JNI开发第一个HellowWorld程序

 private  static native String  helloWorld();

//jni方法hellWorld对应的逻辑实现static jstring myhelloWorld(JNIEnv *env, jclass cls) {    return env->NewStringUTF("HelloWorld");}//static JNINativeMethod jniHelloWorl[] = {        {                "helloWorld",                "()Ljava/lang/String;",                (void *) myhelloWorld        }};

static bool registerNativeMethods(JNIEnv *env, const char *className, JNINativeMethod *jniMethods,                                  int methods) {    jclass clazz = env->FindClass(className);    if (clazz == NULL) {        return false;    }
    return env->RegisterNatives(clazz, jniMethods, methods) >= 0;}

//JNI_OnLoad里面完成jni方法的注册JNIEXPORT jint JNICALL JNI_OnLoad(JavaVM *vm, void *reserved) {

    int jniMethodSize = sizeof(JNINativeMethod);    JNIEnv *env = NULL;    if (vm->GetEnv((void **) &env, JNI_VERSION_1_6) != JNI_OK) {        return -1;    }    if (!registerNativeMethods(env, CLASS_NAME, jniHelloWorl, sizeof(jniHelloWorl) /                                                              jniMethodSize)) {        return -1;    }    LOGD("JNI Loaded");
    return JNI_VERSION_1_6;}

LOCAL_PATH := $(call my-dir)include $(CLEAR_VARS)LOCAL_MODULE := helloworldLOCAL_CFLAGS += -Wno-error=format-security -fpermissive -O2LOCAL_CFLAGS += -fno-rtti -fno-exceptionsLOCAL_CPPFLAGS += -std=c++11
LOCAL_SRC_FILES := HelloWorld.cpp
LOCAL_LDLIBS := -llog
include $(BUILD_SHARED_LIBRARY)

cmake_minimum_required(VERSION 3.4.1)project(helloworld)
add_definitions(-std=c++11)
set(${PROJECT_NAME}_SOURCES        HelloWorld.cpp        )
add_library(${PROJECT_NAME}        SHARED        ${${PROJECT_NAME}_SOURCES})
target_link_libraries(${PROJECT_NAME} log)

plugins {    id 'com.android.application'}
android {    compileSdkVersion 30    buildToolsVersion "30.0.2"
    defaultConfig {        applicationId "com.android.jnidemo01"        minSdkVersion 23        targetSdkVersion 30        versionCode 1        versionName "1.0"
        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
        externalNativeBuild {            //cmake编译方式参数配置            cmake {                arguments "-DCMAKE_BUILD_TYPE=Release  -DDEBUG=1"            }            //ndk编译参数配置            ndkBuild {                abiFilters 'armeabi-v7a', 'arm64-v8a'            }        }

    }
    buildTypes {        release {            minifyEnabled false            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'        }    }    compileOptions {        sourceCompatibility JavaVersion.VERSION_1_8        targetCompatibility JavaVersion.VERSION_1_8    }    //以下配置比较重要，cmake如果不注释就是使用cmake编译    //ndkBuild如果不注释就是使用ndk方式编译    externalNativeBuild {//        cmake {//            path file('src/main/cpp/CMakeLists.txt')//        }        ndkBuild {            path file("src/main/cpp/Android.mk")        }    }}
dependencies {
    implementation 'androidx.appcompat:appcompat:1.2.0'    implementation 'com.google.android.material:material:1.2.1'    implementation 'androidx.constraintlayout:constraintlayout:2.0.4'    testImplementation 'junit:junit:4.+'    androidTestImplementation 'androidx.test.ext:junit:1.1.2'    androidTestImplementation 'androidx.test.espresso:espresso-core:3.3.0'}

static {    System.loadLibrary("helloworld");}