Android find view from context

No More findViewById

One of the little-known features of developing an Android application with Android Studio is data binding. With it comes many excellent features that I’ll be covering in future articles, but the most basic thing you get is elimination of findViewById.

Isn’t this just a pain in the neck?

There are tools available whose main job is to eliminate this small bit of code, but now there is an official way with Android Studio 1.5 and higher.

First, you must edit your Application’s build.gradle file and add the following into the android block:

The next thing is to change the layout file by making the outer tag instead of whatever ViewGroup you use:

The layout tag tells Android Studio that this layout should take the extra processing during compilation time to find all the interesting Views and note them for the next step. All layouts without that outer layout tag will not get the extra processing step, so you can sprinkle these into new projects wherever you like without changing anything in the rest of your application.

The next thing you have to do is to tell it to load your layout file differently at runtime. Because this works all the way back to the Eclaire release, there is no reliance on new framework changes to load these preprocessed layout files. Therefore, you do have to make a slight change to your loading procedure.

From an Activity, instead of:

You load it like this:

Here you can see that a class, HelloWorldBinding was generated for the hello_world.xml layout file and the View with the ID “@+id/hello” was assigned to a final field hello that you can use. No casting, no findViewById.

It turns out that this mechanism for accessing views is not only much easier than findViewById, but can also be faster! The binding process makes a single pass on all Views in the layout to assign the views to the fields. When you run findViewById, the view hierarchy is walked each time to find it.

One thing you will see is that it camel-casifies your variable names (just like hello_world.xml becomes the class HelloWorldBinding), so if you gave it the ID “@+id/hello_text” then the field name would be helloText.

When you’re inflating your layouts for RecyclerView, ViewPager, or other things that aren’t setting the Activity contents, you’ll want to use the generated type-safe methods on the generated class. There are several versions that match the LayoutInflater, so use the one that is most appropriate for your use. For example:

If you aren’t attaching the inflated View to the containing ViewGroup, you’ll have to get access to the inflated View hierarchy. You can do this from the getRoot() method of the binding:

Now, you may be wondering, what if I have a layout with different configurations with some differing Views? The layout preprocessing and runtime inflation stages take care of this for you by adding all View IDs to the generated class and just sets them to null if they aren’t in the inflated layout.

Pretty magical, huh? The best part about this is that there is no reflection or any other high-cost techniques used at runtime. It is very easy to sprinkle this into your current applications to make your life just a little bit easier and your layouts may load just a tiny bit faster.

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Different ways to get Context in Android

Context is one of the important and most used property. You need Context to perform a lot of things on Android. Be is displaying a toast or Accessing database, you use context a lot while building Android app.

Context is property, well, which can give you the context of whats happening on the Screen/Activity it belongs to. It contains information about what Views are there, How they are laid out etc.

So, it is important to know different types of Context and methods you can call to get context. Lets get started.

The “this” Keyword

The this keyword in general sense refers to current class instance. So, when use “this” keyword inside an Activity, it refers to that Activity instance. And as Activity is subclass of “Context”, you will get context of that activity.

If you are not directly inside Activity, for example inside an OnClickListener, you can get the current context by referencing with Activity name like MainActivity.this (Java) or this@MainActivity (Kotlin)

Get current activity context : View.getContext()

This method can be called on a View like textView.getContext() . This will give the context of activity in which the view is currently hosted in.

Get App-level context : getApplicationContext()

If you need to access resources which are out of scope of specific activity, like when accessing SharedPreferences, displaying Toast message etc. you can use this.

So unlike activity context, which will be destroyed when close an activity, Application Context the application wide context which won’t get destroyed until you completely close application.

You can directly access application context by calling getApplicationContext() or by calling on activity context like context.getApplicationContext()

Get Original context : getBaseContext()

This method is only useful when you are using ContextWrapper. You can get the original context which was wrapped by ContextWrapper by calling contextWrapper.getBaseContext()

( ContextWrapper is a wrapper class, using which you can override any method of Context, while still retaining the original context)

Get Context from Fragment : getContext()

When you call getContext() from an Fragment, you will get the context of the activity in which that fragment is hosted in.

Get parent Activity : getActivity()

You can get the parent activity from a Fragment by calling getActivity() .

💡Difference : Both getContext() and getActivity() are not much different in most cases, when you just need a context as both will get Parent activity context. Except for some cases, for example when using ContextWrapper, getContext() and getActivity() can point to different contexts.

Non-nullable Context : requireContext() and requireActivity()

These methods are same but “NotNull” versions of getContext() and getActivity() respectively. Usually, if a fragment is detached from Activity, you will get “null” value when you call getContext() or getActivity() . So even when you are sure the context won’t be null, you still have to add null checks (especially in Kotlin) because they return Nullable type.

But requireContext() and requireActivity() will throw IllegalStateException instead of returning null, if there is no context.

These methods are mainly useful when you using Kotlin and you need a Non-Nullable Context. So using these methods instead, is matter of personal preference.

So, did you learn something new? If you did, please clap and share the post. 😄

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Evolution of Finding Views by ID in Android

The findViewById() vs Butterknife vs Kotlin Synthetics vs DataBinding vs ViewBindings

For more than a decade, Android developers have struggled with a simple but annoying issue. Getting the view reference from XML layouts to their view classes such as Activity or Fragments in entirely separate language — Java or Kotlin.

As a beginner in Android, I used to get confused a lot. The Android SDK provided a method: findViewById() . Functionality-wise, this method performs a singular task — it will give you the reference to the view in XML layouts by searching its ID. And if nothing is found, it will give you the good old NULL , which is said to be the 1-billion dollar mistake by its creator.

In this article, I am going to discuss on how the findViewById() evolved over time and what’s the best approach in “modern Android development” to get the view reference from XML layouts.

The findViewById() method

Obviously, the first one is the findViewById() method. Introduced in the API level 1, this requires an ID and returns a View object.

There are some problems with this approach.

If there is view with this ID in this layout, you won’t get any compile time errors. Rather you will get NullPointerException at runtime when Android fails to locate the view in Activity , Fragment or ViewGroup .

If the view is TextView in XML layout and you are type-casting it as Button , you won’t get any compile time errors. Instead you will get ClassCastException as a TextView cannot be converted to Button .

This method was used extensively and is being used as well throughout whole evolution of Android SDK. In the API level 26 of compileSdk , the definition of this method was slightly changed to remove the casting issue.

Now, developers don’t need to cast their views manually in the code. If you are referencing a Button with a TextView ID, then Android SDK will try to find the Button with the provided ID and it will return NULL because it won’t be able to find it.

But in Kotlin, you would still need to provide the type like findViewById

(R.id.txtUsername) . This may give you NullPointerException if you are not checking your views for null-safety, but this method will not throw ClassCastException like it used to.

Analysis

Type-safe: Before API 26, there was no type-safety.

Null-safe: No null-safety. You will have to check views before accessing for null values.

Boilerplate Code: A lot. You have to declare a separate variable for all the views you need from XML layouts.

Build-time: No difference in build time.

Languages: Supports both Java and Kotlin.

Butterknife

Many different libraries have tried to simplify the findViewById() usage with different methods. Particularly, the Butterknife library created by Jake Wharton has become super famous and has got huge interest by developers around the world. It has become to sort-of standard way to avoid the findViewById usage.

The library uses annotation-processing and fetches the views from XML layouts using the findViewById method under the hood through code generation. It’s very easy to use, and helps in reducing the boilerplate code for developers.

It has almost similar issues as findViewById . However, it adds a null-safety check at runtime to avoid the NullPointerException .

Attention: This tool is now deprecated. Please switch to view binding. Existing versions will continue to work, obviously, but only critical bug fixes for integration with AGP will be considered. Feature development and general bug fixes have stopped. —** Source: Butterknife Github repository**

Analysis

Type-safe: No type-safety as it uses findViewById .

Null-safe: The library checks the views for null-ability at runtime before accessing.

Boilerplate Code: Reduces the boilerplate as annotation processors auto generate code for you.

Build-time: Build time is affected because of annotation processing.

Languages: Supports both Java and Kotlin.

Kotlin Synthetics

Android SDK is now the Kotlin-first officially. That means that Android SDK will implement APIs from the Kotlin language perspective first and later these will be added for Java.

One of the biggest features Kotlin introduced is Kotlin Extension Methods. And with the help of it, Kotlin Synthetics came into existence. Kotlin Synthetics provides developers direct access to their views from XML layout through the auto-generated Kotlin extension methods.

Kotlin Synthetics calls findViewById method once and then caches the view instances in a HashMap by default. This cache configuration can be changed to SparseArray or no cache via the Gradle settings.

Overall, Kotlin Synthetics is a good option as it is type-safe and requires null check through Kotlin’s ? operator if the view is present only in some layout configurations. It requires no extra code from the developers. But this is only supported for Kotlin projects.

But there’s a slight problem which lots of developers have faced with using Kotlin Synthetics. For example, if you set your content view to a layout, then type an ID that only exists in a different layout, the IDE lets you autocomplete and add the new import statement. Unless the developer specifically checks to make sure their import statements only import the correct views, there is no safe way to verify that this won’t cause a runtime issue.

Analysis

Type-safe: Absolutely

Null-safe: Normally its null safe. But if view ID is also present / missing in other layouts, then it requires developer to explicitly either use safe call operator ? or check the variable before use. Developers can use view from other layout leading to NullPointerException .

Boilerplate Code: No boilerplate code as extension methods are generated. It only requires to apply android-kotlin-extension plugin in the build.gradle one time.

Build-time: No difference.

Languages: Supports only Kotlin.

Data Binding

Data Binding Library is a support library that enables you to bind UI elements in your layouts to data sources in your app using a declarative style rather than programmatically.

The Data Binding is much superior in terms of functionality from other approaches as it not only gives you the type-safe AND null-safe view references but also allows you to map your data with views directly inside the XML layouts.

You will have to manually convert layouts to support data binding by nesting in tag.

Now, Android Studio will generate classes for your layouts. For example, if your layout file name is activity_main.xml , then Android will generate a class ActivityMainBinding either in Java or Kotlin as per your preferences. You can use that to access the views without any NullPointerException or ClassCastException .

The best advantage of using Data Binding is that it allows developers to map data with the views in XML without even accessing those in the Java/Kotlin files. You can also use two-way binding to update your XML or data value without any listeners or callbacks.

Analysis

Type-safe: Absolutely

Null-safe: Absolutely

Boilerplate Code: Requires each layout file to be nested inside tag. And also you will have to create instance of auto generated binding class and inflate it to your Activity or Fragment .

Build-time: Increases build time as it generates class files of layouts. Often time, it’s slow because you will have to manually press “Make” button to update / generate new classes for your layouts.

Languages: Supports both Java and Kotlin.

View Binding

The ViewBinding introduced in Android Studio 3.6 recently is sort-of subset of the Data Binding library. It improves build times because no annotation processing is required. It doesn’t require any extra attention to layout files by nesting those in tags. It simply works on all layout files by default.

The only difference with data binding of this is that this is only used for view references. It doesn’t do any data mapping or two-way data binding.

You can use ViewBinding in place of other options if you are simply looking for a good approach to get views from layout files.

This only works on Android Studio 3.6 or later versions. You can enable it by adding this in your app’s build.gradle file.

Then Android Studio will generate View Binding classes for all your layout files. You can use those classes to inflate in the Activity or Fragments just like you would do in Data Binding.

If you want some layout file to be skipped for view binding class, you can do so by adding tools:viewBindingIgnore=»true» in your layout files.

Analysis

Type-safe: Absolutely

Null-safe: Absolutely

Boilerplate Code: No boilerplate code as View Binding classes are generated automatically. It only requires enable the View Binding in the build.gradle one time.

Build-time: No impact on build speed. View Binding* is designed to solve the performance issue connected to using Data Binding *so it doesn’t have a negative impact on the build speed.

Languages: Supports both Java and Kotlin.

Time to Make a Decision

Looking at all the options and their analysis, View Binding is the best option at this time to use.

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