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When developing an Android application, we can generate an AAR file and use it in different android projects. 

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Creating an Android Library will save you time compiling and running your project, and you can share existing services, images, resources, layouts with other people.

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## ***Libraries make reusing existing code very convenient.***

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As you build your library, remember this quote:

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“*If you wish to make an apple pie from scratch, you must first invent the universe*.” ― Carl Sagan, Cosmos

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So let’s get started.

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## **Creating an Android Library**

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Starting process: 

## **Project Setup → Open a new project → Select an Empty Project Template**

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This would create an empty Android project.

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Click **File > New > New Module**.

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In the **Create New Module** window that appears, click **Android Library**

 ![](https://cdn.hackernoon.com/images/-4d139vp.png)

Then give your library a name and select a minimum SDK version for the code in the library, then click **Finish**.

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The library module appears in the Project panel on the left.

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At the top of the file, you should include the following line if it is not already there.

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```javascript
apply plugin: 'com.android.library'
```

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`~/woah/build.gradle`

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```java
plugins {
    id 'org.jetbrains.kotlin.android'
    id 'com.android.library'
}

android {
    compileSdk 31

    compileOptions {
        targetCompatibility JavaVersion.VERSION_1_8
    }

    buildTypes {
        release {
            minifyEnabled true
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    implementation 'androidx.core:core-ktx:1.7.0'
}
```

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Try to simply **Build > Rebuild project** or execute in terminal:

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```javascript
./gradlew assembleRelease 
```

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or **choose** `assembleRelease` **from Android Studio's Gradle menu**.

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After a successful build, First switch to the project view in the left panel and navigate as sown below.

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AAR file should appear in `~/woah/build/outputs/aar/`

 ![](https://cdn.hackernoon.com/images/-sd239fq.png)

AAR files can contain Android resources and a manifest file, which allows you to bundle in shared resources like layouts and drawables in addition to Java classes and methods.

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AAR files can contain C/C++ libraries for use by the app module's C/C++ code.

## **Implement Your logic in your Library Module**

Let’s write a simple library that is shown when your app gets crashed.

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```java
interface CrashListener {
    fun onUncaughtException(thread: Thread, throwable: Throwable)
}

object Woah {
    @JvmStatic
    fun init(crashListener: CrashListener) {
        Thread.setDefaultUncaughtExceptionHandler { p0, p1 ->
             crashListener.onUncaughtException(p0, p1)
        }
    }
}
```

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Adding @Keep on a class protects the class from removing by proguard during optimization.

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Don’t use default resource names such as `colorAccent` or `colorPrimary` in resources.

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Default host app resources will always be prioritized.

## **How to Integrate AAR Library**

Just move the AAR file to the libs directory.

 ![](https://cdn.hackernoon.com/images/-pma3ihb.png)

Then add in `build.gradle` file:

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```javascript
dependencies {
    implementation project(':woah')
    implementation fileTree(dir: "libs", include: ["*.aar"])
    ...
}
```

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# **Conclusion**

In this guide, we have covered all the steps you need to take to create an Android Library.

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The goal of creating an Android Library should be to develop more user-friendly interfaces that can be reused.

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## **Resources:**

**Sample (full code)**

<https://github.com/tkrest/woah>

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**Android-library**

<https://developer.android.com/studio/projects/android-library>

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**Dependencies**

[https://developer.android.com/studio/build/dependencies](https://developer.android.com/studio/build/dependencies?buildsystem=ndk-build)

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\


Cosmos

Apple

2022 - Android Advocate of the Year

2022 - HackerNoon Contributor of the Year - Firebase

2022 - HackerNoon Contributor of the Year - Kotlin

2022 - HackerNoon Contributor of the Year - Performance

Nominated for 2022 - Android Advocate of the Year

Nominated for 2022 - HackerNoon Contributor of the Year - Performance

Nominated for 2022 - HackerNoon Contributor of the Year - Firebase

Nominated for 2022 - HackerNoon Contributor of the Year - Kotlin

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How to Create an Android Library

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