Why Are Kotlin Synthetics Deprecated and What Are the Alternatives?

Why Are Kotlin Synthetics Deprecated and What Are the Alternatives?

Comparing which one to use: findViewById vs. Kotlin Synthetics vs. data binding vs. view binding

Recently Android has announced that with Kotlin 1.4.20, their Android Kotlin Extensions Gradle plugin will be deprecated and will no longer be shipped in the future Kotlin releases.

Android Kotlin Extensions plugin brought with it two very cool features :

  • Synthetics let you replace calls to findViewById with kotlinx.android.synthetic bindings.
  • Parcelize allows you to remove boilerplate and easily create Parcelables through the @Parcelize annotation.

And with the deprecation of this plugin, we will no longer be able to use these features. Don’t worry about Parcelize, as it will be now shipped as a standalone plugin: kotlin-parcelize. But this is definitely going to be the end for Kotlin Synthetics.

Now Android developers all across the globe, have, with a very heavy heart, to say goodbye to Kotlin Synthetics. But first, let's understand why Kotlin Synthetics was introduced in the first place, why it’s deprecated now, and what the options are for us apart from it.

“Necessity is the mother of invention”

History — findViewById

Earlier, to get the IDs of views, we were dependent upon findViewById.

This method looks very simple, but there were a lot of issues with this that developers were facing.

This function works by traversing the view hierarchy to find a widget with the ID you specified. It returns the view as soon as it is found or it returns null if it is not present. Let's discuss some of the issues with this approach:

  1. By looking at how it works above, we can say that this method is costly. Developers would use it exhaustively at runtime, especially in the earlier implementations of list view’s adapter, and it made their code perform poorly.
  2. If your view is not present in the layout, you will get NullPointerException at the runtime, i.e., not null safe.
  3. Prior to Android API 26, it returned the view (parent class) which you have to manually type cast, and a wrong cast would lead to ClassCastException, i.e., not type safe.
  4. A lot of boilerplate code. You have to write the same method for all your views, type cast them, and then assign them to a variable.

Then libraries like Butter Knife came along to make this approach simpler. Butter Knife improves the issue of boilerplate code partially but still has not solved issues with type safety and null safety. Moreover, it used annotation processing which did slow down the build time a bit. (Note: Butter Knife is now deprecated.)

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