Free Updates. DRM Free. Write and Publish on Leanpub You can use Leanpub to easily write, publish and sell in-progress and completed ebooks and online courses! Advanced Web Application Architecture. Matthias Noback. Paul Hammant. In Java, every objects can be null by definition. So we would have to deal with a lot potentially null variables which in real life are never null. This means our code could end up with hundreds of!! For instance, something that gets an Object in Java will be represented as Any!
Luckily, latest versions of Android are starting using the Nullable and NonNullannotations to identify the parameters that can be null or the functions that can return null, and the Kotlin compiler is able to detect that and choose the appropriate translation into Kotlin language. Said that, if we are for instance overriding onCreate for an Activity, we need to mark savedInstanceState as nullable: 1 2 override fun onCreate savedInstanceState: Bundle? But there are parts of the SDK that are not properly annotated yet.
So when in doubt, you can just use a nullable object and deal with the possible null. Remember, if you use!! The logical steps would be: 1. The source of the data is an implementation detail that could easily require to be changed, so adding some extra code that abstracts the commands from the access to the data sounds like a good idea.
In our implementation, it will iterate over a list of sources until a proper result is found. It will use a database source and a server source. The order is important, because it will iterate over the sources, and the search will be stopped when any of the sources returns a valid result. The logical order is to search first locally in the database and then through the API. So, as we have access to Kotlin sources, I just copied first function and modified it to behave as expected: 1 2 3 4 5 6 7 inline fun Iterable.
It will iterate and execute the predicate over the elements in the Iterable collection. When the result of the predicate is not null, this result will be returned. If we wanted to include the case where all the sources can return null, we could have derived from firstOrNull function instead.
The difference would consist of returning null instead of throwing an exception in the last line. Some of the sources in our case the database may need it. That way, we can keep it cached into the database for future requests.
You can take a look at the provider to see the details. The overridden function makes the request to the server, converts the result to domain objects and saves them into the database. It finally returns the values from the database, because we need the row ids that were self-generated by the insert query. With these last steps, the provider is already implemented.
Now we need to start using it. The ForecastCommand no longer should interact directly with server requests, nor convert the data to the domain model. There are also new powerful ideas that will solve some particular problems much easier. If one of the branches returns Unit, the whole expression will return Unit, which can be ignored, and it will work as a regular Java if condition in that case.
Flow control and ranges This expression will try to match its argument against all possible branches sequentially until it finds one that is satisfied. It will then apply the right side of the expression. For the default option, we can add an else branch that will be executed if none of the previous conditions are satisfied. Take into consideration that when it is used as an expression, it must cover all the possible cases or implement the else branch.
But it can be many more things. We could, for instance, check the type of the argument and take decisions based on this: It works with anything that provides an iterator: There are usually simpler and more visual ways to resolve this problem. But their scope is much wider.
Ranges help simplify our code in many creative ways. For instance we can convert this: It will receive a function which uses a ForecastDataSource to return a nullable object of the generic type, and will finally return a non-nullable object. The ForecastDb will always have the required value already cached from previous requests, so we can get it from there this way: 1 2 3 override fun requestDayForecast id: Long : Forecast?
I created another utility function called byId, because a request by id is so common that a function like that simplifies the process and is easier to read. The implementation of the function is quite simple: 1 2 fun SelectQueryBuilder. This function is quite generic, but as you can see, you could create as many extension functions as you need based on the structure of your database, and hugely simplify the readability of your code.
The DbDataMapper has some slight changes not worth mentioning. You can check them in the repository. On the other hand, the ForecastServer will never be used, because the info will be always cached in the database. This is really important for functional programming, and particularly useful when dealing with edge cases with try-catch or when throwing exceptions.
For instance, the example above shows how we can assign an exception to the result even if they are not of the same type, instead of having to create a full block of code.
In Android Studio 2. You will see a Source Language dropdown at the end that you can change to Kotlin. Our detail activity will receive a couple of parameters from the main one: the forecast id and the name of the city. Overview Get Started Developer Stories. Google is committed to advancing racial equity for Black communities.
After getting some experience on such an awesome platform, he started a new adventure at a mobile company, where he led several projects for important Spanish companies. He now works as an Android Engineer at Plex2, where he also plays an important role in the design and UX of the Android applications. Your Developer Credentials 5. Privacy and Information 6. Before any of this information is collected, the SDK will notify you and seek your consent. If you withhold consent, the information will not be collected.
Third Party Applications 7. You understand that all data, content or resources which you may access through such third party applications are the sole responsibility of the person from which they originated and that Google is not liable for any loss or damage that you may experience as a result of the use or access of any of those third party applications, data, content, or resources.
You may not modify, rent, lease, loan, sell, distribute or create derivative works based on these data, content, or resources either in whole or in part unless you have been specifically given permission to do so by the relevant owners.
In that case, the License Agreement does not affect your legal relationship with these third parties. Write review. In this course, Aaron Sarazan, Lead Software Engineer at Capital One and a leading advocate for Kotlin, demonstrates how to take a basic Android app in Java and convert it to Kotlin, teaching you key features of the Kotlin programming language along the way. PDF Drive investigated dozens of problems and listed the biggest global issues facing the world today. Beginning SharePoint Development 18 June Beginning SharePoint 18 June About the author Hi!
This is Antonio Leiva. Since the end of , I am self-employed. I spend my time helping Android developers and the companies they work for to transition from Java to Kotlin.
By mastering the language, they manage to boost their productivity and create more robust and maintainable software. I am really thankful for having had the opportunity to help thousands of people with my content, which goes from my regular posts in my blog antonioleiva. I also became a Kotlin Certified Training by JetBrains, so I am proud to offer certified training, which you or your company can participate in. I have both online and live training. If you are interested in any of them, please write me to contact antonioleiva.
If you want to know a little about me, I live in Madrid, Spain. Since that, I moved from my first company to another one called Gigigo, a Spanish brand that built third-party Apps.Thank you for interesting in our services. We are a non-profit group that run this website to share documents. We need your help to maintenance this website. Please help us to share our service with your friends. Share Embed Donate. Leanpub empowers authors and publishers with the Lean Publishing process. Lean Publishing is the act of publishing an in-progress ebook using lightweight tools kotlin for android developers free download many iterations to get reader feedback, pivot until you have the right book and build traction once you do. Please help Antonio Leiva by spreading the kotlin for android developers free download about this book on Twitter! The suggested hashtag for this book is kotlinandroiddev. I felt this book as a necessary step forward. And, of course, this is specially dedicated to you. With your support and your help this book is growing, and I hope it will become a reference. So any claim or suggestion you think it will improve the quality of this gold miner game free download for pc will be welcomed. Kotlin for android developers free download this book. Is this book for you? About the author. Download PDF of Kotlin for Android Developers Learns Kotlin the easy way while developing an Android App by Antonio Leiva | PDF Free Download. Description. Kotlin for Android Developers Learn Kotlin the easy way while developing an Android App Antonio Leiva This book is for sale at. JetBrains designed Kotlin with Java developers in mind, and with IntelliJ as its Download. You can also get this PDF by using our Android Mobile App directly. Download the Kotlin for Android Developers PDF preview that includes the first chapters of the book for free. Alternatively, join the list for a free course. Kotlin is a modern statically typed programming language that will boost your tool lets you to see the equivalent Java-based code as you learn Kotlin. Download Kotlin is a free and open source project under the Apache license. Write better code, work faster, and be more productive with an intelligent code editor that provides code completion for Kotlin, Java, and C/C++ languages. Feel free to write anytime to [email protected] What is “Kotlin for Android Developers” about Throughout this book, I create an Android app from the. Kotlin is the new official language to write Android Apps, and thanks to this book, you'll be writing code in no Read Free Sample As you could read in previous pages (and probably the site were you downloaded), this is a lean publication. Take an Android app in Java and convert it to Kotlin, learning key features of the Kotlin programming language along the way. Now that you have a working app, let's recap what you've built. There are also Delete and Update annotations for deleting and updating rows, but you are not using them in this app. Why use a Repository? Search for:. As such, it doesn't matter where the data comes from. What does Kotlin code look like? Intro to TensorFlow for Deep Learning. Android Studio Android Studio provides first-class support for Kotlin. When you cancel the job of a scope, it cancels all coroutines started in that scope. Room does a lot of work for you that you used to have to do yourself. A repository class abstracts access to multiple data sources. We also use third-party cookies that help us analyze and understand how you use this website. Views and Activities and Fragments only interact with the data through the ViewModel. Safer code Improve your app quality. Learn more.