Hacker Noon

Smart-contracts: Ethereum vs. Obyte

Smart-contracts: Ethereum vs. Obyte

Smart-contracts have become synonymous with Solidity scripts on Ethereum and they can be used to create many things: multi-signature wallets, fungible and non-fungible tokens, payments with the escrow and so on. In most cases, you don’t need to decentr…

Welcome, Libra: The Facebook Cryptocurrency

Welcome, Libra: The Facebook Cryptocurrency

Facebook leads the creation of a new currency called Libra powered by blockchain.

Silicon Valley giant Facebook has finally unveiled its new project! The company started by Mark Zuckerberg is coming together with 27 organizations around the world to start the non-profit Libra Association and create a new currency called Libra.

“Libra’s mission is to create a simple global financial infrastructure that empowers billions of people around the world,” wrote Zuckerberg in a post on Facebook. “It’s powered by blockchain technology and the plan is to launch it in 2020.”

Libra | A New Global Currency

Libra, according to the Libra Association website, wants to “reinvent money, transform the global economy, so people everywhere can live better lives.”

https://medium.com/media/4c0e881c8164ea2e9ce3a310f2c19ba4/href

“Being able to use mobile money can have an important positive impact on people’s lives because you don’t have to always carry cash, which can be insecure, or pay extra fees for transfers,” explained Zuckerberg. “This is especially important for people who don’t have access to traditional banks or financial services. Right now, there are around a billion people who don’t have a bank account but do have a mobile phone.”

Libra’s main founding members are financial giant like Mastercard, Paypal, Visa, and Stripe, and Silicon Valley companies like Uber, Lyft, eBay, as well as venture capital firm Andreessen Horowitz.

According to Techcrunch, each founding member paid a minimum of $10 million to join. In joining, they gain one vote — or 1% of the total vote (whichever is larger) — in the Libra Association council, and be entitled to a share (proportionate to their investment) of the dividends from interest earned on the Libra reserve users pay fiat currency into to receive Libra.

Facebook says it hopes to reach 100 founding members before the official Libra launch and it’s open to anyone that meets the requirements including direct competitors like Google or Twitter, writes Techcrunch, explaining that the Libra Association, based in Geneva, Switzerland, will meet biannually. “The country was chosen for its neutral status and strong support for financial innovation including blockchain technology,” according to Techcrunch.

The idea behind Libra rests on a few elements and characteristics:

  • Mobile: Libra will be accessible to anyone with an entry-level smartphone and data connectivity.
  • Stable: Libra is backed by a reserve made to keep its value stable.
  • Fast: Libra transactions are quick and easy, no matter where you are sending, or spending, your money.
  • For the world: Libra is a global cryptocurrency that will be available around the world.
  • Scalable: Libra will foster an ecosystem of products and services made to help people use Libra in their everyday lives.
  • Secure: Libra is a cryptocurrency, built on a blockchain designed with security in mind.

According to The New York Times Times, Facebook has sky-high hopes that Libra could become the foundation for a new financial system not controlled by today’s power brokers on Wall Street or central banks.

“It feels like it is time for a better system,” David Marcus, head of Facebook’s blockchain technology research, said in an interview. “This is something that could be a profound change for the entire world.”

1/ Hello, ≋

 — @davidmarcus

In a Twitter thread, Marcus explained: “The journey begins today, and we’re grateful to have such an outstanding group of cofounding members of the Libra Association — the independent non-for-profit entity that will govern this new network and currency, which we hope will become a public good for the world.”

In addition to the Libra Association, Facebook has created a subsidiary named Calibra. It will be led by Marcus and will will build services on top of the Libra network and currency, starting with a wallet — one of many that will launch on Libra.

“One of the reasons for creating Calibra was to have a dedicated, regulated entity that will make strong privacy commitments to its customers as we’ve heard loud and clear that you don’t want social and financial data commingled,” wrote Marcus on Twitter.

We understand we will have to earn your trust.

He continued: “While Facebook/Calibra will continue to contribute and work on this project, we will not have any special rights or privilege with the Libra Association and the network by the time it launches. In other words, we will have the same governance rights as any other member.”

Libra has three distinct components, according to Marcus:

  1. a BFT-based (LibraBFT) permissioned (to start) scalable blockchain;
  2. a reserve-backed cryptocurrency designed to be a medium of exchange;
  3. a new programming language (Move).

https://medium.com/media/320e83583f768666cd5e54b95d65a054/href

The Libra White Paper, in addition to explaining structure and goals, highlights the need for the involvement of the crypto and blockchain community.

  • If you are a researcher or protocol developer, an early preview of the Libra testnet is available under the Apache 2.0 Open Source License, with accompanying documentation. This is just the start of the process, and the testnet is still an early prototype under development, but you can read, build, and provide feedback right away. Since the current focus is on stabilizing the prototype, the project may initially be slower to take community contributions. However, we are committed to building a community-oriented development process and opening the platform to developers — starting with pull requests — as soon as possible.
  • If you want to learn about the Libra Association, read more here.
  • If your organization is interested in becoming a Founding Member or applying for social impact grants from the Libra Association, read more here.

Welcome, Libra!

https://medium.com/media/3c851dac986ab6dbb2d1aaa91205a8eb/href


Welcome, Libra: The Facebook Cryptocurrency was originally published in Hacker Noon on Medium, where people are continuing the conversation by highlighting and responding to this story.

Everything you need to know about Blockchain.

Everything you need to know about Blockchain.

Everything You Need to Know About BlockchainA Financial War is coming.The blockchain revolution is coming. And it’s going to fundamentally change how businesses operate.Make no mistake… this revolution is at least as significant as the one brought abou…

A Return to the Original Vision of Bitcoin?

A Return to the Original Vision of Bitcoin?

MimbleWimble and GRIN Coin: A Return to the Original Vision of Bitcoin?MimbleWimble is a scalable, privacy-based blockchain protocol that verifies transactions without needing to store the entire history of the chain.Image by mseeryWhat is MimbleWimble…

What P2P Insurance Means to Me

What P2P Insurance Means to Me

An explanation of TandaPay’s social agenda productYou say you want a revolution, well, you knowWe all want to change the world. How are we supposed to change the world when protests don’t produce the change we want to see? When unarmed members of local…

Android Unidirectional Flow with LiveData

Android Unidirectional Flow with LiveData

Android Unidirectional Data Flow with LiveData

Improving Coinverse’s Performance and Structure

pc — Ned Scher, Waterfall at Yosemite National Park

The Unidirectional Data Flow (UDF) pattern has improved the usability and performance of Coinverse since the first beta launched in February. Coinverse is the first app creating audiocasts covering technology and news in cryptocurrency. Upgrades using UDF include more efficient newsfeed creation, removal of adjacent native ads, and faster audiocast loading.

The UDF pattern organizes the app into three main areas, view state, events, and effects ensuring the app is modularized and reliable. I learned of the UDF pattern from episode 148 of the Fragmented podcast, Evolving Android architectures (Part 1) with Kaushik Gopal at Instacart and Donn Felker. On first listen it was interesting, but a large overhaul. UDF became compelling as I worked on fixing bugs and realized how complex various flows had become.

The examples of UDF I’ve seen thus far have been with Rx. Rx a powerful and customizable tool for creating streams of data that can be observed in real-time. However, LiveData provides the same benefit of observing state changes and on top of that is simple, directly integrates with Android’s architecture components, and handles Android’s lifecycle events by default. If unfamiliar, check out Google’s Jose Alcérreca’s talk on LiveData. To try out UDF I refactored the newsfeed flows in Coinverse as we’ll walkthrough below.

https://medium.com/media/8b9dd6f492bd3f25f79f7bf5cbe0388e/href

UDF Background

UDF pattern, a.k.a. Unidirectional Data or State Flow was originally popularized in web development with Facebook’s React and Readux state management, and Flux UI libraries. Early Android experimentation can be found from Brian Egan and Guillaume Lung at SoundCloud in 2015. Jake Wharton’s talks on Rx educated developers on reactive programming which are fundamental to UDF.

Growing Number of Android Apps Adopting

To name a few…

App companies adopting UDF

Model View View Model — MVVM

Gem Lake, Yosemite Emigrant Wilderness Trail

For the first iteration of Coinverse I used the Model View View Model (MVVM) approach. MVVM separates the UI from the business logic, improving readability and organization. However, as an app grows with MVVM it becomes a lake of data. Information flows in, out, and around at many points via Activities and Fragments with Data Binding, ViewModels, and Repositories. This adds complexity for keeping track of logic, debugging, and testing, which requires mocking many components.

UDF Advantages

pc — Ned Scher, Waterfall at Yosemite National Park

UDF is a waterfall, information flows in one direction through a single source providing many benefits.

  • One point of entry for streams — The UI and business logic interact through single points of entry.
  • Control UI involving async events — Know exactly when and where things begin and finish
  • Debug issues — Easy to follow sequence of events and identify errors
  • Streamlined tests — The majority of logic is contained in the ViewModel requiring less mocking.

LiveData

LiveData provides a straightforward approach to implementing UDF.

  • Lifecycle aware
  • Can emit multiple or single events
  • Concise code
  • Quick to implement

https://medium.com/media/aece5d95a459fab51fe4afcff559f91b/href

View State, Events, and Effects

ViewState

Coinverse’s main newsfeed

View state is responsible for holding the final view’s persisted data. This entails all of the content shown to a user on a screen, including information about the content such as enabled statuses.

Looking at Coinverse’s main newsfeed above, examples of view state include the contents of the toolbar, what timeframe and the feedtype of feed to display, as well as the contentList to populate the feed with.

Events

ContentSelected(…)

View events consist of both user interface and system initiated actions. UI actions include button presses and text input, whereas system actions might be Android lifecycle events and screen rotation.

In the case of The Coinbase Blog’s content selected above a view event is created, ContentSelected. The event will share information with the business layer to initiate the retrieval of the audiocast selected.

Effects

ContentSwiped(…)

View effects are one time UI occurrences that don’t persist. Effects include navigation, dialogs, and toasts. Effects are created by the business layer to initiate changes in the UI.

When the CCN item above is swiped right, the business layer adds a saved label to the content. The business layer sends an effect, ContentSwiped, informing the UI of the change in the content’s label. The UI can then remove the content from the main newsfeed.

App Structure

Let’s understand how the one-way flow of data is structured. The View handles all UI and system level actions stored in a single stream. The stream is sent to the ViewModel that receives the actions and handles them accordingly in the business logic.

The ViewModel is the source of truth for the view state and creates any necessary effects. The ViewModel also handles requests to the data Repository layer, managing the results loading, success (content), and error states returned from the Repository with an Lce object (more on Lce’s below).

Both the state and effects are observed by the View, updating any changes from the ViewModel in real-time.

Implementation

mainfeed loading

We’ll use Coinverse’s main newsfeed loading as our example for how to implement UDF.

Step 1 of 6 — Define Models

https://medium.com/media/e3e457ec723be5f770f4c050214571d0/href

  • View state — Stored as a LiveData object in the ViewModel, storing the contentList of LiveData type
  • View event and effect — Use Kotlin’s Sealed class to pass one time events

The view state uses LiveData because it’s important the data is immutable vs. MutableLiveData. Otherwise, the flow of data would not be unidirectional, and the state could be changed in many places.

View events and effects are not persisted in the ViewModel. A Sealed class, like an Enum, but on a class level, is used to pass information. Sealed classes define a parent and child class with or without data. TheScreenLoad event is a data class with data about what the ViewModel should load. Whereas the UpdateAds effect is a class without data telling the view to update the ads in the newsfeed.

Step 2 of 6 — Pass events to ViewModel

https://medium.com/media/21b7345af796983c640793c3fbfdf7ee/href

In this example, when the system action of onCreate occurs, a ScreenLoad event is added to the stream of view events and sent from the Fragment to the ViewModel to start creating the main feed.

All of the events created in the View / Fragment are added to a LiveData object _viewEvent, a MutableLiveData object which updates the immutable LiveData object. I’m using the pattern of passing all of the events in onResume based on Kaushik’s sample.

The LiveData stores data wrapped in an Event. As explained by Jose in his LiveData post about events, events ensure a single unique object is added to a stream. This avoids the accidental creation of multiple objects for a single action.

Step 3 of 6 — Process events

mainfeed loaded

https://medium.com/media/1e82719128462cbbc400fb2ceab73db4/href

The ViewModel receives incoming events, handling each event in a when statement based on the type of Sealed ViewEvent class. For ScreenLoad, the entireViewState is updated with the required data. To populate the newsfeed a request to the Repository with getMainFeed is made.

Update State Value

In cases where an attribute of the ViewState needs to be updated rather than the entire ViewState, Kotlin’s shallow copy function is useful.

https://medium.com/media/ce1bf00297c228e57a7216047f915529/href

Step 4 of 6 — Manage Network Requests with LCE Pattern

https://medium.com/media/abb3971ab92689aa13784def4501b3e3/href

To manage network requests, Kaushik introduces the Lce Sealed class object with three states, loading, content, and error. The content state represents a successful request.

https://medium.com/media/115cf44f615dca588145ff82c08df8f1/href

A Sealed class is also useful for returning different types of results.

https://medium.com/media/0282a893889f04b825cc9f73d6a231fb/href

getMainFeed’s network request shares send the Lce states to the ViewModel via the LiveData stream. The PagedListResult class can be passed into the Lce for both the content and error states. The ViewModel will then manage each state appropriately.

Step 5 of 6 — Handle LCE States

mainfeed error

The gif shows something has gone awry. We’ll see how the error is handled in the ViewModel.

https://medium.com/media/2e31d1bd3a6304c6a19b4728f9102597/href

UDF has streamlined both methods of requesting new content from the network and retrieving the updated content from the Room database. Prior to using UDF, Coinverse called two repository methods separately to populate the main newsfeed.

When the feed is loading the existing Room database content is returned so that the user is not staring at an empty screen. For the successful Content case, the updated content from Room is returned. For errors requesting new content, the existing Room content is also displayed similar to theLoading case. In the error above, a SnackBar view effect is passed to the Fragment to display the error message.

The ViewModel observes each Lce state with a LiveData SwitchMap. The SwitchMap passes in one LiveData object and returns a new and different LiveData object that is saved to the view state.

Like all LiveData, a SwitchMap must be observed in the view in order for the value to be emitted within the map inside the ViewModel.

Step 6 of 6 — Observe State Change!

https://medium.com/media/503f19392a8e77dba776d7ab367549a1/href

Now the view state may be observed when an update occurs. The view effects are observed in the same way.

Bonus — Removing Adjacent Ads

auto adjacent ads detection

In addition to a streamlined newsfeed above, UDF has improved how Twitter’s native MoPub ads are shown in the newsfeed. MoPub’s MoPubRecyclerAdapter does not have a built-in approach to avoid adjacent ads from showing. Content can be swiped to be saved or dismissed, eventually causing two ads to appear next to each other. Prior to UDF, this was handled with a manual swipe-to-refresh by the user.

With UDF there is a contentLabeled view state. When the status of the view state changes, meaning an item is labeled to be removed from the main feed, a check for adjacent ads is made. If removing the content creates adjacent ads, the ads are automatically refreshed.

Trade-Offs

Using LiveData for the Unidirectional Data Flow has been great, but it’s not perfect.

LiveData is only applicable for logic impacting the UI. For non-UI logic LiveData will not be observed since it requires lifecycle to be passed in. For these instances, Kotlin coroutines or Rx may be used. If no UI is involved then an even better solution might be to offload the logic completely to the backend with Firebase Cloud Functions.

There’s not as much customization with LiveData for things like threading. With this year’s latest Google I/O updates coroutines appear to easily integrate with LiveData offering more customization.

Coinverse Next Steps

  • Unidirectional Data Flow — Expanding to the rest of Coinverse’s app
  • JUnit testing — Now that the majority of the newsfeed logic is modularized in the ViewModel, JUnit testing will be easier with less mocking of components.
  • Kotlin coroutines — Exploring integration with LiveData

Resources

I’d love your feedback on the Coinverse beta!

Follow me to be updated on a Unidirectional Data Flow sample app and more.

A big thanks to Cristián Gomez and Carlos Daniel of the Medellín Android MeetUp for organizing the talk! If you are in Medellín I recommend stopping by their MeetUp.

Medellín Android talk — Unidirectional Data Flow por Adam Hurwitz


Android Unidirectional Flow with LiveData was originally published in Hacker Noon on Medium, where people are continuing the conversation by highlighting and responding to this story.