![]() Time to write your first annotation processor! First, repeat the drill with adding a new Kotlin library module to the project: This continues until the processor processes all the new files. If this round generates any new files, another round starts with the generated files as its input. The first round starts when the compilation reaches the pre-compile phase. It can create new source files however, it can’t modify existing ones. ![]() Annotation processing is a tool built into javac for scanning and processing annotations at compile time.These points should bring you up to speed without going in-depth: Here’s a quick breakdown of the core concepts. That is, less code (annotations) magically turns into more functionality, and the catalyst for this computational alchemy is annotation processing. The topic of annotation usage and consumption is broad and deep, yet it boils down to doing more with less. Its sole parameter specifies the ID of the view that the annotated property should bind to.It only needs to be around during the compilation phase.Unlike AdapterModel, this one will exclusively target properties.This annotation has the same anatomy as the previous one. Replace the default class declaration with the // // 2Īnnotation class ViewHolderBinding(val viewId: Int) // 3 Add another class to autoadapter.annotations, and name it ViewHolderBinding.kt. You need one more annotation to specify how model fields map to views. Update the declaration like this:Īnnotation class AdapterModel(val layoutId: Int) The AdapterModel annotation needs a single parameter, the ViewHolder layout ID. These allow you to add even more information and fine-tune an annotation’s usage. With the SOURCE retention that you’re using for AdapterModel, the annotation won’t make it into the compiled code at all. If you use runtime retention on an annotation, you’ll be able to query for it using reflection. You’ll only use AdapterModel on classes, so add the following code above its second common annotation class is It tells the compiler how long the annotation should “live.” AdapterModel only needs to be there during the source compilation phase, so you should add this below the Another popular value for is RUNTIME. In other words, it tells which code elements you can place this annotation on. The first common annotation class is It describes the contexts in which an annotation type is applicable. Exploring Annotation AnatomyĮven when writing a simple annotation, you can’t go without using other annotations on it! You’ll annotate your annotation classes with two common annotations - yep, that’s an alliterative mouthful. That’s it! You can now type elsewhere in the code to annotate other code elements. You just need to put the annotation keyword in front of the class. Then open AdapterModel.kt, which you’ll find in your newly created module!Ĭurrently, AdapterModel is a normal Kotlin class, but turning it into an annotation class is simple. Make sure Kotlin is selected as the language.Name the module autoadapter-annotations.Select File ▸ New ▸ New Module…, and then scroll down to select Java or Kotlin library. It’s common practice to hold annotations and processors in separate modules - though that’s not a requirement by any means. Your first step is to create a new module to hold your annotations. ![]() This annotation processor will automatically generate the adapter for the RecyclerView in MainActivity based on annotating Person. Your mission - should you choose to accept it - is to write an annotation processor. It defines a simple person model with a name and an address: MainActivity.kt contains the sole Activity containing a RecyclerView. ![]() Open the starter project to find a small app named AutoAdapter. Use the Download Materials button at the top or bottom of this tutorial to download the starter project. If you’re also new to Android development, check out the Getting Started with Android tutorials. If you’re unfamiliar with Kotlin, take a look at this tutorial. Note: This tutorial assumes you have previous experience developing for Android in Kotlin. ![]()
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