I'm using flutter to work on an bluetooth low energy app, via the flutterBlue library, in which we are potentially connecting to multiple peripherals at the same time.
I am able to connect to multiple peripherals if I connect to them individually and send commands to all of them simultaneously.
For state management, my BluetoothHelper is the Model for my ScopedModel.
class BluetoothHelper extends Model {
bool isProcessing = false;
int val = 0;
FlutterBlue flutterBlue = FlutterBlue.instance; //bluetooth library instance
StreamSubscription scanSubscription;
Map<DeviceIdentifier, ScanResult> scanResults = new Map();
/// State
StreamSubscription stateSubscription;
BluetoothState state = BluetoothState.unknown;
/// Device
List<BluetoothDevice> devicesList = new List(); //todo
bool get isConnected => (deviceList.size != 0);
StreamSubscription deviceConnection;
StreamSubscription deviceStateSubscription;
List<BluetoothService> services = new List();
Map<Guid, StreamSubscription> valueChangedSubscriptions = {};
BluetoothDeviceState deviceState = BluetoothDeviceState.disconnected;
Future startScan(String uuid) async {
isProcessing = true;
if (val == 0) {
Future.delayed(Duration(milliseconds: 25), () => scanAndConnect(uuid));
val++;
} else {
Future.delayed(Duration(seconds: 4), () => scanAndConnect(uuid));
}
}
scanAndConnect(String uuid){
scanSubscription =
flutterBlue.scan(timeout: const Duration(seconds: 120), withServices: [
//new Guid('FB755D40-8DE5-481E-A369-21C0B3F39664')]
]).listen((scanResult) {
if (scanResult.device.id.toString() == uuid) {
scanResults[scanResult.device.id] = scanResult;
print("found! Attempting to connect" + scanResult.device.id.toString());
device = scanResult.device;
//connect(device);
connect(device);
}
}, onDone: stopScan);
}
Future connect(BluetoothDevice d) {
deviceConnection = flutterBlue.connect(d).listen(
null,
);
deviceStateSubscription = d.onStateChanged().listen((s) {
if (s == BluetoothDeviceState.connected) {
stopScan();
d.discoverServices().then((s) {
print("connected to ${device.id.toString()}");
services = s;
services.forEach((service) {
var characteristics = service.characteristics;
for (BluetoothCharacteristic c in characteristics) {
if (c.uuid.toString() == '') {//we look for the uuid we want to write to
String handshakeValue ; //value is initiliazed here in code
List<int> bytes = utf8.encode(handshakeValue);
d.writeCharacteristic(c, bytes,
type: CharacteristicWriteType.withResponse);
devicesList.add(d);
}
}
});
});
}
});
}
}
I am trying to loop throw all peripheral Unique Identifier (UID) and then have them connect one after the other programmatically.
This wasnt working out great. It would always end up connecting to the very last peripheral. Seems like the flutterblue instance can only scan for one uid at a time, and if it receives another request, it immediately drops the last request and moves to the new one.
I applied this same logic to the connection of an individual peripheral logic where I'd tap one peripheral and the second immediately and it'd connect to the second one. (I'm not currently blocking the UI or anything while the connection process takes place)
I need to wait till the first peripheral is connected before moving onto the next one.
The code above is the only way I've gotten my peripherals but there are huge problems with this code. It can currently only connect to 2 devices. It's using delays instead of callbacks to achieve connection by giving enough time for the scan and connect to happen before moving onto the second peripheral.
My first instinct was to make the convert the startScan and connect methods into async methods but this isnt working out well as I'd hope.
{await connect(device); } => gives "The built in Identifier "await" cant be used as a type. I could just be setting up the asyncs incorrectly.
I have looked around for alternatives and I've come upon Completers and Isolates. I'm not sure how relevant that might be.
UI SIDE :
I have the following method set for the ontap of a button wrapped within a scoped model descendant. This is going to reliably load peripheralUIDs list with a few uids and then connect to them one after the other.
connectAllPeripherals(BluetoothHelper model, List<String> peripheralUIDs) {
for(var uuid in peripheralUIDs) { //list of strings containing the uuids for the peripherals I want to connect to
model.startScan(uuid);
}
}
Don't know if this point is still an issue.
Assuming your issue hasn't since been fixed. I think the issue you have is trying to maintain the connections within Flutter (rather than just connecting multiple devices and letting Flutter_Blue/the hardware manage the connections).
I've got it happily connecting to multiple devices; after you've setup the instance maintaining a list of multiple device attributes.
i.e. I made a ble-device class which contained each of the following:
StreamSubscription deviceConnection;
StreamSubscription deviceStateSubscription;
List<BluetoothService> services = new List();
Map<Guid, StreamSubscription> valueChangedSubscriptions = {};
BluetoothDeviceState deviceState = BluetoothDeviceState.disconnected;
Maintaining a LinkedHashMap with a new object initialised from the class above for each device connected works nicely.
Other than that - Flutter_Blue will only allow 1 concurrent request call at a time (like reading a characteristic), but you can stack them pretty easily with
await
with the above, I'm able to poll multiple devices within a few milliseconds of each other.
Don't know if that helps - but with any luck, someone also coming across my problem will hit this and save some time.
Related
I have been getting this problem now a few times when I'm coding and I think I just don't understand the way SwiftUI execute the order of the code.
I have a method in my context model that gets data from Firebase that I call in .onAppear. But the method doesn't execute the last line in the method after running the whole for loop.
And when I set breakpoints on different places it seems that the code first is just run through without making the for loop and then it returns to the method again and then does one run of the for loop and then it jumps to some other strange place and then back to the method again...
I guess I just don't get it?
Has it something to do with main/background thread? Can you help me?
Here is my code.
Part of my UI-view that calls the method getTeachersAndCoursesInSchool
VStack {
//Title
Text("Settings")
.font(.title)
Spacer()
NavigationView {
VStack {
NavigationLink {
ManageCourses()
.onAppear {
model.getTeachersAndCoursesInSchool()
}
} label: {
ZStack {
// ...
}
}
}
}
}
Here is the for-loop of my method:
//Get a reference to the teacher list of the school
let teachersInSchool = schoolColl.document("TeacherList")
//Get teacherlist document data
teachersInSchool.getDocument { docSnapshot, docError in
if docError == nil && docSnapshot != nil {
//Create temporary modelArr to append teachermodel to
var tempTeacherAndCoursesInSchoolArr = [TeacherModel]()
//Loop through all FB teachers collections in local array and get their teacherData
for name in teachersInSchoolArr {
//Get reference to each teachers data document and get the document data
schoolColl.document("Teachers").collection(name).document("Teacher data").getDocument {
teacherDataSnapshot, teacherDataError in
//check for error in getting snapshot
if teacherDataError == nil {
//Load teacher data from FB
//check for snapshot is not nil
if let teacherDataSnapshot = teacherDataSnapshot {
do {
//Set local variable to teacher data
let teacherData: TeacherModel = try teacherDataSnapshot.data(as: TeacherModel.self)
//Append teacher to total contentmodel array of teacherdata
tempTeacherAndCoursesInSchoolArr.append(teacherData)
} catch {
//Handle error
}
}
} else {
//TODO: Error in loading data, handle error
}
}
}
//Assign all teacher and their courses to contentmodel data
self.teacherAndCoursesInSchool = tempTeacherAndCoursesInSchoolArr
} else {
//TODO: handle error in fetching teacher Data
}
}
The method assigns data correctly to the tempTeacherAndCoursesInSchoolArr but the method doesn't assign the tempTeacherAndCoursesInSchoolArr to self.teacherAndCoursesInSchool in the last line. Why doesn't it do that?
Most of Firebase's API calls are asynchronous: when you ask Firestore to fetch a document for you, it needs to communicate with the backend, and - even on a fast connection - that will take some time.
To deal with this, you can use two approaches: callbacks and async/await. Both work fine, but you might find that async/await is easier to read. If you're interested in the details, check out my blog post Calling asynchronous Firebase APIs from Swift - Callbacks, Combine, and async/await | Peter Friese.
In your code snippet, you use a completion handler for handling the documents that getDocuments returns once the asynchronous call returns:
schoolColl.document("Teachers").collection(name).document("Teacher data").getDocument { teacherDataSnapshot, teacherDataError in
// ...
}
However, the code for assigning tempTeacherAndCoursesInSchoolArr to self.teacherAndCoursesInSchool is outside of the completion handler, so it will be called before the completion handler is even called.
You can fix this in a couple of ways:
Use Swift's async/await for fetching the data, and then use a Task group (see Paul's excellent article about how they work) to fetch all the teachers' data in parallel, and aggregate them once all the data has been received.
You might also want to consider using a collection group query - it seems like your data is structure in a way that should make this possible.
Generally, iterating over the elements of a collection and performing Firestore queries for each of the elements is considered a bad practice as is drags down the performance of your app, since it will perform N+1 network requests when instead it could just send one single network request (using a collection group query).
I'm using ngrx/component-store and loving it so far. Having prior store knowledge building my own simple ones, the only real headache I've had so far is when I've had to update an array and figured out I have to always create a new one for the internal compare() pipe to realize the array got updated.
Anyway, reading through the documentation it talks about updater methods and patchState. To me they do exactly the same thing, but their creation is slightly different. You would call patchState inside of a method while this.updater() returns a method giving you a function you can expose in your service. Anytime I'm updating my state it's always after a network call. I assume there are plenty of scenarios where you'd want to update your state without a network call so this is why you would want to have an updater available to your component to call. The question is if an updater and patchState are really doing the same thing then is it a better practice to call an updater in an effect or use patchState, or maybe am I putting too much logic in my effect?
On a side note, the docs say an updater method is supposed to be a pure function. If you're using it to your push an object onto an array then is it really pure?
// adding the selectors so people know what components are subscribing to
readonly approvals$ = this.select(state => state.requestApprovals);
readonly registration$ = this.select(state => state);
readonly updateAssessment = this.effect(($judgement: Observable<{id: string, isApproved: boolean}>) => {
return $judgement.pipe(
switchMap((evaluation) => {
const state = this.get();
return this.requestApproval.patch(state.id, state.companyName, evaluation.id, evaluation.isApproved).pipe(
tapResponse(
(result) => {
// is it better to call patchState()?
this.patchState((state) => {
for(let i = 0; i < state.requestApprovals.length; i++) {
if(state.requestApprovals[i].id == result.id) {
state.requestApprovals[i].isApproved = result.isApproved;
}
}
// the take away is you must assign a whole new array object when you update it.
state.requestApprovals = Object.assign([], state.requestApprovals);
return state;
});
// or this updater?
// this.applyDecisionPatch(evaluation);
},
// oh look! another updater reassigning my array to the state so
// it propagates to subscribers to reset the UI
() => { this.reverseDecision(); }
)
);
})
);
});
// this is private to make sure this can only be called after a network request
private readonly applyDecisionPatch = this.updater((state, value: {id: string, isApproved: boolean}) => {
for(let i = 0; i < state.requestApprovals.length; i++) {
if(state.requestApprovals[i].id == value.id) {
state.requestApprovals[i].isApproved = value.isApproved;
}
}
state.requestApprovals = Object.assign([], state.requestApprovals);
return state;
});
Note: There's no tag for ngrx-component-store so couldn't tag it.
An updater can be compared to a reducer.
All the options to modify the state should change it in an immutable way.
A library like ngrx-immer can be used to make this easier.
The main difference is that updater receives the current state, and you can change the state based on it. E.g. a conditional update, or can be used with #ngrx/entity
While with setState and patchState, you just set state properties.
setState updates the whole state object, whereas patchState only sets the given properties and doesn't touch the rest of the state object.
These two methods are also easier to use when you just want to set the state, because you don't have to create an updater function.
To answer the side question, push is not immutable. Instead of creating a new instance, it updates the array instance.
I am working on a basic Support Ticket System. I get the Tickets from Firebase (Either as a Stream or Future).
I want to allow some Filtering Options (e.g. sort by Status and Category).
For this, I thought about using A Future Provider to get the List and a StateNotiferProvider to update the List depending on which filter is being used.
This is the code I have so far:
final ticketListStreamProvider =
RP.FutureProvider((_) => FirestoreService.getTicketList());
class TicketListNotifier extends RP.StateNotifier<List<Ticket>> {
TicketListNotifier() : super([]);
void addTicket(Ticket ticket) {
state = List.from(state)..add(ticket);
}
void removeTicket(Ticket ticket) {
state = List.from(state)..remove(ticket);
}
}
final ticketsController =
RP.StateNotifierProvider<TicketListNotifier, List<Ticket>>(
(ref) => TicketListNotifier(),
);
There are multiple issues I have with that. Firstly it doesn't work.
The StateNotifier accepts a List and not a Future<List>. I need to convert it somehow or rewrite the StateNotifier to accept the Future.
I was trying to stay close to one of the official examples.
(https://github.com/rrousselGit/riverpod/tree/master/examples/todos)
Unfortunately, they don't use data from an outside source like firebase to do it.
What's the best approach to get resolve this issue with which combination of providers?
Thanks
You can fetch your ticketlist in your TicketListNotifier and set its state with your ticket list.
class TicketListNotifier extends RP.StateNotifier<List<Ticket>> {
TicketListNotifier() : super([]);
Future<void> fetchTicketList() async {
FirestoreService.getTicketList().when(
//success
// state = fetched_data_from_firestore
// error
// error handle
)
}
}
final ticketsController =
RP.StateNotifierProvider<TicketListNotifier, List<Ticket>>(
(ref) => TicketListNotifier(),
);
Call this method where you want to fetch it /*maybe in your widget's initState method
ref.read(ticketsController.notifier).fetchTicketList();
Now ref.read(ticketsController); will return your ticket list
Since you have the ticket list in your TicketListNotifier's state you can use your add/remove method like this:
ref.read(ticketsController.notifier).addTicket(someTicket);
I'm successfully using Azure Mobile Services and Xamarin Forms to perform CRUD operations on an SQL DB hosted with Azure. The offline sync portion stores the data in an SQLite db on the phone. There's been a few bumps along the way to get it working as smoothly as we have it now, but this remains to be the last hurdle.
Problem
When the device has no connection (tested using Airplane mode on a variety of physical and emulated devices) - the first time it goes to access any of the offline data, it takes a very long time to return anything. This is the case if the data exists in the SQLite DB or not.
There is no exception thrown, or anything that I can see printed to the logs that indicates what the delay might be.
To give an idea, a PullAsync() on 20 rows might take 5 seconds while online, and that data is stored to the SQLite DB. After putting the device into offline mode, that same operation may take up to 60 seconds. These numbers are quite arbitrary, but the delay is noticeably much too long.
To add to this, this long load only occurs the very first time any Offline Sync method is called. After that, every method is near instant, as I would expect it to be - but why not the first time?
Expected Result
I would expect that because the data is stored on the device already, and no internet connection can be detected, it should return the data almost instantly.
Code
Sync Class
The GetPolicies() method is where the delay would occur.
This is a sample of one of the components. Every other component is the same format, but different data.
IMobileServiceSyncTable<policy_procedure> policyTable = SyncController.policyTable;
public async Task<List<policy_procedure>> GetPolicies(string companyId)
{
//SemaphoreSlim
await SyncController.dbOperation.WaitAsync();
try
{
await SyncController.Initialize();
await policyTable.PullAsync("policy_procedure", policyTable.Where(p => p.fk_company_id == companyId).Where(p=> p.signature!=null || p.signature!=""));
return await policyTable.ToListAsync();
}
catch (Exception ex)
{
//For some reason, when this method is called and the device is offline, it will fall into this catch block.
//I assume this is standard for offline sync, as it's trying to do a pull with no connection, causing it to fail.
//Through using breakpoints, the delay occurs even before it reaches this catch statement.
Console.WriteLine(ex);
return await policyTable.ToListAsync();
}
finally
{
SyncController.dbOperation.Release();
}
}
Sync Controller
public static SemaphoreSlim dbOperation = new SemaphoreSlim(1, 1);
public static MobileServiceClient client;
public static MobileServiceSQLiteStore store;
public static async Task Initialize()
{
try
{
//This line is not standard for Offline Sync.
//The plugin returns true or false for the devices current connectivity.
//It's my attempt to see if there is a connection, to eliminate the load time.
//This does immediately take it back to the try statement in GetPolicies
if (!CrossConnectivity.Current.IsConnected)
return;
if (client ? .SyncContext ? .IsInitialized ? ? false)
return;
client = new MobileServiceClient(AppSettings.azureUrl);
var path = "local.db"; //Normally uses company ID,
path = Path.Combine(MobileServiceClient.DefaultDatabasePath, path);
store = new MobileServiceSQLiteStore(path);
/************************/
#
region Table Definitions in local SQLite DB
//Define all the tables in the sqlite db
..
store.DefineTable < policy_procedure > ();
..#endregion
await client.SyncContext.InitializeAsync(store);
/************/
#
region Offline Sync Tables
..
policyTable = client.GetSyncTable < policy_procedure > ();
..#endregion
}
catch (Exception ex)
{
Console.WriteLine(ex)
}
}
What I've Tried
Well, I'm not too sure what's even causing this, so most of my attempts have been around forcing an exception before this wait time occurs, so that it can fall out of the GetPolicies try-catch, as the wait time appears to be on the PullAsync.
My most recent attempt at this is commented in the code above (SyncController), where I use James Montemagno's Connectivity Plugin to detect the phones network connectivity. (I've tested this separately, and this works correctly without delay.)
The short story is that you don't want to call PullAsync in your GetPolicies method if your device is offline. For example, you could do
try
{
await SyncController.Initialize();
if (CrossConnectivity.Current.IsConnected)
{
await policyTable.PullAsync("policy_procedure", policyTable.Where(p => p.fk_company_id == companyId).Where(p=> p.signature!=null || p.signature!=""));
}
return await policyTable.ToListAsync();
}
but you will also want to handle the case where this is the first time the app runs and so you don't have any records yet.
I'm building a control where there is visual feedback as progress is made for the server responding to the input from the client.
The control will be visible on multiple clients at once, and I want the client that made the change on the control to get slightly different feedback to all the others that will see less information about the state changes.
Is there a meteor inbuilt function to uniquely identify each client which I could use for this? If not, how could I go about making a non-repudiated identifier? It would need to identify two different tabs in the same browser as two different clients.
I couldn't find any easy way to do that built into Meteor, but you can try this depending on your exact use-case.
Here is a technique to track unique client connections per browser window or tab. Each connectionId below can be thought of as a chat room. Since the this.connection.id property inside a Meteor method is not unique per open window or tab, this will store the connection id along with a timestamp inside a collection. When the client closes the browser tab or window, you can use the callback inside the server method this.connection.onClose to lookup that particular connection by its id along with the timestamp and flag it as closed or offline.
Fiber = Npm.require('fibers');
Future = Npm.require('fibers/future');
Meteor.methods({
'client.disconnect': function(connectionId){
check(connectionId, String);
let query = {_id: connectionId};
let options = {$set: {isOnline: false}};
return Connections.update(query, options);
},
'client.connect': function(connectionId){
check(connectionId, String);
let lastSessionTime = Number(new Date().getTime());
let lastSessionId = this.connection.id;
let offlineQuery = {
_id: connectionId,
lastSessionTime: lastSessionTime,
lastSessionId: lastSessionId
}
let offlineOptions = {
$set: {isOnline: false}
}
// When the connection closes, turn this connection offline.
this.connection.onClose(function(){
// You could also remove the document.
Connections.update(offlineQuery, offlineOptions);
});
let onlineQuery = {
_id: connectionId
}
let onlineOptions = {
$set: {
lastSessionTime: lastSessionTime,
lastSessionId: lastSessionId,
isOnline: true}
}
var future = new Future();
Connections.upsert(onlineQuery, onlineOptions, function(err, res){
if (err){
future.throw('Connections.online error');
}else{
future.return(res);
}
});
}
});