retrofit singleton kotlin
Retrofit comes with many ready-made converters. You can read my previous article from the below link. Android's MVVM Architecture in Kotlin ft. Retrofit. Maybe all you want is to parse JSON from a web service and show it in a list in your Kotlin app for Android, while still being future-proof with a library like Retrofit. The outside class is Deferred. Singleton Class in Kotlin is also called as the Singleton Object in Kotlin. For native apps, you’ll always want an array of data objects in the end to easily show it in the UI and to interact with the contents. Finally, simply start the server. Add another new Kotlin File/Class to your project and choose the type “Object”. Android Retrofit complete course in Kotlin - This is the most complete resource online for learning about Retrofit for Android developmentThis course will take you step by step, through each concept relate. Handle all the API errors at a single place in a better way. Then we can see in the getProperty variable the word “await”, this is because our Singleton class returns a Deferred object (feature or a promise in java). You can easily adapt the code to your needs – no matter if you want to create a to-do list, load weather data or a highscore list from a web service. That’s easy. In this case, launch launches a new coroutine without blocking the current thread. If it was, we take the list of items and assign it to the recycler view adapter. The rest of our app’s code can continue to run in the meantime and the app will stay responsive. Note that in the screenshot below it’s parsed and made prettier by Firefox; but it’s of course exactly the same file as our database file we provided. The text in this article is still the original. First, we use a coroutine builder. Retrofit singleton in Kotlin. It’d be possible to add further annotation, e.g., to give the properties different names than their JSON counterparts. However, the server even allows adding, updating and deleting items through standard REST calls. You are allowed to call one suspending function from within another suspending function. First, add the Kotlin-Kapt plugin at the end of your plugin list from build.gradle of your app module. More specific https://api.adviceslip.com/advice this URL returns a random advice every time you call it. The Coroutine call adapter should take care of managing the asynchronous flow. The same example was created for my previous article “How to Create Weather App Using Retrofit 2 in Android”. Coroutines must have a scope where they’re attached to. With coroutines, your asynchronous code looks almost the same as synchronous code. Digital Healthcare, Augmented Reality, Mobile Apps and more! Kapt is an annotation pre-processor. This allows us to update the UI from within the coroutine. DEV Community – A constructive and inclusive social network for software developers. Create Retrofit Singleton Class Object After installing the Retrofit library and its dependent library in the android project, create a Singleton class object with a host URL. However, it seems that the underlying libraries already take care of that. To analyze the complex return value of the function, we go from inside out: Obviously, we want Moshi to parse the JSON and return a List of PartData instances. ... An object declaration in Kotlin is the way a singleton is made in Kotlin. In this post, I will be talking about how do REST API consumption in your applications using Retrofit + Kotlin + RxJava. As usual, you have multiple options. As you remember when creating our JSON-server, it’s running at port 3000. This example will demonstrate the working of MVVM using Live data and Retrofit in Kotlin. I used a companion object for the singletons without constructor parameters. Retrofit is a great Android library to construct communication between mobile devices and Restful API. This is just one more example about how in Kotlin we can continue to use the same libraries we’ve always used in Java for Android. Example of Service being used As such, the function needs a parameter where we can send the JSON. We don’t use that here. We’re writing our app in Kotlin. Viewed 71 times 3. This will also enable us to access the web service from multiple activities. So, we should be fine keeping our own code on the Main dispatcher. We’ll talk about all the additional dependencies besides retrofit later. getInstance) is in charge to create this single object and returns always the same object. Most importantly, the new solutions now also use Jetpack View Bindings instead of Kotlin synthetics. Login. I… Essentially, it’s the magic that makes our application wait for the web server’s results, without blocking the rest of the application. Let’s get our app ready to use Retrofit. In this article, I’ll show a walk-through using many of the newest components for a modern solution: Updated on December 15th, 2020: the solution projects on GitHub have been migrated to the latest versions and dependencies. This is an example to demonstrate MVVM Architecture in Kotlin with Retrofit in Android. In the last line of the lambda, we let Retrofit create itself, based on the mapping interface to our web service. 2 Kotlin Retrofit Tutorial - Retrofit Singleton Class, #2 Kotlin Retrofit Tutorial - Retrofit Singleton Class. In this tutorial I will show you how to set up and use Retrofit. Retrofit is a well know networking library among Android Developers, so even consider it as the industry standard. The result: Moshi. In the world of Android, two libraries are commonly used: Both have some differences in how they work, and both are good choices. Java code: public class TasksLocalDataSource implements TasksDataSource { private […] Then the method who is going to create the coroutine, and also manage the call to the API: getAdviceProperty. Retrofit is a powerful HTTP client for an Android and Java built by awesome folks at Square. Examples: your web server isn’t running, or the user has no active data connection. Packages. Additionally, we create Http client that is used to make connections with the server. To run it with a real-life server, update the IP address in WebAccess.kt. This means that the function will suspend until the result is available. Retrofit includes a few ready-made adapters for RxJava and others. That’s all you need to map from JSON to Kotlin. This client will hold the needed information for the authetication. Library. Consider what you gain: a completely salable process that works for any web service. In general singletons are realized by hiding the constructor from a class and providing a static access function. Coroutines are an excellent feature which will make your life easier. Andreas Jakl is a professor @ St. Pölten University of Applied Sciences, Microsoft MVP for Windows Development and Amazon AWS Educate Cloud Ambassador. You can download the finished example code from GitHub. The easiest way to test our app is a flexible local mock web server. */, Styling Our Android Notifications (Kotlin), Analyzing my Android Apps with SonarQube + Docker. An often used library is called RxJava 2. One of the best introductory articles I’ve found about how Coroutines work was written by Joffrey Bion. As you can see, a singleton in Kotlin is fairly easy. ... to hold the singleton object. The @Body annotation makes sure this data ends up in the body of the HTTP request. As such, it’s a bad idea to tie the Retrofit client directly to an Activity. While RxJava is of course compatible, Kotlin recently added an exciting new feature: coroutines. Understanding Retrofit with Kotlin CoroutinesNow that we have worked on the project, ... Make ApiService Singleton and reuse the same instance for all the features. This example will demonstrate the working of MVVM using Live data and Retrofit in Kotlin. Thenafter come the base url, the HTTP client and an instance about the JSON API. In android applications, Retrofit makes use of OkHttp which is a low level Http client fro android created by the same company that created retrofit. When you compile the app, Moshi will add an additional, auto-generated adapter class that takes care of everything for you. The plain Java variant is easy to understand, but by far not powerful and flexible enough for a web service. In many cases, you only need HTTP GET operations. aminography. You don’t need to write tedious callbacks anymore. An excellent way to create a local web service is the JSON Server project by typicode. Clone via HTTPS Clone with Git or checkout with SVN using the repository’s web address. The port stays the same (by default 3000). As such, it’s heavily influenced by how you handle the web request’s asynchronous nature. API Client Interface with Kotlin Coroutines for Retrofit In many cases, you only need HTTP GET operations. Android's MVVM Architecture in Kotlin ft. Retrofit. In Kotlin static methods do not exist, thus this approach can not be taken. The exact structure of the class should be pre-defined in our app, so that during conversion from JSON everything can be checked and is type-safe. You’ll find a lot of heated discussions about which library is better. The only remaining task is to trigger the asynchronous web request. This means that the task can always continue, even if our activity gets destroyed. Our first data-class has a property called slip whose type is AdviceData, this type is another data class with two properties id and advice. In my opinion, the Kotlin coroutines have more flexibility, but loose some of C#’s async/await elegance. As parameter, specify the JSON file you just created. Retrofit Configured with convertors makes it easy to serialize structured data sets. In this post, I will be talking about how do REST API consumption in your applications using Retrofit + Kotlin + RxJava. The easiest solution is to use the GlobalScope. For now, we’ll test the app using the Google Android emulator. Let’s analyze the four lines of code. So first we are going to create a new package named “network” in which we are going to add two Kotlin files: In AdviceProperty.kt we are going to add the properties of the JSON in a data-class structure. Templates let you quickly answer FAQs or store snippets for re-use. the concrete implementation of the singleton is generated by an external tool or library like Retrofit and Room and its instance is retrieved using a … Videos. This is where converters come in. But when you have to start a project from scratch and make all those working together, things becomes complicated. So, to implement the Singleton pattern in our project or software, we make a singleton class. In this class, we only need one property: an instance of the API client. The main code of this lambda contains a big chain of function calls from the Retrofit builder. Kotlin and retrofit network call tutorial. eBooks. Retrofit is a REST Client for Android and Java/Kotlin by Square. I’ve updated the source code examples on GitHub to use AndroidX instead of the Android Support libraries. Contact / Imprint — Privacy Policy — Cookie Policy, on How-To: Retrofit, Moshi, Coroutines & Recycler View for REST Web Service Operations with Kotlin for Android, Download, Export or Backup Amazon Sumerian Scenes (Part 6), Computer Vision & Photo Description: Really Simple HTML / JavaScript Example, Jetpack View Bindings instead of Kotlin synthetics, previous article where we created a list with a RecyclerView, give the properties different names than their JSON counterparts, Retrofit Call Adapter for Kotlin Coroutines, single instance of the Retrofit HTTP client for a particular URL, how Coroutines work was written by Joffrey Bion, ViewModel from the Android Architecture Components. There is another singleton that takes a constructor parameter. DELETE and PUT have another specialty: they require the ID of the object to delete / modify in the HTTP URL. In this example, I'm going to use Advice Slip JSON API. If you are using view models do not forget to cancel the Job in the onClear() method. We’ve already included both as dependencies into our app. Two are most prominent: One of the main developers of Moshi apparently first created Gson, but since then left Google and felt that he’d like to create a new converter that addresses some of the issues with Gson at a very low level that essentially requires a rewrite. By default, your web server will run for the localhost address – which is fine if you use the emulator to access the server. Made with love and Ruby on Rails. But testing with a local server is a lot easier, as you have full control over both sides. Our test server doesn’t return body data in its response; so the function return value is Void. Then in AdviceApiService.kt we are going to set up our Retrofit instance. This ensures that Retrofit properly manages its connections to the web server. So, basically is a REST client for Android. With the code above, your app would handle errors returned by the web server. 06:03:14 of High Quality Videos. Best practices and libraries are well known on Android: MVP development with Kotlin using Dagger 2, Retrofit, RxAndroid and DataBinding. Kotlin has a special keyword (“object“) which can be used instead of the class keyword. Android allows many different options for accessing web services. As we used Moshi, it already performed the mapping of the JSON response to a list of class instances for us. But at some point, you need to “bridge” to the normal world. Of course, you can also go with the new Android Architecture Components and use ViewModels and LiveData to access the web service via RetroFit. ... @Singleton will force that only one instance of the dependency will be created and used across the entire app. Question or issue of Kotlin Programming: I am trying to convert an Android app from Java to Kotlin. So, let’s launch the coroutine from a function. As you can see here, we have coroutineScope.launch this block of code allows us to create a new coroutine and run it in the thread we define previously. I won’t go into too much detail here; we’ll just use them. 2019-04-20 11:16. if you want to pass a parameter to the singleton in an easier way I think this is better and shorter. The first one is the Job which is gonna define the lifecycle of the coroutine scope. Updated on July 4th, 2019: Google is transitioning the additional libraries to AndroidX. You can choose from basic Java-style HTML requests, or go up to full-scale MVVM design patterns with the new Android Architecture Components. As such, a slightly better solution would be to use the ViewModel from the Android Architecture Components. Build your project and now we are ready to start. This completes the singleton creation of Retrofit with Kotlin! Because of that, Kotlin includes native support for Singleton-like code. But that’s a different story . In most cases, this is important to have as well; after all, you need to know if the request was successful. It defines a job that has a result. Ask Question Asked 1 month ago. The list is wrapped in a Response class. In this blog, we will learn how to make a singleton class in Kotlin? Our project should only have a single instance of the Retrofit HTTP client for a particular URL. Mvvm stands for model view view-model pattern which helps to separate development of graphic user interface and removelots of bboilerplatecodes. We also need a nice and easy way to map the server’s interface to Kotlin functions. Retrofit uses the Okhttp library for for HTTP requests. However, it’d still still crash for more fundamental errors. The difficult part is the mapping between JSON and our own class. Dispatchers.Main is specific to the Android Coroutines extensions. 49 Lectures POST (adds a new item) additionally needs a request body: the complete JSON of the new item which we send to the web server. By default, the magic number where the emulator maps your computer’s localhost to the emulator is 10.0.2.2. First of all, what is Retrofit? A singleton class is a class that is defined in such a way that only one … This part sits right at the connection between the web service and the rest of your app. Even Google uses it in their code samples. Android Architecture: Hilt, MVVM, Kotlin Coroutines, Live Data, Room and Retrofit (ft. Rick and Morty) Santiago Beroch. It’s still at version 0.9.2, but I expect this approach to be the future for using asynchronous code in Kotlin. The .isInitialized Kotlin property returns true if the lateinit property (INSTANCE in this example) has been assigned a … Call it db.json and store it to an empty directory. Moshi has great Kotlin support as well as compile-time code generation to make apps faster and smaller. "org.jetbrains.kotlinx:kotlinx-coroutines-core:$version_kotlin_coroutines", "org.jetbrains.kotlinx:kotlinx-coroutines-android:$version_kotlin_coroutines", "com.jakewharton.retrofit:retrofit2-kotlin-coroutines-adapter:$version_retrofit_coroutines_adapter", "com.squareup.retrofit2:retrofit:$version_retrofit", "com.squareup.retrofit2:converter-moshi:$version_retrofit", "com.squareup.moshi:moshi:$version_moshi", "com.squareup.moshi:moshi-kotlin:$version_moshi", com.jakewharton.retrofit2.adapter.kotlin.coroutines.CoroutineCallAdapterFactory, com.squareup.moshi.kotlin.reflect.KotlinJsonAdapterFactory, retrofit2.converter.moshi.MoshiConverterFactory, /* Moshi Makes it easy to parse JSON into objects, //Then we are going to create the interface, /* Singleton to create this instance only once, and get it ready every time we call it. For normal GET requests to retrieve data from a web service, we use the @GET annotation in front of the function definition. This static access function (e.g. To create a Singleton in Java, you’d need to write the corresponding code yourself. One of the lines in the dependencies section that we added before triggers the code generation during compilation. As parameter, we specify the dispatcher. add The Kotlin koin to your project. Essentially, the aim is always to make asynchronous calls easier than in standard Java. It’ll allow us to add annotations to our Kotlin data class to help Moshi with converting the code to JSON and vice versa: Next, add the required dependencies to build.gradle of your app module. Nothing changes in terms of behavior with regards to our example. The second one is our coroutineScope, here we define in which thread our coroutine is going to run. Like the next example: As you can see, we follow our JSON structure. So Let's Get Started: So, basically is a REST client for Android. You can download the starter project. When that URL is called, the service expects to get a JSON with all the data Moshi needs to transform it to a list of instances of our PartData class. Below the MarsApiService interface, define a public object called MarsApi to initialize the Retrofit service. Just follow the steps and you will be able to try out the same in your Android Studio as well. First, we add the base URL of the web service. Copyright 2017-2020 Andreas Jakl Note that it’s configured to run in the emulator with the local test server created at the beginning of the article. As such, within the emulator, 127.0.0.1 points to the emulator itself. We're a place where coders share, stay up-to-date and grow their careers. From my experience, Retrofit seems to be more widely used in general. This blog, I will show you how to use Kotlin and Retrofit to read data from a server. Your source code will look entirely different depending on what approach you chose – so it’s important to make a good choice right at the beginning. Just follow the steps and you will be able to try out the same in your Android Studio as well. Let’s start with the GET request to retrieve the list of items from the web service. Create base classes such as BaseActivity. On Android, coroutines help to manage long-running tasks that might otherwise block the main thread and cause your app to become unresponsive. As a bonus, it’d be great if you could also perform CRUD operations (create, read, update, delete) with the data. Typically for JSON we uses Gson convertors to serialization and De-serialization process. I also added a log message in the code above, so that you can check and see when exactly this code gets executed while your app is running. This is from Retrofit and provides full access to the server’s HTTP response. Now, let's take a look at a basic implementation, First, we need to add some dependencies to our project. It helps us to get and upload data throughout a REST API. Then, you’d launch the server with: You can try accessing your server from your phone through its web browser and your computer’s IP. The db.json fill will always be updated accordingly. But for simplicity, we’ll stick with the same names; so, don’t need any further mappings. Next, we tell Retrofit which Converter and Call Adapter to use. As its web site says is A type-safe HTTP client for Android and Java (We are going to use Kotlin...). Singleton Class. Each of these is provided as a normal Kotlin function. It returns a reference to a Job, which would allow us to cancel the running coroutine. The code for the other three CRUD operations are comparable, with some minor details changed. And you could potentially endlessly load items thanks to the efficiency of the RecyclerView. But for native code, we’d like more control. Here is the complete data class to store an item id and an item name. DEV Community © 2016 - 2021. Another good example was posted by Okta , which uses RxJava and Gson instead of Kotlin Coroutines and Moshi. It creates a new coroutine and launches it from a normal function. Active 1 month ago. We’re building on the previous article where we created a list with a RecyclerView and then added a click listener. Contrary to a class, an object can’t have any constructor, but init blocks are allowed if some initialization code is needed.. object SomeSingleton {init {println("init complete")}} We strive for transparency and don't collect excess data. Other than learning the general network call related info… This is a standard Kotlin code pattern to use when creating a service object. For example, in some cases you’d like the property to be called differently than the item’s name in JSON. The sample scenario is an item management software for an imaginary factory. In Kotlin, the singleton pattern is used as a replacement for static members and fields that don’t exist in that programming language. Note that we could switch to the IO context for blocking network operations for this call. First, check your address using ipconfig from a Powershell window. The main reason why I chose Retrofit for this tutorial: Google is also using it in the sample code for their newest Architecture Components. Retrofit is a very popular networking library by the good folks at Square, and it is widely used in the dev community. Again, Moshi takes care of the conversion; so we simply work with the Kotlin classes. Here, I have created a Weather App to demonstrate Retrofit 2 with Kotlin. Mapping the JSON isn’t enough for accessing a web service. This is an example to demonstrate MVVM Architecture in Kotlin with Retrofit in Android. For this, we use Kotlin Coroutines. Square.io You can check out all the available dependencies here on this link.For the article, we only need to add the following dependencies in our app-level build.gralde which just one line of code. Instead of using the “class” keyword, you define it with “object”. But it’s generic. Next, we check if the web request was successful. You can configure Retrofit to store a copy of every network result locally. It makes it relatively easy to retrieve and upload JSON (or other structured data) via a REST-based web service. It’s still at version 0.9.2, but I expect this approach to be the future for using asynchronous code in Kotlin. There are many reasons why it is so popular, great support for REST API's, easily testable, easy to set and make network calls. It might help if you open the powershell window with administrator rights. JavaScript directly converts JSON to classes. Small example project demonstrating how to use Retrofit for Android in Kotlin. I am struggling to translate this retrofit class into Kotlin. Google also provides a long Coroutine Code Lab. You can read more about coroutines in the Kotlin documentation. These kinds of errors are thrown with an IOException. This could also be a problem if there’s an error in the task and it gets orphaned. This keyword will take care, that only one instance of this class is created. To access it from a mobile phone in the same local network, launch json-server using your computer’s IP address. A more specific example for Android was posted on StackOverflow by Marko Topolnik. Jake Warthon, one of the most prominent Android developers, also created a Retrofit Call Adapter for Kotlin Coroutines. So Let's Get Started: This means that we use retrofit to make network calls from our applications. Moshi is our JSON to Kotlin converter. It runs our code on the UI thread. Retrofit is a networking library used to implement a type-safe REST client for Android. A better approach is the new LiveData component, which is livecycle-aware. Especially with Android’s lifecycle, the class would be re-created every time you rotate the display. Plus, it’s thread-safe! There are multiple dependencies available for koin. Now, open this directory with the command line. A singleton is created by simply declaring an object.. object SomeSingleton. Just add a single annotation before the class declaration. However, in this article I’d like to show you all four possible CRUD operations that are possible with web services: Add a new file to the project, this time of type interface. Using the activity itself is problematic: rotating the screen would pull the scope away under a running asynchronous task, due to the re-created activity. It is much less code than we use to write with java or without coroutines. So in the ViewModel (this can be your class), I have a variable named _properties which is going to store my data, you can see its type it's AdviceProperty (Remember our class in the network package). So if its children fail, its gonna notify the parent and it will cancel the other children in case we have more instances running. Our code is short and concise. For example, your computer’s local IP could be 10.2.1.205. Afterwards, it will just return the created instance. Follow. I'm using the MVVM Architecture, which means for each fragment/activity I have a ViewModel Class in which I manage all the data for my app, and also this API call. However, as ViewModels require a more significant change in our code, the GlobalScope is OK for simple web requests like in our case, and to get started with coroutines. So let’s give Moshi a try. First in this chapter, we will create an interface for the Json API and there we will define the relative URL endpoint for the POST request and the needed arguments.. Then, we are going to create a singleton client for Retrofit. This is coming from the Kotlin Coroutines. Our UI interface listener was not set up with a suspend keyword; as such, it can not suspend in the middle of the function. With you every step of your journey. It’s easy to make mistakes if you take multi-threading into account. Surround the actual web service call with try/catch to inform the user about the issue. As its web site says is A type-safe HTTP client for Android and Java ( We are going to use Kotlin...). It makes asynchronous programming a native language feature – with a syntax that is a bit like how C# handles async calls. As mentioned at the beginning, there are many alternatives of how you could implement this scenario. Each line defines a different operation: GET, POST, DELETE and PUT. It’s marked in the path definition. It might be overwhelming to choose the best way to access a web service from your Android app. #Kotlin #Android Retrofit2 singleton instance sample - TmdbApi.kt. We used the suspend functionality when we set up the interface through the Deferred type. So, let’s get started. Type the following to install the json-server module into a shared location through the npm package manager. We have now our response in a variable and we can use it wherever we want. Retrofit is a library that greatly simplifies doing requests to an API, and in this case I’m going to teach you how to integrate it with some LastFM API requests.You can see the full code working in the Bandhook Kotlin repository. With await added to the call of getPartsAsync(), we suspend execution of the lambda until the webResponse results are in. Subscription Includes. Gradle setup We will be adding the following dependencies to our build.gradle - android architecture components, kotlin extensions for activity and fragments, and retrofit + okhttp Here, I also supply together the actual code example. And that’s it! First, make sure you have Node.js installed. This would ensure the networking code doesn’t get executed on the UI thread. Jake Warthon, one of the most prominent Android developers, also created a Retrofit Call Adapter for Kotlin Coroutines. Kotlin-Retrofit. What is retrofit This is a rest client library for java and android. Here are some simple functions to trigger these operations: While you need to be aware of a lot of concepts, the actual amount of code to elegantly access a web service is minimal. // kotlin based dependency injection koin implementation 'org.koin:koin-androidx-viewmodel:2.0.1' It helps us to get and upload data throughout a REST API. An additional @Path annotation tells the library which parameter should be used for the path.