Dedup the gradle bits of audio-echo.

audio-echo/app/build.gradle

@@ -1,20 +1,10 @@
 plugins {
-    id 'com.android.application'
+    id "ndksamples.android.application"
 }
 
 android {
-    compileSdk 33
-    ndkVersion '25.1.8937393'
-
     defaultConfig {
         applicationId 'com.google.sample.echo'
-        /*
-           To run on earlier version of Android than android-21, do:
-             *) set this minSDKVersion and cmake's ANDROID_PLATFORM to your version
-             *) set ANDROID_STL to c++_static for some very earlier version android.
-         */
-        minSdkVersion 23
-        targetSdkVersion 33
         versionCode 1
         versionName '1.0'
         externalNativeBuild {
@@ -23,13 +13,6 @@ android {
             }
         }
     }
-    buildTypes {
-        release {
-            minifyEnabled false
-            proguardFiles getDefaultProguardFile('proguard-android.txt'),
-                          'proguard-rules.pro'
-        }
-    }
     externalNativeBuild {
         cmake {
             path 'src/main/cpp/CMakeLists.txt'
@@ -39,6 +22,5 @@ android {
 }
 
 dependencies {
-    implementation fileTree(dir: 'libs', include: ['*.jar'])
-    implementation 'androidx.appcompat:appcompat:1.5.1'
+    implementation libs.appcompat
 }

build-logic/README.md

@@ -0,0 +1,11 @@
+# Convention plugins
+
+This directory contains [convention plugins] used by the NDK samples. These are
+used to remove Gradle boiler plate from individual samples in favor of common
+configuration here. Using convention plugins for single module projects is
+overkill, but any non-trivial app will likely need their own eventually. See
+[Now In Android's build-logic][nia-build-logic] for a more thorough example of
+building convention plugins for Android projects.
+
+[convention plugins]: https://docs.gradle.org/current/samples/sample_convention_plugins.html
+[nia-build-logic]: https://github.com/android/nowinandroid/blob/main/build-logic/README.md

build-logic/build.gradle.kts

@@ -0,0 +1,31 @@
+import org.jetbrains.kotlin.gradle.tasks.KotlinCompile
+
+plugins {
+    id("java-gradle-plugin")
+    `kotlin-dsl`
+    alias(libs.plugins.jetbrains.kotlin.jvm)
+}
+
+java {
+    sourceCompatibility = JavaVersion.VERSION_17
+    targetCompatibility = JavaVersion.VERSION_17
+}
+
+tasks.withType<KotlinCompile>().configureEach {
+    kotlinOptions {
+        jvmTarget = JavaVersion.VERSION_17.toString()
+    }
+}
+
+dependencies {
+    compileOnly(libs.android.gradlePlugin)
+}
+
+gradlePlugin {
+    plugins {
+        register("androidApplication") {
+            id = "ndksamples.android.application"
+            implementationClass = "com.android.ndk.samples.buildlogic.AndroidApplicationConventionPlugin"
+        }
+    }
+}

build-logic/settings.gradle.kts

@@ -0,0 +1,13 @@
+dependencyResolutionManagement {
+    repositories {
+        google()
+        mavenCentral()
+    }
+    versionCatalogs {
+        create("libs") {
+            from(files("../gradle/libs.versions.toml"))
+        }
+    }
+}
+
+rootProject.name = "build-logic"

build-logic/src/main/java/com/android/ndk/samples/buildlogic/AndroidApplicationConventionPlugin.kt

@@ -0,0 +1,26 @@
+package com.android.ndk.samples.buildlogic
+
+import com.android.build.api.dsl.ApplicationExtension
+
+import org.gradle.api.Plugin
+import org.gradle.api.Project
+import org.gradle.kotlin.dsl.configure
+
+class AndroidApplicationConventionPlugin : Plugin<Project> {
+    override fun apply(target: Project) {
+        with(target) {
+            with(pluginManager) {
+                apply("com.android.application")
+            }
+
+            extensions.configure<ApplicationExtension> {
+                compileSdk = Versions.COMPILE_SDK
+                ndkVersion = Versions.NDK
+                defaultConfig {
+                    minSdk = Versions.MIN_SDK
+                    targetSdk = Versions.TARGET_SDK
+                }
+            }
+        }
+    }
+}

build-logic/src/main/java/com/android/ndk/samples/buildlogic/Versions.kt

@@ -0,0 +1,8 @@
+package com.android.ndk.samples.buildlogic
+
+object Versions {
+    const val COMPILE_SDK = 34
+    const val TARGET_SDK = 34
+    const val MIN_SDK = 21
+    const val NDK = "26.3.11579264" // r26d
+}

gradle/libs.versions.toml

@@ -6,6 +6,7 @@ junitVersion = "1.1.5"
 espressoCore = "3.5.1"
 appcompat = "1.6.1"
 material = "1.12.0"
+jetbrainsKotlinJvm = "1.7.21"
 
 [libraries]
 junit = { group = "junit", name = "junit", version.ref = "junit" }
@@ -14,7 +15,11 @@ espresso-core = { group = "androidx.test.espresso", name = "espresso-core", vers
 appcompat = { group = "androidx.appcompat", name = "appcompat", version.ref = "appcompat" }
 material = { group = "com.google.android.material", name = "material", version.ref = "material" }
 
+# build-logic dependencies
+android-gradlePlugin = { group = "com.android.tools.build", name = "gradle", version.ref = "agp" }
+
 [plugins]
 android-application = { id = "com.android.application", version.ref = "agp" }
 android-library = { id = "com.android.library", version.ref = "agp" }
 jetbrainsKotlinAndroid = { id = "org.jetbrains.kotlin.android", version.ref = "kotlin" }
+jetbrains-kotlin-jvm = { id = "org.jetbrains.kotlin.jvm", version.ref = "jetbrainsKotlinJvm" }

settings.gradle

@@ -1,4 +1,5 @@
 pluginManagement {
+    includeBuild("build-logic")
     repositories {
         google {
             content {