程式語言 - Java - Android - NDK - Hello, world!

編譯環境

$ java -version
    openjdk version "17.0.17" 2025-10-21

$ sdkmanager --version
    12.0

$ gradle --version
    Gradle 8.2

$ sdkmanager "platform-tools" "platforms;android-34" "build-tools;34.0.0"

settings.gradle

pluginManagement {
    repositories {
        google()
        mavenCentral()
        gradlePluginPortal()
    }
}
dependencyResolutionManagement {
    repositories {
        google()
        mavenCentral()
    }
}
rootProject.name = "hello-android"
include(":app")

build.gradle

buildscript {
    repositories {
        google()
        mavenCentral()
    }
    dependencies {
        classpath "com.android.tools.build:gradle:8.2.2"
    }
}

執行如下命令：

$ gradle wrapper
$ ./gradlew
$ mkdir -p app/src/main/cpp
$ mkdir -p app/src/main/java/com/example/hello
$ mkdir -p app/src/main/res

app/build.gradle

plugins {
    id 'com.android.application'
}

android {
    namespace 'com.example.hello'
    compileSdk 34

    defaultConfig {
        applicationId "com.example.hello"
        minSdk 21
        targetSdk 34
        versionCode 1
        versionName "1.0"

        externalNativeBuild {
            cmake {
                cppFlags "-std=c++17"
            }
        }
    }

    buildTypes {
        release {
            minifyEnabled false
        }
    }

    externalNativeBuild {
        cmake {
            path "src/main/cpp/CMakeLists.txt"
        }
    }

    ndkVersion "27.0.12077973"
}

app/src/main/AndroidManifest.xml

<manifest xmlns:android="http://schemas.android.com/apk/res/android">
    <application
        android:label="HelloApp">
        <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>

app/src/main/java/com/example/hello/MainActivity.java

package com.example.hello;

import android.app.Activity;
import android.os.Bundle;
import android.widget.TextView;

public class MainActivity extends Activity {

    static {
        System.loadLibrary("native-lib");
    }

    private native String stringFromJNI();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        TextView tv = new TextView(this);
        tv.setText(stringFromJNI());
        tv.setTextSize(24);
        setContentView(tv);
    }
}

app/src/main/cpp/CMakeLists.txt

cmake_minimum_required(VERSION 3.22.1)

project("myndkapp")

add_library(
    native-lib
    SHARED
    native-lib.cpp
)

find_library(
    log-lib
    log
)

target_link_libraries(
    native-lib
    ${log-lib}
)

app/src/main/cpp/native-lib.cpp

#include <jni.h>
#include <string>

extern "C" JNIEXPORT jstring JNICALL
Java_com_example_hello_MainActivity_stringFromJNI(JNIEnv* env, jobject _this) {
    std::string hello = "Hello from C++";
    return env->NewStringUTF(hello.c_str());
}

編譯

$ ./gradlew assembleDebug
$ file app/build/outputs/apk/debug/app-debug.apk
    app/build/outputs/apk/debug/app-debug.apk: Android package (APK), with gradle app-metadata.properties, with APK Signing Block

完成