How to Make a Variable in a build.gradle File and Pass It to a Kotlin File | Android Studio

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How to Make a Variable in a build.gradle File and Pass It to a Kotlin File | Android Studio | Kotlin

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How to Make a Variable in a build.gradle File and Pass It to a Kotlin File | Android Studio | Kotlin

last updated: 7 January 2024

In the build.gradle file, I wrote the funcCreateVariable function that creates a variable:

File build.gradle

...
android {

     defaultConfig {

          // my function for simple create variable
          def funcCreateVariable = {constantName, constantValue ->
               manifestPlaceholders += [ (constantName):constantValue]
               buildConfigField "String", "${constantName}", "\"${constantValue}\""
          }

          // my variables
          funcCreateVariable("MY_APPLICATION_LABEL", "Hello")
          funcCreateVariable("MY_APPLICATION_ICON", "@mipmap/ic_launcher")
     }

}

MY_APPLICATION_LABEL is my first variable in the build.gradle file
MY_APPLICATION_ICON is my second variable in the build.gradle file

In the AndroidManifest.xml file, to get the values from my variables, write like this: ${Variable name}

val text1 = BuildConfig.MY_APPLICATION_LABEL

Step 1. Creating a new project

Create a new simple project "Empty Views Activity" on Kotlin in Android Studio ...

Step 2. Let's change the code in the file build.gradle

File build.gradle

plugins {
     id 'com.android.application'
     id 'org.jetbrains.kotlin.android'
}

android {
     namespace 'com.example.androidkotlinapp1'
     compileSdk 33

     defaultConfig {
          applicationId "com.example.androidkotlinapp1"
          minSdk 27
          targetSdk 33
          versionCode 1
          versionName "1.0"

          testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"

          // my function for simple create variable
          def funcCreateVariable = {constantName, constantValue ->
               manifestPlaceholders += [ (constantName):constantValue]
               buildConfigField "String", "${constantName}", "\"${constantValue}\""
          }

          // my variables
          funcCreateVariable("MY_APPLICATION_LABEL", "Hello")
          funcCreateVariable("MY_APPLICATION_ICON", "@mipmap/ic_launcher")
     }

     buildTypes {
          release {
               minifyEnabled false
               proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
          }
     }
     compileOptions {
          sourceCompatibility JavaVersion.VERSION_1_8
          targetCompatibility JavaVersion.VERSION_1_8
     }
     kotlinOptions {
          jvmTarget = '1.8'
     }
}

dependencies {

     implementation 'androidx.core:core-ktx:1.7.0'
     implementation 'androidx.appcompat:appcompat:1.6.1'
     implementation 'com.google.android.material:material:1.9.0'
     implementation 'androidx.constraintlayout:constraintlayout:2.1.4'
     testImplementation 'junit:junit:4.13.2'
     androidTestImplementation 'androidx.test.ext:junit:1.1.5'
     androidTestImplementation 'androidx.test.espresso:espresso-core:3.5.1'
}

Step 3. Let's change the code in the file MainActivity.kt

The color indicates that a new code has been added.

File MainActivity.kt

package com.example.androidkotlinapp1

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle

class MainActivity : AppCompatActivity() {
     override fun onCreate(savedInstanceState: Bundle?) {
          super.onCreate(savedInstanceState)
          setContentView(R.layout.activity_main)

          val text1 = BuildConfig.MY_APPLICATION_LABEL
          // text1 = "Hello"
     }
}

Explanation:
The BuildConfig class is created itself when the project is compiled and is located in the build folder:

Note! Can I use my variables in the AndroidManifest.xml file?

In the AndroidManifest.xml file, to use the variable, you need to write like this: ${Variable name}

Let's take a look at the entire AndroidManifest.xml file:
The color indicates that a new code has been added.

File AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
     xmlns:tools="http://schemas.android.com/tools">

     <application
          android:allowBackup="true"
          android:dataExtractionRules="@xml/data_extraction_rules"
          android:fullBackupContent="@xml/backup_rules"
          android:icon="${MY_APPLICATION_ICON}"
          android:label="${MY_APPLICATION_LABEL}"
          android:supportsRtl="true"
          android:theme="@style/Theme.AndroidKotlinApp1"
          tools:targetApi="31">
          <activity
               android:name=".MainActivity"
               android:exported="true">
               <intent-filter>
                    <action android:name="android.intent.action.MAIN" />

                    <category android:name="android.intent.category.LAUNCHER" />
               </intent-filter>
          </activity>
     </application>

</manifest>

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