View binding android studio fragment kotlin

View Binding in Android

We have learnt that every time we need to access a view from our XML layout into our Java or Kotlin code, we must use findViewById(). It was okay for small/personal projects where we use 5 to 6 views in a layout. But for larger projects we have comparatively more views in a layout, and accessing each view using the same findViewById() is not really comfortable.

What is View Binding?

View binding is a feature that allows you to more easily write code that interacts with views. Once view binding is enabled in a module, it generates a binding class for each XML layout file present in that module

Simply put, this allows us to access the views from the layout file in a very simple way by linking variables of our Kotlin or Java code with the XML views. When a layout is inflated, it creates a Binding object, which contains all the XML views that are casted to the correct type. This makes it really easier for us since we can retrieve all views in one line of code.

Getting started with View Binding

1. Let’s start by enabling view binding in our project:

In build.gradle(:app) add the code in -> android

2. Before the onCreate() method, we create our binding object

3. Perform the following steps in onCreate() method:

• Call the inflate() method to create an instance of the binding class for the activity to use.
• Get reference to the root view
• Pass the root view to setContentView() [setContentView(binding.root)] instead of layout [setContentView(R.id.activity_main)]

4. To get reference of any view, we can use the binding object:

Using View Binding in Fragments

We follow the same steps:

1. Before the onCreateView() method, we create our binding object

2. Initialize our binding object in onCreateView()

3. To get reference of any view, we can use the binding object

Note: The name of the binding class is generated by converting the name of the XML file to camel case and adding the word “Binding” to the end. Similarly, the reference for each view is generated by removing underscores and converting the view name to camel case . For example, activity_main.xml becomes ActivityMainBinding, and you can access @id/text_view as binding.textView.

View binding has important advantages over using findViewById():

• Null safety: Since view binding creates direct references to views, there’s no risk of a null pointer exception due to an invalid view ID.
• Type safety: The fields in each binding class have types matching the views they reference in the XML file. This means that there’s no risk of a class cast exception.

Start using View Binding

If you’re intrigued by View Binding and want to learn more about it, here’s some resources for you to learn:

One-Liner ViewBinding Library

You would have noticed that to use View Binding, we need to call the static inflate() method included in the generated binding class ( which creates an instance of the binding class for the activity or fragment )

Yesterday I came across an awesome library that makes ViewBinding one-liner ( By removing the boilerplate code and easily set ViewBindings with a single line )

One-liner ViewBinding Library : [Click Here]

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Делаем Android View Binding удобным c Kotlin

Привет! Меня зовут Кирилл Розов. Я автор Telegram канала Android Broadcast. Очень люблю Kotlin и мне нравится с помощью его возможностей упрощать разработку. С такой задачей я недавно столкнулся, когда на новом Android проекте начали использовать View Binding.

Эта возможность появилась в Android Studio 3.6, но на самом деле она не совсем новая, а облегченный вариант Android Data Binding. Зачем столько усложнений? Проблема была в скорости — множество разработчиков использовали Android Data Binding только для генерации кода со ссылками на View и игнорировали другие возможности библиотеки. Чтобы ускорить генерацию кода, создали View Binding . Однако стандартный способ работы с ней — это дублирование кода от которого хочется избавиться.

Стандартный способ работы с View Binding

Разберем работу View Binding на примере Fragment. У нас есть layout ресурс с именем profile.xml (содержимое его неважно). Если мы хотим использовать ViewBinding, тогда в стандартном варианте это будет выглядеть так:

Проблема здесь несколько:

• Много лишнего кода
• Копи паста: каждый Fragment будет иметь аналогичный кусок кода
• Property viewBinding получается nullable и модифицируемым.

Давайте пробовать избавляться от этого с помощью Cилы Kotlin

Kotlin Delegated Property в бой

С помощью делегирования работы с property в Kotlin можно круто повторно использовать код и упростить некоторые задачи. Например, я применил это в случае с ViewBinding . Для этого я сделал свой делегат, который оборачивает создание ViewBinding и очистку его в нужный момент жизненного цикла:

и конечно же функцию-фабрику, чтобы не видеть как делегат создается:

После небольшого рефакторинга с новыми возможностями я получил следующее:

Вроде задача, которая ставилась, была достигнута. Что же могло пойти не так?

Момент, когда что-то пошло не так.

В какой-то момент возникла необходимость чистить View следующим образом:

Но в итоге я получил состояние, что моя ссылка на ViewBinding внутри делегируемого property уже была почищена. Попытка перенести очистку кода до вызова super.onDestroyView() не принесла успеха и я начал копаться в причинах. Виновником стала реализация вызова методов жизненного цикла у Fragment.viewLifecycleOwner .

Событие ON_DESTROY в Fragment.viewLifecycleOwner происходит до вызова Fragment.onDestroyView() , поэтому FragmentViewBindingProperty очищался раньше, чем я того ожидал. Решением стало отложить вызов операции очистки. Все вызовы жизненного цикла вызываются последовательно и на главном потоке, поэтому весь фикс свелся к откладыванию очистки с помощью Handler :

Полный код можно найти здесь и использовать его на своих проектах.

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Simple one-liner ViewBinding in Fragments and Activities with Kotlin

Feb 23, 2020 · 3 min read

There’s a new feature in Android Studio 3.6 called “view binding”. It’s just like databinding, except all it does is take your existing layout, and generate a binding for it — no changes necessary, no tags, and especially no tags. Just pure layouts!

First we enable it in our build.gradle:

Then we take our regular layout

and use it via the binding

And in Fragments, we can do something similar.

The regular way of doing this is from the ViewBinding sample.

In this article t h ough, I’m going to show you how to make it a one-liner (like in the above examples).

How to actually make it a one-liner

First we add a few Jetpack Lifecycle components to our build.gradle:

Then we learn about Kotlin read-write properties and read-only properties (and how to create custom delegates in Kotlin).

Once we know that and we’ve read the source code for AutoClearedValue, it’s quite easy to set up in Fragments. All we need to do is pass the MyBinding.bind function reference to our delegate, and initialize the View’s binding using that function. Then, we clear this binding value when the views are destroyed.

This fragment delegate is also available as a library from Jitpack.

In our Activity, we can instead use a lazy delegate that inflates the binding, as we don’t need to worry about a separate view lifecycle.

Now we can finish our original examples, and use a single-liner initialization for our view binding.

With the power of Kotlin delegates and Jetpack Lifecycle components, we have turned our ViewBinding into a single-liner.

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From Kotlin synthetics to Android ViewBinding: the definitive guide

Binding your views like a pro in 2 minutes.

Since Kotlin 1.4.20, JetBrains deprecated the kotlin-android-extensions plugin in favor of Android View Binding solution.

If you have been using this plugin, it’s time to move on before this feature is completely removed (or switch to Compose?).

For having completely refactored our Android application to use View Binding, we know that it can be somehow painful and sometimes it looks less simple with this new solution. For example, the binding of your view will have to be done differently if you’re working with an Activity or a Fragment. If your layout uses include there are some tricky ways to handle them too.

That’s why we’ve been implementing some convenient methods to make it simpler.

Setup

If you’re refactoring your whole application code, we advise you to do it module per module to avoid committing too many updates.

Enable view binding

To enable the ViewBinding feature, you just need to enable this build feature on your module build.gradle files:

Remove android extensions plugin

If you’ve been using kotlin-android-extensions before, remove the plugin from the build.gradle file too:

Don’t forget to also remove the Android Extensions experimental flag:

Parcelize annotations

The Parcelize annotations have been moved to another package & the previous one has been deprecated.

So, if you used the Kotlin Parcelize annotation to automatize the implementation of your Parcelable objects, you’ll need to use the new plugin :

Then, replace imports in your code from kotlinx.android.parcel to kotlinx.parcelize.

Activities

To set up an Activity to use your binding class you basically have to:

1- Declare a late init variable for your binding class.

2- In the onCreate method, inflate your layout using the static inflate method from the generated Binding class.

3- Call the Activity setContentView with the root view from your binding class.

We can definitely make it way shorter using some extensions:

Our viewBinding method is a simple delegate that inflates lazily the view of the activity by using the inflater method given as a parameter.

In the Activity we just need to declare the binding as a simple val property and set the content view of the activity.

Fragments

Using View Binding in Fragments is quite less easy as you have to do many things to make it works:

1. 1- Declare a var property for your binding class instance.
2. In the onCreateView callback, inflate the layout for your binding class & return the root view of it.
3. To avoid potential leaks, reset your binding class to null in the onDestroyView callback.

As per the official documentation, it should look like that:

That’s a lot of code to add & you should also pay attention to potential leaks on the binding class. This can also be disturbing as the method is quite different from using it in an Activity. Note that you also need to use the !! operator to hide the nullability of the original field.

There’s a lot of room for improvement here and I found a way better solution to deal with it in 1 line:

Yep, really simple!🚀

Here are some explanations:

1. We pass to the Fragment constructor the id of our fragment layout, which will be inflated for us.
2. We declare the binding property that will handle the fragment lifecycle work for us.

Have a look at this Gist:

Our viewBindingWithBinder simply instantiate a delegate object that will bind the view of our fragment lazily. As the Fragment already inflate the view from the layout id that we pass to it in its constructor, we just need to bind our binding class from it.

The FragmentAutoClearedValueBinding class is the one that will be responsible to clear the reference to the binding class when the fragment gets destroyed by adding an observer to its lifecycle. In the getValue method, we bind the view to our binding class the first time we access our binding property from our fragment.

ViewHolder

If you’ve been using Kotlin synthetics, you probably have something that looks like this:

You can now remove the usage of LayoutContainer and make some updates in your view holder:

Here we have simply changed our constructor to take the binding class in parameter instead of having a view object.

To instantiate your view holder, you can create a static method in a companion object:

Includes

In your layouts, you probably have views that are included in your layout using the include tag. Then, you must be aware that it can be tricky to deal with it with view binding.

With a view group

If your included view has a root view that is a ViewGroup (LinearLayout, FrameLayout, etc.) then you can set an id to the include tag in your main layout.

The generated LayoutBinding class will have a property mergeLayout of type LayoutMergeBinding that reference the layout_mege layout views.

So in an activity, you can easily reference your TextView as:

With a

If your included view uses a tag in it like in this example:

And your main layout is:

Then, the layout_merge.xml file content will be merged into your main layout. But, the binding class will not expose a property titleLbl (it will only contain your root LinearLayout ) 😭.

So, what can you do to access to your titleLbl ? You’ll need to re-bind your view with another binding class. As each layout files have its own binding class, your layout_merge layout will have a LayoutMergeBinding class generated. That’s the one we will use to retrieve our views.

From an activity, you can add another property for the 2nd binding class:

The mergeBinding property will then allow you to access the titleLbl view.

Conclusion

We hope this article was useful to you if you’re still refactoring your views to use ViewBinding or to give you some hints to refactor how you’re using it.

And you, how did you implement it into your app? Don’t hesitate to share with us your tip&tricks!

If you want to join our Bureau of Technology or any other Back Market department, take a look here, we’re hiring! 🦄

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