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Android Dynamic Feature Modules : The Future

In Google I/O 2018, a new publishing format was introduced by Google known as Android App Bundle(.aab). A few out of many benefits of using app bundle are dynamic delivery, automatic multi-APK distribution, smaller APK size and dynamic feature modules.

Note : For more details about App Bundle, you can refer this blog .

What is Dynamic Delivery?

Google Play uses your app bundle to generate and serve optimized APKs for each user’s device configuration, so they download only the code and resources they need to run your app. For example, a user should not get x86 libs if the device architecture is armeabi. Also, users should not get other resources like strings and drawables they are not using.

You can also convert your independent modules/features (without these modules your app is functional) into dynamic feature modules which can be downloaded later. Through Dynamic Delivery, users can then download and install app’s dynamic features on demand after they’ve already installed the base APK of your app. As a result, the initial download size of your app is less and users don’t need to have unused code/feature in their devices.

Dynamic Delivery with split APKs

Split APKs are very similar to regular APKs — they include compiled DEX bytecode, resources, and an Android manifest. However, the Android platform is able to treat multiple installed split APKs as a single app. The benefit of split APKs is the ability to break up a monolithic APK into smaller, discrete packages that are installed on a user’s device as required.

• Base APK : This APK contains code and resources that all other split APKs can access and provides the basic functionality for your app. When a user requests to download your app, this APK is downloaded and installed first. That’s because only the base APK’s manifest contains a full declaration of your app’s services, content-providers, permissions, platform version requirements, and dependencies on system features.
• Configuration APKs : Each of these APKs includes native libraries and resources for a specific screen density, CPU architecture, or language. When a user downloads your app, their device downloads and installs only the configuration APKs that target their device. Each configuration APK is a dependency of either a base APK or dynamic feature APK. That is, they are downloaded and installed along with the APK they provide code and resources for.
• Dynamic Feature APKs : Each of these APKs contains code and resources for a feature of your app that is not required when your app is first installed. That is, using the Play Core Library, dynamic APKs may be installed on demand after the base APK is installed on the device to provide additional functionality to the user.

Note : Because devices running Android 4.4 (API level 19) and lower don’t support downloading and installing split APKs, Google Play instead serves those devices a single APK, called a multi-APK, that’s optimized for the device’s configuration.

What are Dynamic Feature Modules?

Dynamic feature modules allow you to separate certain features and resources from the base module of your app and include them in your app bundle. Users can download and install these modules later on demand after they’ve already installed the base APK of the app using Dynamic Delivery. For example, if your app has a custom camera feature you can make it a dynamic module and users can download and install the custom camera on demand.

Creating a dynamic feature module

Dynamic feature modules are organized just like regular app modules. They provide their own code, resources, and assets in the directories you would expect. To add a dynamic feature module to your app project using Android Studio(3.2 Canary 14+), proceed as follows:

Note : Before creating a dynamic module, you have to create you app bundle .

1. Select File > New > New Module from the menu bar. In the Create New Module dialog, select Dynamic Feature Module and click Next.

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Android 11 storage FAQ

First introduced in Android 10, scoped storage is designed to protect app and user data and reduce file clutter. Since then, you’ve provided a lot of valuable feedback, which has helped us evolve the feature — thank you. Android 11 includes several notable enhancements that are based on your feedback. For example, we’ve enabled direct file path access to media files to improve compatibility of existing code and libraries. We understand that many apps, especially complex ones like Viber, require thoughtful planning to adopt scoped storage in order to continue supporting existing users, ensure adherence to current storage best practices, and maintain backward compatibility. Based on conversations with developers and lively discussions on public forums, we’ve prepared an FAQ to help you better understand various capabilities, behavior changes, and restrictions in scoped storage.

Does Scoped Storage allow apps to access files with file paths, using File API, for example?

• We recognize that some apps rely on code or libraries that access media file paths directly. Therefore on Android 11, apps with the read external storage permission are able to access files with file paths in the scoped storage environment. On Android 10 devices, this is not available to apps in the scoped storage environment unless they have opted-out by setting the android:requestLegacyExternalStorage manifest attribute. To ensure continuity across Android versions, if your app targets Android 10 or above, you should also opt-out. See scoped storage best practices for details.

How does the performance of file path access compare to Media Store APIs?

• The performance really depends on the exact use case. For sequential reads like in the case of playback of videos, file path access offers comparable performance to Media Store. However for random reads and writes, using file path can be up to twice as slow. For the fastest and most consistent read and writes we recommend Media Store APIs.

My app needs broad access to shared storage. Is Storage Access Framework the only option available?

• Storage Access Framework (SAF) is indeed one option that allows the user to grant access to directories and files. However, note that there are access restrictions to certain directories, such as the root and Android/data directories. While the majority of apps that need storage access can use best practices such as SAF or Media Store API, there could be cases where apps need broad access to shared storage or can’t do so efficiently with these best practices. For these cases, we have added the MANAGE_EXTERNAL_STORAGE permission to give access to all files on external storage, except the Android/data and Android/obb directories. To learn more about related Google Play guidelines, read the updated policy from the Policy Help Center.

What categories of apps should request the MANAGE_EXTERNAL_STORAGE permission?

• The MANAGE_EXTERNAL_STORAGE permission is intended for apps that have a core use case that requires broad access of files on a device, but cannot do so efficiently using scoped storage best practices. While it isn’t practical to enumerate all possible use cases, some use cases include file managers, backup and restore, anti-virus apps or productivity file editing apps.

Does using Storage Access Framework require Google Play policy approval?

• The Storage Access Framework has been in the platform since Android 4.4. Accessing files via Storage Access Framework gives users better control because the user is involved in picking files and it doesn’t require any user permissions. There’s no Google Play policy related to its usage.

Are there any further restrictions to using Storage Access Framework in Android 11 as compared to Android 10?

• Apps that target Android 11 (API level 30) and use Storage Access Framework will no longer be able to grant access to directories, such as the root directory of the SD card and the Download directory. Regardless of target SDK, Storage Access Framework on Android 11 cannot be used to gain access to Android/data and Android/obb directories. Learn more about these restrictions and ways to test the behaviors.

How can apps test out Scoped Storage changes?

• Apps can test out scoped storage behavior related to direct file path access or Media Store APIs via these compatibility flags. There’s also another compatibility flag to test the restrictions to access certain paths with Storage Access Framework.

Are apps in scoped storage limited to writing files into their app-specific data directories?

• In scoped storage, apps can contribute media files to Media Store collections. Media Store will put the files into well organized folders like DCIM, Movies, Download, and so on based on file type. For all such files, apps can also continue to have access via File APIs as well. The OS maintains a system to attribute an app to each media store file, so apps can read/write files that they originally contributed to the Media Store without needing storage permissions.

What is the guidance around using the Media Store DATA column since it’s been deprecated?

• On Android 10, apps in the scoped storage environment cannot access files using the file path. To be consistent with this design, we deprecated the DATA column then. Based on your feedback on the needs to work with existing native code or libraries, Android 11 now supports file path access for apps in scoped storage. Accordingly, the DATA column could actually be useful for some scenarios. For inserts and updates into the Media Store, apps in Scoped Storage should use DISPLAY_NAME and RELATIVE_PATH columns. They can no longer use the DATA column for this. When reading Media Store entries for files that exist on disk, the DATA column will have a valid file path, which can be used with the File API or NDK file libraries. Apps should however be prepared to handle any file I/O errors from these operations and should not assume the file is always available.

For apps that have opted out of Scoped Storage, when will they have to be compatible with Scoped Storage?

• On devices running Android 11 or higher, apps will be put into Scoped Storage as soon as they target Android 11 or higher.

What is the recommended way to migrate data that we currently store outside of Scoped Storage?

• preserveLegacyExternalStorage flag allows an app to retain legacy storage access on upgrades even while targeting Android 11. However beware that on new installs on Android 11, this flag has no effect. Please make code changes to adapt to Scoped Storage before targeting Android 11. Learn more about data migration best practices.

Are there any exceptions for Android/obb directories given that some package installers, like app stores, need access to it?

• Apps that hold the REQUEST_INSTALL_PACKAGES permission can access other apps’ Android/obb directories.

We hope you find this FAQ useful in planning your adoption of scoped storage. Please visit our best practice documentation for more information.

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Toolbar Android

• Toolbar is a view introduced in Android Lollipop(API 21) the spiritual successor of the ActionBar(Actionbar is replaced with Toolbar)
• Appearance and behavior can be more easily customized than the ActionBar.
• Works well with app’s targeted to API 21 and above.
• Android has updated the AppCompat support libraries so the Toolbar can be used on lower Android OS devices as well.

Toolbar Advantages

• Toolbar is a View included in a layout like any other View
• As a regular View, the toolbar is easier to position, animate and control

Using Toolbar as Action-Bar

• To use Toolbar as an ActionBar, first ensure the AppCompat-v7 support library is added to your application

build.gradle (Module:app) file

• disable the theme-provided ActionBar

• Now add a Toolbar to your Activity in layout file

• Activity.java

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Android App Development for beginners

This medium is for Android App developers for the beginners

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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.

At the end, please Subscribe to my newsletter DroidUp to get more tutorials and tips on Android development directly in your inbox.

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