Advanced Flutter Project - Third BLoC, StreamControllers and Periodic Observables - Part Six

Repository

https://github.com/flutter/flutter

What Will I Learn?

• You will learn how to use StreamControllers
• You will learn about Periodic Observables
• You will learn how to delay polling
• You will learn about polling APIs
• You will learn how to create a computation BLoC
• You will learn how to approximate a Steem account's recharge time
• You will learn how to use Intl to format timestamps

Requirements

System Requirements:

• IDEA intellij, Visual Studio Code with the Dart/Flutter Plugins, Android Studio or Xcode
• The Flutter SDK on the latest Master Build
• An Android or iOS Emulator or device for testing

OS Support for Flutter:

• Windows 7 SP1 or later (64-bit)
• macOS (64-bit)
• Linux (64-bit)

Required Knowledge

• A basic knowledge Programming
• A fair understanding of Mobile development and Imperative or Object Oriented Programming
• Basic knowledge of the BLoC

Resources for Flutter and this Project:

• Flutter Website: https://flutter.io/
• Flutter Official Documentation: https://flutter.io/docs/
• Flutter Installation Information: https://flutter.io/get-started/install/
• Flutter GitHub repository: https://github.com/flutter/flutter
• Flutter Dart 2 Information: https://github.com/flutter/flutter/wiki/Trying-the-preview-of-Dart-2-in-Flutter
• Flutter Technical Overview: https://flutter.io/technical-overview/
• Dart Website: https://www.dartlang.org/
• Flutter Awesome GitHub Repository: https://github.com/Solido/awesome-flutter
• The Flutter Provider Library: https://github.com/rrousselGit/provider

Sources:

Flutter Logo (Google): https://flutter.io/

Difficulty

• Advanced

Description

In this Flutter Tutorial, we finish implementing the original Utopian Rocks application by adding the Bot Vote Count Down Timer and the bot Vote Power widget to the bottom bar. This process involves creating a third BLoC which makes use of StreamControllers and Periodic Observables. We also need to use another API; the steemit API, to obtain the information that we need to derive these values.

Using StreamControllers in BLoCs

Up until now, when we've implemented out BLoCs, we've mainly separated the StreamSinks and the Streams from one another. In this example, we make use of the StreamController Object; an abstraction over top of the normal StreamSink which contains its own stream. There are some obvious pros and cons to decoupling the Sink and Stream from one another but combining them also gives rise to a set of pros and cons.

In this image, we have some diagrams of two different BLoCs and a StreamController. The StreamController contains a Sink and some methods. The StreamController's Stream that can be listened on and it allows us to add Data and Streams via an .add or .addStream method. In BloC-A, we use the StreamController and are able to add data either from inside of the BLoC or from an external source to this StreamController. The StreamController is then able to serve this data out to the user interface like any other Stream. In BloC-B, the external stream comes into a decoupled Sink. It is then pushed through some kind of transformer; which represents the business logic and then served via a decoupled Stream. The Sink in BloC-B is optional but we don't have the ability to close the decoupled Stream since it doesn't include a Close method. A StreamController however, can be closed just like any other StreamSink.

Periodic Observables and API Polling

The Data that we are serving through this third BLoC needs to be almost real-time; however, the API doesn't give us a Websocket. As a result of this, we need to use a concept called Polling. Polling is when a http client calls a get method on an API after a specified period of time. This get method then pulls in a new response which then updates the data based on any changes that have occurred on the API's server. The downside to polling is that the server can not push changes without the client first requesting the data like with a websocket.

The two pieces of data that we are obtaining through polling are the vote power of the Utopian-io account and an approximate countdown to when the bot will vote on the next batch of contributions. In our application, the polling occurs every 120 seconds and this is done to conserve data and memory. If the application polled the data every second, the amount of data used would be problematic for users of this mobile application. We are able to maintain an illusion of a realtime countdown timer despite this by using a Observable.periodic observable. This observable gives us an incrementer at an set interval of time. In our case, this incrementor, changes its value every second. The counter is subtracted from the computed duration of the countdown. When two minutes pass, the counter is reset and the Countdown Timer and Vote Power are recalculated from the API.

The Source Code for this video may be found here: https://github.com/tensor-programming/utopian-rocks-demo/tree/tensor-programming-part-6

Video Tutorial

Curriculum

Related Videos

• Advanced Flutter Project - Setting Up the Basic Structure - Part One
• Advanced Flutter Project - Adding a Second BloC - Part Two
• Advanced Flutter Project - Best Practices - Generic BLoC Providers - Part Three
• Advanced Flutter Project - Adding Fonts and Fuzzy Timestamps - Part Four
• Advanced Flutter Project - Filtering Contributions and Building Aesthetics - Part Five

Projects and Series

Stand Alone Projects:

• Dart Flutter Cross Platform Chat Application Tutorial
• Building a Temperature Conversion Application using Dart's Flutter Framework
• Managing State with Flutter Flux and Building a Crypto Tracker Application with Dart's Flutter Framework

Building a Calculator

• Building a Calculator Layout using Dart's Flutter Framework
• Finishing our Calculator Application with Dart's Flutter Framework

Movie Searcher Application

• Building a Movie Searcher with RxDart and SQLite in Dart's Flutter Framework (Part 1)
• Building a Movie Searcher with RxDart and SQLite in Dart's Flutter Framework (Part 2)
• Building a Movie Searcher with RxDart and SQLite in Dart's Flutter Framework (Part 3, Final)

Minesweeper Game

• Building a Mine Sweeper Game using Dart's Flutter Framework (Part 1)
• Building a Mine Sweeper Game using Dart's Flutter Framework (Part 2)
• Building a Mine Sweeper Game using Dart's Flutter Framework (Part 3)
• Building a Mine Sweeper Game using Dart's Flutter Framework (Part 4, Final)

Weather Application

• Building a Weather Application with Dart's Flutter Framework (Part 1, Handling Complex JSON with Built Code Generation)
• Building a Weather Application with Dart's Flutter Framework (Part 2, Creating a Repository and Model)
• Building a Weather Application with Dart's Flutter Framework (Part 3, RxCommand (RxDart) and Adding an Inherited Widget)
• Building a Weather Application with Dart's Flutter Framework (Part 4, Using RxWidget to Build a Reactive User Interface)
• Localize and Internationalize Applications with Intl and the Flutter SDK in Dart's Flutter Framework

Redux Todo App

• Building a Todo/CRUD Application In Flutter With Redux - Part 3
• Building a Todo/CRUD Application In Flutter With Redux - Part 2
• Building a Todo/CRUD Application In Flutter With Redux - Part 1

Curriculum

• Building a Multi-Page Application with Dart's Flutter Mobile Framework
• Making Http requests and Using Json in Dart's Flutter Framework
• Building Dynamic Lists with Streams in Dart's Flutter Framework
• Using GridView, Tabs, and Steppers in Dart's Flutter Framework
• Using Global Keys to get State and Validate Input in Dart's Flutter Framework
• The Basics of Animation with Dart's Flutter Framework
• Advanced Physics Based Animations in Dart's Flutter Framework
• Building a Drag and Drop Application with Dart's Flutter Framework
• Building a Hero Animation and an Application Drawer in Dart's Flutter Framework
• Using Inherited Widgets and Gesture Detectors in Dart's Flutter Framework
• Using Gradients, Fractional Offsets, Page Views and Other Widgets in Dart's Flutter Framework
• Making use of Shared Preferences, Flex Widgets and Dismissibles with Dart's Flutter framework
• Using the Different Style Widgets and Properties in Dart's Flutter Framework
• Composing Animations and Chaining Animations in Dart's Flutter Framework
• Building a Countdown Timer with a Custom Painter and Animations in Dart's Flutter Framework
• Reading and Writing Data and Files with Path Provider using Dart's Flutter Framework
• Exploring Webviews and the Url Launcher Plugin in Dart's Flutter Framework
• Adding a Real-time Database to a Flutter application with Firebase
• Building a List in Redux with Dart's Flutter Framework
• Managing State with the Scoped Model Pattern in Dart's Flutter Framework
• Authenticating Guest Users for Firebase using Dart's Flutter Framework
• How to Monetize Your Flutter Applications Using Admob
• Using Geolocator to Communicate with the GPS and Build a Map in Dart's Flutter Framework
• Managing the App Life Cycle and the Screen Orientation in Dart's Flutter Framework
• Making use of General Utility Libraries for Dart's Flutter Framework
• Interfacing with Websockets and Streams in Dart's Flutter Framework
• Playing Local, Network and YouTube Videos with the Video Player Plugin in Dart's Flutter Framework
• Building Custom Scroll Physics and Simulations with Dart's Flutter Framework
• Making Dynamic Layouts with Slivers in Dart's Flutter Framework
• Building a Sketch Application by using Custom Painters in Dart's Flutter Framework
• Using Dart Isolates, Dependency Injection and Future Builders in Dart's Flutter Framework
• Looking at the Main Features of the Beta Three Release of Dart's Flutter Framework

Proof of Work Done

https://github.com/tensor-programming