it puts it aside to be executed later when the future 'completes', and then just keeps right on executing any following code.
In other words, when using Futures in Dart you are setting up chunks of code that will be executed non-linearly.
I want to store position coords (latitude, longitude) in a table in my MySQL DB querying a url in a way similar to this one: http://locationstore.com/postlocation.php?latitude=var1&longitude=var2 every ten seconds. PHP script works like a charm. Getting the coords in the device ain't no problem either. But making the request to the server is being a hard one. My code goes like this:
public class LocationHTTPSender extends Thread {
for (;;) {
try {
//fetch latest coordinates
coords = this.coords();
//reset url
this.url="http://locationstore.com/postlocation.php";
// create uri
uri = URI.create(this.url);
FireAndForgetDestination ffd = null;
ffd = (FireAndForgetDestination) DestinationFactory.getSenderDestination
("MyContext", uri);
if(ffd == null)
{
ffd = DestinationFactory.createFireAndForgetDestination
(new Context("MyContext"), uri);
}
ByteMessage myMsg = ffd.createByteMessage();
myMsg.setStringPayload("doesnt matter");
((HttpMessage) myMsg).setMethod(HttpMessage.POST);
((HttpMessage) myMsg).setQueryParam("latitude", coords[0]);
((HttpMessage) myMsg).setQueryParam("longitude", coords[1]);
((HttpMessage) myMsg).setQueryParam("user", "1");
int i = ffd.sendNoResponse(myMsg);
ffd.destroy();
System.out.println("Lets sleep for a while..");
Thread.sleep(10000);
System.out.println("woke up");
} catch (Exception e) {
// TODO Auto-generated catch block
System.out.println("Exception message: " + e.toString());
e.printStackTrace();
}
}
I haven't run this code to test it, but I would be suspicious of this call:
ffd.destroy();
According to the API docs:
Closes the destination. This method cancels all outstanding messages,
discards all responses to those messages (if any), suspends delivery
of all incoming messages, and blocks any future receipt of messages
for this Destination. This method also destroys any persistable
outbound and inbound queues. If Destination uses the Push API, this
method will unregister associated push subscriptions. This method
should be called only during the removal of an application.
So, if you're seeing the first request succeed (at least sometimes), and subsequent requests fail, I would try removing that call to destroy().
See the BlackBerry docs example for this here
Ok so I finally got it running cheerfully. The problem was with the transport selection; even though this example delivered WAP2 (among others) as an available transport in my device, running the network diagnostics tool showed only BIS as available. It also gave me the connection parameters that I needed to append at the end of the URL (;deviceside=false;ConnectionUID=GPMDSEU01;ConnectionType=mds-public). The code ended up like this:
for (;;) {
try {
coords.refreshCoordinates();
this.defaultUrl();
this.setUrl(stringFuncs.replaceAll(this.getUrl(), "%latitude%", coords.getLatitude() + ""));
this.setUrl(stringFuncs.replaceAll(this.getUrl(), "%longitude%", coords.getLongitude() + ""));
cd = cf.getConnection(this.getUrl());
if (cd != null) {
try {
HttpConnection hc = (HttpConnection)cd.getConnection();
final int i = hc.getResponseCode();
hc.close();
} catch (Exception e) {
}
}
//dormir
Thread.sleep(15000);
} catch (Exception e) {
} finally {
//cerrar conexiones
//poner objetos a null
}
Thanks for your help #Nate, it's been very much appreciated.