Within our flutter app we are doing some background processing. For that, we need to create new flutter isolate in our native code so we can run code when activity is not open, based on this guide: https://medium.com/#chetan882777/initiating-calls-to-dart-from-the-native-side-in-the-background-with-flutter-plugin-7d46aed32c47
Now, to not duplicate code and to not cause any concurrency issues, we would also like to have access to that background processing isolate from main flutter UI isolate. That way we can begin processing from both native code and from flutter UI code.
However, there does not seem to be a way for native to pass this Isolate / ControlPort to the main UI side so it can communicate with it. Is there a way I can achieve this (communicate to the same Isolate from both native and UI side)?
From what I see, only way to do this would require native to be the broker between the two sides (send the task to native and then native sends it back to the other side), but it seems like a lot of hassle for one flutter talking to another flutter.
Solution to this is the IsolateNameServer.
One side can call IsolateNameServer.registerPortWithName() and other side can then send messages to that port via IsolateNameServer.lookupPortByName()
Related
I had made a whole chat application using signalr as a socket with the online and offline facility. I am facing a few problems,
Signalr connection is always time out after some time, to overcome that I had condition if hubconnection is not connected then create new hubconnection (onResume app), but still it get hubconnection._callback got increased when sending message and not moving to server side socket. Again need to refresh whole app.
Can someone tell me whether this is problem because there are lot of operations going on and so signalr loses its connection as flutter is single thread and it cannot handle much? or should I use Isolate or inherit widget.
Summary problem:
I cannot send message in chat after sometime. It stores all message in hubconnection._callback and not going for server.
Is anything better solution to keep alive in both Android+iOS.
I had used https://pub.dev/packages/signalr_netcore package.
Please do not mention about firebase.
Any other logic suggestion is appreciable.
Thank you.
I've been using a different package, https://pub.dev/packages/signalr_core, which works fine without any particular issues what I have observed at the moment.
I'm only running about 10 listeners simultaneously, not sure if that is more or less than you. In the package I'm running you can establish connection with automatic reconnect. It looks like this:
HubConnectionBuilder().withAutomaticReconnect().withUrl(....)
It seems like your package have the same functionality... Have you tried that?
As I study about flutter, I notices that there is a thing called isolate.
What is it for? And how do we implement that? Can you give me a simple example?
Thank you in advance.
Isolate in flutter, similar with threading.
"Flutter is single-threaded but it is capable of doing multi-threading
stuff using Isolates (many processes). When Dart starts, there will be
one main Isolate(Thread). This is the main executing thread of the
application, also referred to as the UI Thread. In simple Flutter apps
you will only ever use one Isolate, and your app will run smoothly.
Isolates are:
Dart’s version of Threads. Do not share memory between each other.
Uses Ports and Messages to communicate between them. May use another
processor core if available. Runs code in parallel."
Docs & Simple Example
"Concurrent programming using isolates: independent workers that are
similar to threads but don't share memory, communicating only via
messages."
Official Docs
I need to load a small settings file before showing the first screen.
I'm curently using the PathProvider plugin, but all the functions in it are async.
Is there any way to find the application documents directory synchroniously and then use dart:io sync functions on it? Instead of showing a placeholder for infinite decimal of a second.
EDIT: considering the first 2 answers, probably my explaination was really bad. The answers suggested me to still use async code. Problem is, I need the directory before runApp(), and I dont want my void main() to be async, because this ruins any splash animation for sure.
And the PathProvider API is async, as far as I can see, only because it utilizes MethodChannel, which is async, but functions behind it in PathProvider are pretty much synchronious.
What I'm asking is - is there a way, on Android or IOS, to know ApplicationDocumentsDirectory in sync code? Maybe without using platform-specific code at all?
You can use FutureBuilder for the same purpose without having to worry about execution.
It will allow you to do your process in the background and allows you to show a splash screen UI until your specified process is complete and data is ready to use.
Note: Any plugin or code which needs access to the device's native method channel will be async by default, since access of the method channel itself is supposed to be async.
In Flutter, there are three types of platform channels, and I want to know about the difference between them.
These channels are used to communicate between native code (plugins or native code inside of your project) and the Flutter framework.
MethodChannel
A MethodChannel is used for "communicating with platform plugins using asynchronous method calls". This means that you use this channel to invoke methods on the native side and can return back a value and vise versa.
You can e.g. call a method that retrieves the device name this way.
EventChannel
An EventChannel is used to stream data. This results in having a Stream on the Dart side of things and being able to feed that stream from the native side.
This is useful if you want to send data every time a particular event occurs, e.g. when the wifi connection of a device changes.
BasicMessageChannel
This is probably not something you will want to use. BasicMessageChannel is used to encode and decode messages using a specified codec.
An example of this would be working with JSON or binary data. It is just a simpler version because your data has a clear type (codec) and you will not send multiple parameters etc.
Here is a link to a good explanation for you https://medium.com/flutter-io/flutter-platform-channels-ce7f540a104e
Basically there are two main types:
Method Channels: designed for invoking named pieces of code across Dart and Java/Kotlin or Objective-C/Swift. (From flutter to the platform)
Event Channels: specialized platform channel intended for the use case of exposing platform events to Flutter as a Dart stream. (From the platform to flutter)
#creativecreatorormaybenot answer clears the things, let me add more to this.
Method Channel
This is more like RPC call. You invoke a method from your Flutter app to the native code, the native code does something and finally responds with a success or error. This call could be to get the current battery status, network information or temperature data. Once the native side has responded, it can no longer send more information until the next call.
Method Channel provides platform communication using asynchronous method calls.
Note:- If desired, method calls can also be sent in the reverse
direction, with the platform acting as client to methods implemented
in Dart.
Event Channel
This is more like reactive programming where platform communication using asynchronous event streams. These events could be anything that you need streamed to your Flutter application.Streaming data from the native code to Flutter app like continuously updating BLE or WiFi scanning results, accelerometer and gyro, or even periodic status updates from intensive data collection.
Basic Message Channel
It provides basic messaging services similar to BinaryMessages, but with pluggable message codecs in support of sending strings or semi-structured messages. Messages are encoded into binary before being sent, and binary messages received are decoded into Dart values. The MessageCodec used must be compatible with the one used by the platform plugin.
I have been looking at the Rx Framework aslo refered to as LINQ to events. This is definately a great thing but I have been wondering if anyone sees this as having any uses in web applications rather than just normal windows based apps?
You can use Rx in various call back scenarios, not just when you work 'normal windows apps'. Especially, when you work with Async operations - for ex, you might need to make a call to the server or cloud from your silverlight or desktop client and to receive the data back. Or in cases you'll get a call back from the server (in cases like Polling Duplex).
Also, another scenario for web apps - to invalidate your cache when you receive a data changed event from the model. Just some 'imaginary' code here if you've a cache and model designed accordingly...
var cacheListeners=from sender in myModel.GetDataChangedEvents()
select sender;
//Subscribe
cacheListeners.Subscribe(data=>Cache.Invalidate(data.Key));
Have a look at this http://amazedsaint.blogspot.com/2009/11/systemreactive-or-net-reactive.html
It appears that the original spark for the Rx was around web based programming - in particular to simplify the challenges of AJAX style applications.
Here's a web based example
http://blogs.msdn.com/somasegar/archive/2009/11/18/reactive-extensions-for-net-rx.aspx
See the project http://reactivetrader.com/ to see Rx in use in a web application.