#DataFetching

[memeticsolutions01]

Power of useEffect Hook in React: Essential Guide For Today’s Developers

The useEffect hook in React is a vital tool for managing side effects in functional components. Side effects include things like fetching data, updating the DOM, or setting up subscriptions. In traditional React class components, you’d use lifecycle methods like componentDidMount, componentDidUpdate, and componentWillUnmount for this, but with useEffect, it’s all in one place.

Basic Syntax of useEffect:

useEffect takes two arguments: A function: Contains the side effect logic.

An optional dependency array: Without a dependency array, the effect executes on every render, while an empty array limits it to run only on the initial render.

Cleanup with useEffect: You can also return a cleanup function from useEffect to clear things like timers or subscriptions when the component is about to unmount.

Effects with Dependencies: By adding dependencies (state or props) to the array, you can control when the effect is triggered. It will re-run whenever any value in the array changes.

Best Practices for useEffect: 1. Clean up side effects: Always clear up resources like subscriptions or timers to prevent memory leaks. 2. Manage dependencies: Carefully add dependencies to avoid unnecessary re-renders. 3. Use multiple effects: Split different logic into multiple useEffect hooks to keep your code cleaner.

Conclusion:- The useEffect hook simplifies how you handle side effects in React functional components. It’s flexible and makes managing tasks like data fetching or DOM manipulation much easier.

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Are you interested in creating your own mobile apps? Join us for our upcoming workshop on Introduction to Mobile App Development! This workshop will cover the basics of mobile app development using Flutter. We will learn how to create a basic App in Flutter.

Topics:

1) Flutter overview

2) Dart Basics

3) Your First app

This workshop is perfect for beginners interested in learning the basics of mobile app development. Join us to gain the skills and knowledge to start building your own mobile apps.

🕑Tuesday June 11, 2024,

Time 2:00 PM to 3:00 PM, GMT+0500

Venue: Online

Registration:

https://tinyurl.com/NuAppDev01

Online Workshop Link: (You will receive a link via email 3-6 hours before the workshop)

[technorizesoftwaresolutions]

Building Cross-Platform Apps with Swift and Kotlin

In today's tech-driven world, the demand for mobile applications that run seamlessly across different platforms is ever-increasing. Businesses and developers are constantly seeking efficient ways to reach a broader audience without duplicating efforts for multiple operating systems. Enter Swift and Kotlin, two powerful programming languages that, when combined, can streamline the process of building cross-platform apps. In this blog post, we'll explore how Swift and Kotlin can be used together to create high-performance, cross-platform applications.

Why Choose Swift and Kotlin?

Before diving into the technicalities, let's understand why Swift and Kotlin are the go-to choices for cross-platform app development.

Swift: Developed by Apple, Swift is a powerful and intuitive programming language designed for iOS, macOS, watchOS, and tvOS. It offers a robust set of features and is known for its performance and safety.

Kotlin: Created by JetBrains, Kotlin is a modern language that runs on the Java Virtual Machine (JVM) and can be used for Android development. Kotlin is concise, expressive, and interoperable with Java, making it a favorite among Android developers.

Both languages have gained immense popularity in their respective domains, and their capabilities make them ideal for cross-platform development.

Cross-Platform Development Approaches

There are several approaches to cross-platform development, each with its own set of advantages and trade-offs. Here are the main ones:

Native Development: Writing separate codebases for iOS (Swift) and Android (Kotlin). This approach ensures the best performance and user experience but requires maintaining two codebases.

Cross-Platform Frameworks: Using frameworks like Flutter, React Native, or Xamarin to write a single codebase that runs on both iOS and Android. While this saves time and effort, it may not fully leverage the native capabilities of each platform.

Kotlin Multiplatform: This approach allows you to write shared code in Kotlin for logic and business rules, while the platform-specific code is written in Swift for iOS and Kotlin for Android. This balances code reuse with native performance and experience.

Setting Up Your Development Environment

To get started with Swift and Kotlin for cross-platform development, you need to set up your development environment.

Swift Setup:

Install Xcode from the Mac App Store.

Create a new Xcode project and select the appropriate template for your app.

Kotlin Setup:

Install Android Studio from the official website.

Create a new Android project and configure it to use Kotlin.

Kotlin Multiplatform Setup:

Install the Kotlin Multiplatform plugin in Android Studio.

Create a new Kotlin Multiplatform project and configure the shared code module.

Writing Shared Code

With Kotlin Multiplatform, you can write shared code that can be used by both iOS and Android apps. This includes business logic, data models, and networking code.

Creating Shared Modules:

In your Kotlin Multiplatform project, create a shared module where you'll write your shared code.

Use Kotlin to write business logic and other shared functionalities.

Using Shared Code in Swift:

In your Xcode project, add a dependency on the shared module.

Use the shared code written in Kotlin within your Swift codebase.

Example: Networking Code

Let's look at an example of how you can write shared networking code in Kotlin and use it in both Swift and Kotlin.

Shared Networking Code in Kotlin:kotlinCopy codeimport io.ktor.client.HttpClient import io.ktor.client.request.get class ApiService { private val client = HttpClient() suspend fun fetchData(url: String): String { return client.get(url) } }

Using Shared Code in Swift:swiftCopy codeimport shared class DataFetcher { let apiService = ApiService() func fetchData(url: String, completion: @escaping (String) -> Void) { apiService.fetchData(url: url) { data, error in if let data = data { completion(data) } else if let error = error { print("Error fetching data: \(error)") } } } }

Conclusion

Building cross-platform apps with Swift and Kotlin offers a powerful combination of performance, efficiency, and code reuse. By leveraging the strengths of both languages and using Kotlin Multiplatform, developers can create high-quality applications that provide a native experience on both iOS and Android. As the mobile landscape continues to evolve, mastering these tools and techniques will be essential for staying ahead in the world of app development.

Embrace the power of Swift and Kotlin and start building cross-platform apps that deliver the best of both worlds!

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Is Blockchain Gaming Hampered by the Volatility of Crypto? Skip to the content ' ); }, success: function(data) if( jQuery('#search-input').val() =="" ) jQuery('#datafetch').html(""); return; else jQuery('#datafetch').html( data ); }); }

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Data Recovery Calgary

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Are you working around the clock creating new REST endpoints for you clients? Are the requirements constantly changing? Use graphQL with micronaut and give more control to the client.

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Alteryx, the leader in self-service data analytics, has been changing this for a while now. It provides extensive out-of-the-box connectors that are used to retrieve or push data to the cloud.

[ijtsrd]

Covid 19 Datafetcher Using ParseHub Tool with Voice Assistance

by Mariam Fatima | M Ganeshan "Covid-19 Datafetcher Using ParseHub Tool with Voice Assistance"

Published in International Journal of Trend in Scientific Research and Development (ijtsrd), ISSN: 2456-6470, Volume-5 | Issue-1 , December 2020,

URL: https://www.ijtsrd.com/papers/ijtsrd38036.pdf

Paper URL : https://www.ijtsrd.com/computer-science/other/38036/covid19-datafetcher-using-parsehub-tool-with-voice-assistance/mariam-fatima

internationaljournalofmanagement, callforpapermanagement, managementjournal

Main purpose of Web Scraping is to abstract information from single or N websites and then process it into plain structures such as spreadsheets, CSV file or database. Although, in adding to be a very convoluted task, Web Scraping is source and tiresome, primarily when it is carried out manually. Now in this pandemic situation it is very important for all the people have a look at the live cases which are spreading rapidly. Parsehub will help us to fetch the data from the websites more accurately and easily. By using parsehub tool researchers can collect real time data of covid 19 cases which can be easily extracted from anywhere. Parsehub uses machine learning for its relationship engine which is state of the art. 

[tak4hir0]

こんにちは、エムスリー エンジニアリンググループ マルチデバイスチームの藤原です。 昨年末に医師向けのスマホアプリを新たにリリースしました。 スマホアプリ向けの BFF(Backends For Frontends) も新規に開発したのですが、そこには SpringBoot + Kotlin + GraphQL なアプリケーションを採用しています。 GraphQL はチームでの採用は初めてで、私もこのプロジェクトで初めて触りました。 そのような状況だったので GraphQL 周りについては試行錯誤を重ねることとなったのですが、今回はその開発の中で見えてきた プラクティス をいくつか紹介したいと思います。 これから SpringBoot + Kotlin + GraphQL な開発をされる方の参考になれば幸いです。 ボネリークマタカ（某GraphQLの入門書*1の表紙にもこの鳥が描かれている） （Godbolemandar [CC BY-SA 4.0], ウィキメディア・コモンズより） スカラー型の入力チェックは Custom Scalar を使おう 認証結果は GraphQLContext に保存しよう ユーザ情報のフィールドにするべきものとそうじゃないもの 認証が必要であることは Directive で表現しよう ���ラーハンドリング フィールドで Nullable or Non-null を迷うようなら Nullable フィールドの引数で Nullable or Non-null を迷うようなら Non-null 要素追加の可能性がある Enum を使うときは細心の注意を 解決策1. unknown だった場合にどうするか決める 解決策2. フィールドを変える 解決策3. Enum を使わない 先人の知恵を借りる We are hiring ※ この記事に登場する graphql-java 依存のクラス等は以下のライブラリとバージョンを元にしています。 graphql-java 13.0 *2 graphql-java-servlet 8.0.0 *3 graphql-java-tools 5.6.1 *4 graphql-spring-boot-starter 5.10.0 *5 スカラー型の入力チェックは Custom Scalar を使おう GraphQL スキーマのフィールドには引数を渡すことができますが、実行時に入力チェックをしたい場合があります。 GraphQL クエリを発行すると対応するリゾルバーが実行されるので、愚直にやるとリゾルバーで入力チェックのロジックを実装することになります。 以下はメッセージ一覧をページネーションで取得するスキーマとリゾルバーの例です。 type Query { # メッセージ一覧を取得する messages( # 取得件数 first: Int! # 指定した文字列が表すメッセージ以降を取得する after: String ): [Message!] } class QueryResolver : GraphQLQueryResolver { fun messages(first: Int { // first に100以上の数値が指定されたらエラーにしたい if 100) throw IllegalArgumentException() ... } } リゾルバーで取得件数の上限チェックを行なっていますが、他のリゾルバーでも同じような入力チェックを何回も実装しないといけなくなるかもしれず、あまりよくない匂いがします。 GraphQL では独自に任意のスカラー型を定義することができ、スカラー型に入力チェックを実装することでリゾルバーで入力チェックをする必要がなくなります。 スカラー型で入力チェックするようにした場合、スキーマとリゾルバーの実装は以下のようになります。 # ページネーション用の量指定型(1から99の数値) scalar PaginationAmount type Query { # メッセージ一覧を取得する messages( # 取得件数 first: PaginationAmount! # 指定した文字列が表すメッセージ以降を取得する after: String ): [Message!] } typealias PaginationAmount = Int // エイリアスでスキーマ上と型名を合わせると味がいい class QueryResolver : GraphQLQueryResolver { fun { // この処理が実行される時点で first が 100未満であることは保証される ... } } 独自のスカラー型を作成する方法は以下の2ステップです。 Coercing インタフェースを実装したクラスを作成する 作成した Coercing を元に GraphQLScalarType を作成し、Bean に登録する class PaginationAmountCoercing : Coercing<Int, Int { override fun parseLiteral(input: Any): Int? { // 入力チェックを失敗させる場合は CoercingParseLiteralException を throw する ... } ... } @Bean val PaginationAmount = GraphQLScalarType.newScalar() .name("PaginationAmount") .description("A positive integer with an upper bound") .coercing(PaginationAmountCoercing()) .build()!! 認証結果は GraphQLContext に保存しよう SpringBoot をベースにアプリケーションを作っていると認証結果のユーザ情報はリクエストスコープの Bean に保存するような形になりそうですが、 GraphQL には同一リクエストで使いまわすことができるコンテキストの仕組みが用意されています。 AuthContext という独自のクラスに User を持たせる例は以下のようになります。 GraphQLContext インタフェースを実装した AuthContext クラスを作成 build メソッドで AuthContext のインスタンスを返すような GraphQLContextBuilder を作成し Bean に登録 class AuthContext(val user: User?) : GraphQLContext { ... } @Bean fun authContextBuilder(): GraphQLContextBuilder = object : DefaultGraphQLContextBuilder() { override fun build( request: HttpServletRequest, response: HttpServletResponse ): GraphQLContext { // ユーザの情報を取得 val user = ... return AuthContext(user) } } AuthContext の生成はリクエストごとに1回実行されて、結果はリゾルバーで取得することができます。 class QueryResolver : GraphQLQueryResolver { fun messages( first: PaginationAmount, after: String?, environment: DataFetchingEnvironment // 引数に指定することで、ここからコンテキストの取得もできる { val() val user = authContext.user ... } } ユーザ情報のフィールドにするべきものとそうじゃないもの 認証済みユーザ専用の「おすすめコンテンツ」をスキーマで表現しようとすると、ユーザ情報の型におすすめコンテンツのフィールドを追加する形が考えられます。 type Query { # 現在のユーザ（未認証の場合は null） currentUser: User } # ユーザ情報 type User { # 会員の名前 name: String! ... # おすすめコンテンツ一覧 recommendedContents: [RecommendedContent] } ユーザ情報とおすすめコンテンツを取得するクエリは以下のようになります。 query { currentUser { name recommendedContents { ... } } } facebook が提供している GraphQL のサンプル*6と同じ設計方針となっていて一見自然な対応に見えますが、 今後の機能追加の方向によっては問題になってくる可能性があります。 例えば、未認証のユーザに対してもおすすめコンテンツを返さなければならなくなるかもしれません。 おすすめコンテンツ一覧を会員情報のフィールドとしていると、会員ではないユーザについてはそのフィールドにアクセスすることができなくなってしまいます。 このような場合は、会員情報とおすすめコンテンツのリレーションを断つのがシンプルです。 スキーマ定義の一部を修正したものは以下のようになります。 type Query { # 現在のユーザ currentUser: User # おすすめコンテンツ一覧 recommendedContents: [RecommendedContent] } ユーザ情報のフィールドにするものは ユーザを構成している要素である（e.g. メールアドレスなどの登録情報） ユーザの状態を表す要素である（e.g. 保有ポイント数） 他のユーザからも関連が見える必要がある（e.g. SNSの友達一覧） のいずれかの条件を満たすものにするのが良いでしょう。 認証が必要であることは Directive で表現しよう 未認証の場合に結果を返さないフィールド、もしくは型であることを示したいことがあります。 そのような時は Directive という機能を使えば宣言的に情報を付加することができます。 # 認証済みの場合のみアクセス可能 directive @auth on OBJECT | FIELD_DEFINITION type User @auth { name: String! } 実行時の振る舞いを変えるような Directive の実装方法は以下の2ステップです。 SchemaDirectiveWiring インタフェースを実装したクラスを作成する SchemaDirective として Bean に登録する 認証が必要なことを示す Directive の実装は以下のようになります。 class AuthDirective : SchemaDirectiveWiring { override fun): GraphQLFieldDefinition { val originalDataFetcher = environment.fieldDataFetcher val authDataFetcher = DataFetcher<Any { dataFetchingEnvironment val() if (authContext.user != null) { // 認証済みの場合。元のリゾルバーを呼び出す originalDataFetcher.get(dataFetchingEnvironment) } else { // 未認証の場合。 ... } } return environment.setFieldDataFetcher(authDataFetcher) } } @Bean fun = listOf( SchemaDirective("auth", AuthDirective()) ) エラーハンドリング graphql-java でのエラーハンドリングの方法はいくつかありますが、 GraphQLErrorHandler をカスタマイズする方法を紹介します。 デフォルトでは DefaultGraphQLErrorHandler が使われるようになっていて、リゾルバーからスローされた例外は "Internal Server Error(s) while executing query" というメッセージの1つのエラーに集約されてしまい詳細不明となってしまいますが、自由にカスタマイズすることが可能です。 実装方法は GraphQLErrorHandler インタフェースを実装したクラスを作成し、Bean に登録するのみです。 @Component class CustomGraphQLErrorHandler : GraphQLErrorHandler { override fun { // エラーハンドリングを実装する ... } } GraphQLErrorHandler をカスタマイズする以外の方法では、 SpringBoot の @ExceptionHandler アノテーションを使う方法*7 GraphQLError インタフェースを実装した例外をスローする方法 などがありますが、それらと比べると GrphQL の標準的なエラー表現である path や locations の情報がデフォルトで設定されている（他の方法では独自実装が必要） バリデーションエラーについてもカスタマイズ可能 エラーの数もカスタマイズ可能（レスポンスJSONの errors フィールドに任意の要素数で格納できる） などのメリットがあります。どこまでカスタマイズしたいか次第なところもありますが、おそらく一番自由度が高いカスタマイズ方法です。 フィールドで Nullable or Non-null を迷うようなら Nullable Non-null である必要がないフィールドを Non-null で定義してしまうと、取得できたはずのデータを返せなくなる可能性があります。 先ほども例に出したスキーマを例にして説明します。 # Schema type Query { # 現在のユーザ currentUser: User # おすすめコンテンツ一覧 recommendedContents: [RecommendedContent] } # Query query { currentUser { name } recommendedContents { title } } 上記のようなクエリを発行した際に何かしらエラーが発生し、おすすめコンテンツの情報が取得できず以下のような JSON を取得できたとします。 { "data": { "currentUser" : { "name": "エムスリー 太郎" }, "recommendedContents": null }, "errors": [ { "message": "failed to get recommended contents title", "path": ["recommendedContents"] } ] } この時、もし recommendedContents の型が [RecommendedContent]! のように Non-null だった場合、null になるはずだったフィールドの親のオブジェクトが null になります。つまりこの場合は data が null になり、取得できていたはずの currentUser のデータさえもクライアントに返らなくなります。 { "data": null, "errors": [ { "message": "failed to get recommended contents title", "path": ["recommendedContents"] } ] } （data フィールドは最上位のフィールドで Nullable です。） 上記のようなケースが考えられるため、 Nullable か Non-null か迷った時は Nullable とするのが良いと思われます。 また、複数のクエリが同時に問い合わせされた時のことを考えると、Query および Mutation 配下のフィールドは Nullable にしておくのが無難なのかもしれません。 Null可否についての考察はこちらの記事*8がとても参考になりました。 エラーとなった場合を例に出して少し詳しく見てみましたが、互換性の観点でも Nullable の方が望ましいです。 GraphQLをスマホアプリのAPIとして動かしつつスキーマ定義を変更することを考えます。その時、���でにリリースされているバージョンのアプリの互換性を保ちつつ変更する必要が出てきます。 サーバから null が返ってくるとクラッシュする可能性があるので危険！ サーバが null を返さなくなっても問題ないので安全 フィールドの引数で Nullable or Non-null を迷うようなら Non-null 前のセクションではサーバからのレスポンスについては迷うようなら Nullable ということを述べましたが、 クライアントから送られる値については逆のことが言えます。つまり「Nullable or Non-null を迷うようなら Non-null」です。 互換性の観点で再び整理すると以下のようになるためです。 サーバが null を受け取れるようになっても問題ないので安全 サーバが null を受け取れなくなるとクエリ実行できない可能性があるので危険！ 要素追加の可能性がある Enum を使うときは細心の注意を Enum の要素追加はサーバとクライアントで非互換になる可能性があります。 サーバ側は新しい Enum 要素を実装したバージョンをリリースすればいいですが、クライアント側（スマホアプリ）は、新しい Enum 要素を解釈できるバージョンのアプリをリリースし、ユーザの端末に新しいバージョンのアプリをダウンロードしてもらうところまでが必要になります。 Enum をクエリの結果として使う場合、要素追加される前のスキーマ定義を元にコードを生成した旧バージョンのアプリではサーバから返された新しい Enum 要素が解釈できないためです。 アプリの強制アップデート機能によって解消するという手段もありますが、エンジニアの都合でそれをやるのは避けたいです。 4つ目の要素が追加されようとしている Enum を例にして、いくつか解決策��あげます。 enum UserStatus { # 医師 DOCTOR # 医学生 MEDICAL_STUDENT # 薬剤師 PHARMACIST # 薬学生（これから追加される. 古いバージョンのアプリはこの値を知らない） # PHARMACY_STUDENT } 解決策1. unknown だった場合にどうするか決める Appoloクライアントの場合、未定義の Enum が返ってきたときにクラッシュさせないように unknown という状態にできます。 unknown なときにどうするか決めることができれば特に問題にはならないかもしれません。 解決策2. フィールドを変える 要素追加があるごとにフィールドを変えるという対策が取れます。 type User { # 薬学生を含まないステータス status: UserStatus! # 薬学生を含む新しいステータス（しかしフィールド名のネーミングはとても悪い...） newStatus: UserStatus! } フィールド名は拡張可能な形にしておく必要がありますが、命名はとても難しくなることが予想されます。 また、フィールドが増え続けるようなら、それはそれでアンチパターンにハマってしまっていると思われます。。 この方法を取る場合、サポートするクライアントのバージョンがわかっているようならコメント等で残しておくと良いでしょう。 そのバージョンの利用者がいなくなった時にフィールドを削除するのに使えます。 解決策3. Enum を使わない 上記の例であれば Enum にせずに同等の情報を返すフィールドを作る方法も取れます。 type User { # 学生かどうか isStudent: Boolean! # 薬学系ステータスかどうか isPharmacyStatus: Boolean! } 今後拡張の可能性が高いものは Enum として表現するよりも、それ以外のフィールドとして返してクライアント側で決定する方法の方が安全だと思われます。 先人の知恵を借りる 冒頭で述べました通り、GraphQL についてのナレッジがチームにはなかったため悩みどころは多かったです。 特にスキーマ設計についてはサーバサイド、クライアントサイドのエンジニアを交えて議論を重ねました。 スキーマ設計についての指針が欲しいと思っていたところで参考になったドキュメント・書籍を紹介します。 Relay Server Specification*9 Relay Server Specificationは GraphQL の拡張仕様です。スキーマ設計についていくつかの規約を定めています。 Relay に準拠した実装のライブラリも少なくないため、合わせておいて損はないでしょう。 GraphQL 公式サイト*10 GraphQL の一通りの機能についてドキュメントがあり、完全に理解した気分にさせてくれます。機能の説明となっているため使い所などわかりにくいところもありますが、やはり公式ドキュメントは読むべきです。 GraphQL スキーマ設計ガイド*11 あまり日本語化されていない GraphQL の設計周りについて書いてあります。 この書籍が配布された頃にちょうど悩んでいるところだったエラーハンドリングについて特に参考にさせていただきました。 We are hiring 今回は新規アプリのBFFにまつわる話をさせていただきました。 マルチデバイスチームではリリースされたばかりのアプリを成長させるべく一緒に開発に参加してくれる仲間を募集中です。 もちろんサーバサイドに限らず iOS / Android アプリのエンジニアも募集しています。 お気軽にお問い合わせください。 jobs.m3.com *1:初めてのGraphQL, Eve Porcello Alex Banks 著, 尾崎 沙耶 あんどうやすし 訳 *2:https://github.com/graphql-java/graphql-java *3:https://github.com/graphql-java-kickstart/graphql-java-servlet *4:https://github.com/graphql-java-kickstart/graphql-java-tools *5:https://github.com/graphql-java-kickstart/graphql-spring-boot *6:https://github.com/relayjs/relay-examples/tree/master/todo *7:graphql-spring-boot-starterのExceptionハンドリングがめっちゃ便利になってた https://shiraji.hatenablog.com/entry/2019/04/24/080000 *8:When To Use GraphQL Non-Null Fields https://medium.com/@calebmer/when-to-use-graphql-non-null-fields-4059337f6fc8 *9:Relay Server Specification https://relay.dev/docs/en/graphql-server-specification.html *10:https://graphql.org/ *11:GraphQLスキーマ設計ガイド https://github.com/vvakame/graphql-schema-guide

[mobilenamic]

How to avoid C++ models in Qt and why you should care

Many tools rely on web technologies like JavaScript and HTML for mobile app development. But a web view does not offer the performance, features and user experience of native apps.

While the Qt framework is C++ based, you can also code with QML and JavaScript. In fact, you can create full apps without even touching C++.

By reading this guide, you will learn how to avoid C++ models in Qt and develop mobile apps using QML and JavaScript only. These are the main topics covered:

How does the Qt architecture, rendering and compilation work?

How does Qt separate models and views?

Why to use a QML model instead of C++ when working with REST services?

How to add features like offline caching, file downloads or native integrations in QML?

When to use C++ and when QML?

How to structure apps that heavily rely on QML for app logic, models and views?

The Qt Architecture: Why use QML for iOS or Android Apps?

In case you have never heard of Qt: It is a powerful and feature-rich C++ framework used in many different industries. It supports development of apps for Desktop, mobile platforms and embedded systems – all from a single code base.

  One of the best things about Qt is QML, a reactive programming language (sometimes also referred a declarative language) that extends JavaScript. It allows to create stunning apps that save up to 90% of code compared to native development for iOS or Android. With less code and a single code base for iOS, Android and Desktop, your maintenance costs decrease dramatically. You can release updates to different platforms faster and have one team sharing the knowledge.

Custom Rendering and QML Item Trees

In contrast to many other cross-platform solutions, Qt offers an architecture that does not rely on native platform rendering or a web view. It moves all controls and the rendering into the app itself. To show items on the device screen, it only requires a native view with a canvas to draw onto.

This architecture breaks away from the so-called “cookie cutter” apps that have been common in the past. Instead of the native platform renderer, Qt uses app-driven custom rendering. This allows for a unified renderer and app experience across all supported platforms.

But don’t let the fact that Qt relies on C++ mislead you. Since the introduction of QML and JavaScript for rapid UI development, you can create item trees in a customizable and extensible way. You can combine and nest individual QML Items to form a tree that describes your UI. There’s no need to dive into complex C++ code!

This is how the code for a simple QML app with a “Hello World!” page looks like:

import VPlayApps 1.0 import QtQuick 2.0 App { NavigationStack { Page { title: "My First App" AppText { text: "Hello World!" anchors.centerIn: parent } } } }

Native Performance and Compilation of View Code

In the background, each QML Item uses a performant native C++ implementation. When the Qt runtime parses your QML code, it creates all QML Items as C++ objects. With your QML markup and JavaScript logic, you can control and combine them. This makes it easy to build your UI.

There’s no need to create your UI with C++ widgets. Apps created with QML offer the same performance. Qt compiles your QML tree as soon as it parses the code the first time. You get this Just-in-Time (JIT) compilation of QML apps out-of-the-box.

With the Qt Quick Compiler, you can also compile your QML code Ahead-of-Time (AOT). It transforms your QML and JavaScript directly into bytecode. This architecture makes apps powered by QML super fast and performant.

Qt MVC: Models and Views in QML

For most apps, it is a basic task to populate UI views based on some application data. Qt offers a built-in separation into model, view and delegate components. The following example visualizes a set of data records in a list:

import VPlayApps 1.0 import QtQuick 2.0 App { // data model ListModel { id: fruitModel ListElement { name: "Banana" cost: 1.95 } ListElement { name: "Apple" cost: 2.45 } ListElement { name: "Orange" cost: 3.25 } } // list page NavigationStack { Page { title: "List Page" AppListView { anchors.fill: parent model: fruitModel delegate: SimpleRow { text: name detailText: "cost: "+cost } } // AppListView } // Page } // NavigationStack } // App

The AppListView presents you with a scrollable list view. For each ListElement in your ListModel, the view instantiates the delegate Item to visualize each element in your list. In this case, a SimpleRow item represents each list element.

The ListModel type is actually a C++ QAbstractListModel implementation exposed to QML. The above code does not only create a UI tree of C++ objects. It also handles the list data in a C++ data structure – pretty nice!

It is very fast to develop user interfaces this way. And as C++ is actually used under the hood, there is no performance drawback. Still, for long-running, heavy-weight and data-intense calculations it makes sense to move away from QML. In such cases, C++ will outperform JavaScript. For more examples when mixing both languages is worth the extra effort, keep on reading this article. We’ve got you covered with details how to combine C++ code with QML as well!

Why Choose a QML ListModel instead of a Qt C++ Model?

When using QML, many Qt developers tend to believe they should at least code the model in C++. This is not the case. QML is optimized to integrate seamlessly with C++.

All QML code gets compiled to native code with native performance. And when using the Qt Quick Compiler, this already happens during compilation of the app. The QML ListModel offers a simple API and perfectly works together with view types like ListView, GridView or Repeater.

QML Best Practice: Use REST Services and JSON for your ListView

There is another big advantage of using QML and JavaScript as your main coding language: It is super easy to work with REST services and JSON data.

The application logic for QML gets written in JavaScript. QML thus has built-in support to handle variant data types like JSON structures. With a simple HTTP request, you can fetch JSON data and use it in your views.

The following code snippet retrieves and shows a list of todo entries from a REST service:

import VPlayApps 1.0 import QtQuick 2.0 App { // on app start: fetch data from REST api Component.onCompleted: { HttpRequest.get("https://jsonplaceholder.typicode.com/todos") .timeout(5000) .then(function(res) { dataFetched(res.body) }) .catch(function(err) { console.err("Fetch failed:"+err) }); } // dataFetched gets called on success of http request function dataFetched(jsonData) { listView.model = jsonData // set retrieved json data as model for list } // list page NavigationStack { Page { title: "Todo List" AppListView { id: listView anchors.fill: parent delegate: SimpleRow { text: modelData.title } } } } }

Instead of a ListModel, QML also allows you to assign JSON data structures as the model. This is very convenient when working with REST services. You can directly use the retrieved JSON result to display your data.

Drawbacks of Using JSON data for the ListView Model

A JSON structure is no ListModel and thus no QAbstractListModel implementation. You do not have the benefits of a performant C++ model in this case. Also, a JSON array is a variant type. The list can thus not expect a defined data structure to create its elements.

This results in performance and usability drawbacks. For example, when you change or replace the JSON data. The view then parses the whole model again and redraws all items from scratch. This full redraw can take a while and is noticeable by the user. You also lose the current scroll position and advanced features like transition animations are not supported.

At this point, you could think: Let’s create a ListModel and fill it with the JSON data. While this solves the performance problem, another issue quickly pops up: How do you update the model when you fetch new data from the API at a later point?

If you re-create the ListModel from scratch, the view again requires a full redraw. To avoid this, we could compare each entry of the latest JSON data with the current state of the ListModel. This allows to only synchronize changed or new data entries to the model.

But such a manual synchronization requires a lot of extra effort. It also comes with some overhead, especially when you start to compare large data sets. JavaScript and QML are not well suited to perform such data-intense operations.

But don’t worry: The next section introduces a QML component that covers exactly this synchronization. The JsonListModel is a special ListModel implementation that can handle JSON data.

How Does the JsonListModel Work?

The JsonListModel offers an easy way to transform JSON data into a QML ListModel for usage with e.g. an AppListView. This is how you can use the model for our todo list example:

import VPlayApps 1.0 import QtQuick 2.0 App { // on app start: fetch data from REST api Component.onCompleted: { HttpRequest.get("https://jsonplaceholder.typicode.com/todos") .timeout(5000) .then(function(res) { dataFetched(res.body) }) .catch(function(err) { console.err("Fetch failed:"+err) }); } // dataFetched gets called on success of http request function dataFetched(jsonData) { listView.jsonData = jsonData // set retrieved json data as model for list } // list page NavigationStack { Page { title: "Todo List" AppListView { id: listView anchors.fill: parent // property for json data, used as source for JsonListModel property var jsonData: [] // use JsonListModel as model model: JsonListModel { source: listView.jsonData keyField: "id" fields: ["id", "title"] } // delegate delegate: SimpleRow { text: title } } } } }

The JsonListModel holds a local copy of the specified JSON data. Whenever the JSON source changes, the data gets compared to the local copy of the list model. To identify each unique data record, it is important to specify the keyField of your data objects. After diffing the old and new data sets, the JsonListModel applies all detected changes individually. It thus synchronizes the model with the changed JSON data step by step.

The JsonListModel type implements the full QML ListModel API and fires separate events for all changes. The list view can thus only update relevant entries or apply transition animations. This is super useful, as you can e.g. fetch new data and simply replace the old JSON. The JsonListModel will detect all changes, and the ListView updates changed items accordingly – without a full redraw.

Benefits of JsonListModel

You thus get a much better performance and scrolling stays smooth when the list updates:

Json Model: The list jumps to the top after a model update. JsonListModel: The list keeps its scroll position. (the GIF only jumps to the top when it restarts)

To summarize, with the JsonListModel you can:

Fetch JSON data from REST APIs with QML and JavaScript.

Pass your JSON to the model, which synchronizes the data to a ListModel and prepares it for usage in your view.

Show the model data in your QML view, which now only updates items that changed.

You do not require to create a custom model in C++ when working with REST APIs and JSON data. The JsonListModel itself is your C++ model. It is fully usable from QML and can work with JSON objects of any format:

Apart from list views, the JsonListModel also supports the GridView and Repeater types to display model data. It is based on QSyncable, a syncable C++ model implementation by Ben Lau. You can find the full project on GitHub.

The JsonListModel is also available with the free V-Play SDK. The V-Play Apps module used in the above example holds many such useful components. V-Play focuses on making mobile app development with Qt as easy as possible. For example, the HttpRequest type for networking or UI types like NavigationStack are also part of the SDK.

Dynamically Sort or Filter Data with SortFilterProxyModel

To sort and filter list models, C++ Qt offers the QSortFilterProxyModel class. In the same way, you can use the SortFilterProxyModel QML type with any list model in QML. It also works in conjunction with the JsonListModel:

import VPlayApps 1.0 import QtQuick 2.0 App { Page { id: page // property with json data property var jsonData: [ { "id": 1, "title": "Apple", "type": "Fruit" }, { "id": 2, "title": "Ham", "type": "Meat" }, { "id": 3, "title": "Bacon", "type": "Meat" }, { "id": 4, "title": "Banana", "type": "Fruit" } ] // list model for json data JsonListModel { id: jsonModel source: page.jsonData keyField: "id" fields: ["id", "title", "type"] } // SortFilterProxyModel for sorting or filtering lists SortFilterProxyModel { id: sortedModel // use the Component.onCompleted handler to configure SortFilterProxyModel for JsonListModel Component.onCompleted: sourceModel = jsonModel // add a sorter to sort the list by type sorters: StringSorter { id: typeSorter; roleName: "type"; ascendingOrder: true } } // list view AppListView { anchors.fill: parent model: sortedModel delegate: SimpleRow { text: model.title } section.property: "type" section.delegate: SimpleSection { } } // Button change the sorting order AppButton { anchors.horizontalCenter: parent.horizontalCenter anchors.bottom: parent.bottom text: "Change Order" onClicked: typeSorter.ascendingOrder = !typeSorter.ascendingOrder } } // Page }

This example shows a list of different fruit and meat entries. The list entries get sorted by type with the SortFilterProxyModel. You can also change the sorting order by pressing the AppButton.

Similar to JsonListModel, the SortFilterProxyModel is a C++ type exposed to QML. So for this simple QML example, all data and model-related tasks are actually performed by C++ types. When working with REST services and JSON data, you can fully handle all model and view code in QML!

Offline Caching, File Downloads and Native Integrations for your Mobile App

It is very simple to create stunning views and handle application data with QML. But why stop there? Let’s take it even one step further!

Control Your Application from QML

As QML and C++ integrate seamlessly, it is possible to expose any native feature for usage with QML. Available Qt components already allow to work with sensors, SQLite databases and much more. And the V-Play SDK offers lots of additional features. For example to fetch assets at runtime with the DownloadableResource item. It allows you to keep the initial app size small and dynamically load content if required – all with QML.

You can create your own C++ components and register them with QML as well. For iOS and Android apps, you can even add components that

weave-in native iOS code with Obj-C

or run Java Android code over JNI.

Please note that such native code requires custom implementations for each platform then. V-Play already has you covered with the NativeUtils component. It offers lots features like native dialogs, camera and image picker or sharing. The SDK also comes with many V-Play Plugins that integrate 3rd party frameworks for:

server-triggered or local notifications

in-app purchases and monetization

analytics and crash reporting

Firebase authentication and database

and much more.

There is no limit to what you can do – it’s possible to manage your full app logic purely with QML. You can even perform calculations in different threads with a WorkerScript.

App Example with JsonListModel and Offline Caching

Mobile apps have to work properly even without internet access. The Storage component allows to cache data in a simple key-value store. It can save full JSON structures as well. The data gets serialized and converted to string format automatically.

You can thus use the Storage to initialize the JsonListModel with previously cached JSON data. This way, your app can show the latest state of the data even if a fetch request fails:

import VPlayApps 1.0 import VPlay 2.0 import QtQuick 2.0 App { // on app start: fetch data Component.onCompleted: { fetchData() } // list page NavigationStack { Page { title: "Todo List" AppListView { id: listView anchors.fill: parent // property for json data, used as source for JsonListModel property var jsonData: [] // use JsonListModel as model model: JsonListModel { source: listView.jsonData keyField: "id" fields: ["id", "title"] } // delegate delegate: SimpleRow { text: title } } } } // storage for caching Storage { id: cache } // fetch data from cache or from api function fetchData() { // check cached value first var cachedData = cache.getValue("todos") if(cachedData) listView.jsonData = cachedData // load new data from api HttpRequest.get("https://jsonplaceholder.typicode.com/todos") .timeout(5000) .then(function(res) { dataFetched(res.body) }) .catch(function(err) { console.err("Fetch failed:"+err) }); } // dataFetched gets called on success of http request function dataFetched(jsonData) { // cache new data before updating the model cache.setValue("todos", jsonData) listView.jsonData = jsonData // set retrieved json data as model for list } }

In addition to fetched data, you can locally cache new entries as well. As soon as the app has internet connection again, save them to your server and remove the local entries.

We prepared a full demo app for you, which allows to browse and create todo list entries. You can find the full example with caching, local draft entries, list filtering and more on GitHub:

See Full Example on GitHub

When to Use C++ and When to Use QML

Application Development with QML is simple and powerful. But Qt C++ can be more performant, offers many features and is less error-prone. So it’s important to know when to use which.

Coding in QML has several advantages over development with C++:

Coding with QML + JavaScript is very easy to learn and allows to reduce the required amount of code a lot.

Language concepts like states, signals or property bindings are a huge time-saver.

QML makes adding animations simple. You can animate every property of your QML types with simple Animation components.

QML is extensible and flexible. For example, you can extend objects with new properties and features in-line. No need to create a new re-usable type for small extensions.

The QML Rendering Engine offers a great performance. The renderer uses C++ Qt and relies on a hardware accelerated scene graph. This makes it fast enough to power even high-performance games.

Qt app development with C++ has advantages as well. For some scenarios you need features that are only available with Qt C++. Also, C++ is fast and type-safe. This allows to provide the best possible performance for long-running and data-intense calculations.

For these examples, you would choose C++ over QML:

Native C++ code is the right choice for data-intense operations. It will outperform interpreted QML/JavaScript code.

C++ code is type-safe and compiled into object code. For parts where stability and security are important, using C++ helps to make your app less error-prone.

The Qt C++ components offer different and in some cases more features than the QML types. For example, advanced networking features.

It is also possible to mix C++ with native code for Android (over JNI) or iOS (Obj-C or Swift). This allows to provide such native functionality for QML as well.

You might need a 3rd party library that is only available in C++, or have existing code in C++ which you’d like to reuse.

It is possible to code most parts of the application without the need to touch C++. The V-Play SDK and Qt have many QML components available. For a starting point to integrate Qt C++ or make native features available for QML, you can see the guide How to Expose a Qt C++ Class with Signals and Slots to QML.

QML MVC: App Architecture Best Practices and Design Patterns

With all this knowledge and QML benefits in mind, we will use QML for more than only view code. We handle data-related tasks and application logic as well. It thus becomes very important to think about a clean app architecture and component structure for such QML-driven apps. We want to keep our code clean, maintainable and extensible.

Why care about separation of concerns?

The easiness and flexibility of QML can lead to problems. When using signals and property bindings a simple value change can affect many components. Properties that rely on other properties update automatically. They handle the signal and update their value as well. This is even possible across multiple QML Items:

  This doesn’t look complex now. But imagine that we add a few new components with different properties and cross-dependencies:

Different connections between all the items form. You can no longer say for sure what effect a single property change may have for directly or indirectly connected components. In the worst case, this can result in circular dependencies or loops. If you face such issues, this is an indicator for bad component architecture.

This problem gets bigger and bigger the more your project grows. Each component should thus have a clean interface and only manage its own data. This is what separation of concerns means.

Design Patterns like MVC, MVVM or Flux (React Native)

A bad component architecture can quickly lead to unwanted side-effects or corrupted data. Imagine lots of signals firing and event handlers running in unknown order. Your code at different parts of the app changes data seemingly random or with duplicated code. This is a nightmare for debugging, maintenance or refactoring.

For most design patterns, the golden rule is: Keep the code that displays data (view) separate from the code that reads or modifies data (model).

Model-View Separation in QML

Each content view of a V-Play app is usually composed as a Page. The Page type is a view controller, which provides and displays data for the user. By introducing a DataModel component, we can move data handling away from the view:

The DataModel is your central storage for application data. Pages can only access application data with the DataModel. It manages your data in a way that makes sense for your use-case and views. For different views and use-cases, the usage of several DataModel components is possible.

For the app logic, you will also add many functions and signal handlers to your view or model. If not done properly, this results in a lot of fragmented code spread across view items. Once your application gets more complex, it also gets more difficult to maintain your code clean and testable. It gets hard to decide where to perform which action, and duplicate code spread across pages is inevitable.

With the above architecture, the data flow between model and page is bi-directional. This means, pages do not only show model data, but can also write to the model directly. Modern application frameworks like React Native use a different approach. For example, the Flux architecture designed by Facebook favors an unidirectional data flow.

Create a clean Data Flow: QML Architecture inspired by Flux

With Flux, each user interaction propagates the action through a central dispatcher. The dispatcher forwards the action to various stores that hold application data and business logic:

You can read more about a quite sophisticated implementation of such a pattern for QML in this post by Ben Lau: Revised QML Application Architecture Guide with Flux

It’s hard to say if the overhead of a complex solution is worth the effort. For most mobile app projects, a more relaxed implementation with the same advantages is sufficient.

Simple Flux-like Example for Model View Controller Separation in QML

To create a one-directional data flow, we can also take advantage of QML’s built-in signal mechanism. We can ensure a loose coupling between different components. You can find a basic example architecture that applies this pattern in this guide: Separation of Model, View and Logic Code in your Qt App using QML

It introduces a Logic component to dispatch actions from Pages to the DataModel:

Doing a lot of work in QML can quickly result in unreadable and fragmented code. With a clean component architecture and clear responsibilities, you can avoid this. Using an architecture like above helps to provide a consistent app structure that simplifies testing and refactoring.

With the principles shown in this guide, you can create well-structured apps that handle app logic, data-related tasks and view code purely with QML.

  Not sure how to get started? V-Play offers many demos and examples you can use to build a first prototype of your project:

We can also help you out with Qt Trainings and App Development Workshops to get your team started!

  The V-Play SDK is free to use, so make sure to check it out!

Get V-Play Apps

  Do you already have a project or app idea in mind? The V-Play team is here to support you! We can cover the whole process from the first idea up to the release of your app in the stores. Take advantage of our Mobile App Development Services and join the ranks of satisfied V-Play customers:

  If you enjoyed this post, feel free to share it on Facebook or Twitter.

More Relevant App Development Resources

Qt Quick Compiler

How to Expose a Qt C++ Class with Signals and Slots to QML.

Separation of Model, View and Logic Code in your Qt App using QML

Revised QML Application Architecture Guide with Flux

The Best App Development Tutorials & Free App Templates

All of these tutorials come with full source code of the mobile apps! You can copy the code to make your own apps for free!

How to create a mobile app for iOS & Android with a single code base

How to support multiple languages and internationalization in your mobile app

Common Widgets & Controls in a cross-platform App

How to support multiple screen sizes & screen densities – Responsive App Guide

Guide for App Layout

Guide for App Navigation

How to add native code to your mobile App

How to easily style your App with Themes

How to add Animations to your App

How to add a Chat to your Mobile App

How to make a Weather App accessing a REST weather service

Conference App Template

Widget Gallery App Template

Twitter App Template

Messenger App Template

Property Finder App Template

App Development Video Tutorials

Make Cross-Platform Apps with Qt: V-Play Apps

How to Add In-App Chat or Gamification Features to Your Mobile App

How to Make a Mobile App with Qt Quick Designer (QML Designer) & V-Play

  The post How to avoid C++ models in Qt and why you should care appeared first on V-Play Engine.

How to avoid C++ models in Qt and why you should care published first on https://medium.com/@TheTruthSpy

[gizmorati]

You can now try Facebook’s Relay data-fetching framework in your own apps

You can now try Facebook’s Relay data-fetching framework in your own apps At gizmorati.com, the privacy of our visitors is of extreme importance to us (See this article to learn more about Privacy Policies.). This privacy policy document outlines the types of personal information is received and collected by gizmorati.com and how it is used. Log FilesLike many other... http://gizmorati.com/2015/08/12/you-can-now-try-facebooks-relay-data-fetching-framework-in-your-own-apps/

[alphapeeler]

Google Firebase is a Google-backed app development software that enables the development of iOS, Android and Web apps. Firebase provides tools for tracking analytics, reporting and fixing app crashes, creating marketing and product experiments.

In the 5th session of the Flutter app Bootcamp, we unveil a very critical component of Flutter: “Connection to Firebase”. All these services are ten times as fascinating as they are unique. In this edition of the Flutter workshops, you’re going to develop a thorough understanding of databases and learn Firebase features such as CRUD operations, uploading images and authenticating users.

So make sure you become a part of this as the session is going to challenge your mind in the best way that it can be challenged.

🕘 Wednesday, December 8, 2021 from 11:00 AM – 12:00 PM GMT+0500.

Venue: Lab 11 (Main Campus - FAST NUCES, Karachi)

Register here: https://tinyurl.com/GDSCApp04

Stream the session live at: http://meet.google.com/frb-pzxs-ngz

#appdevelopment #flutter #flutterdeveloper #flutterdev #firebase #database #flutterapp #flutterappdevelopment #APIs #datafetching #mobileapp #mobileappdevelopment #mobileapplication #hybridapp #HybridApplication #hybridappdevelopment #softwaredevelopment #googledevelopersstudentclub #gdsc #googledevelopers #googledeveloper #GoogleDevelopersGroup #FASTNUCES #FASTNU #NationalUniversity #DSCNUCES #DSCNUCESKHI #community

[ailtrahq]

Will DAOs Become Mainstream Governance Tools? Skip to the content ' ); }, success: function(data) if( jQuery('#search-input').val() =="" ) jQuery('#datafetch').html(""); return; else jQuery('#datafetch').html( data ); }); }

[alphapeeler]

Attention all programming stars! After the incredibly positive feedback and participation in the last three workshops, GDSC comes back on stage with the fourth flutter app workshop: "Fetching Data from APIs".

Following Topics will be covered in this workshop:

- What are APIs?

- Get and Post Requests

- Try Catch blocks

- COVID Live count Application

An API (Application Programming Interface) is a set of functions that allows apps to access data and interact with external software components or operating systems.

Learn how to use APIs to fetch and upload data using GET and POST requests. Explore new concepts, such as the Try catch blocks, and what is a better way to learn them than observing their implementation and execution in real-time codes.

Today, most of the apps use remote data using APIs. So, this session will be the important part for those developers who want to make their carrier in Flutter. Your participation is as always, highly encouraged and anticipated.

🕘 Wednesday, December 1, 2021 from 11:00 AM – 12:00 PM GMT+0500.

Venue: Lab 11 (Main Campus - FAST NUCES, Karachi)

Register here: https://tinyurl.com/GDSCApp03

Stream the session live at: http://meet.google.com/frb-pzxs-ngz

#appdevelopment #flutter #flutterdeveloper #flutterdev #flutterapp #flutterappdevelopment #APIs #datafetching #mobileapp #mobileappdevelopment #mobileapplication #hybridapp #HybridApplication #hybridappdevelopment #softwaredevelopment #googledevelopersstudentclub #gdsc #googledevelopers #googledeveloper #GoogleDevelopersGroup #FASTNUCES #FASTNU #NationalUniversity #DSCNUCES #DSCNUCESKHI #community