1. 靜態註冊

jni開發中預設註冊方式為靜態註冊，具體如下：

// MainActivity.java
public class MainActivity extends AppCompatActivity {

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

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        TextView tv 
 
= findViewById(R.id.sample_text);
        tv.setText(stringFromJNI());
    }
    public native String stringFromJNI();

}

// native-lib.cpp
extern "C" JNIEXPORT jstring JNICALL
Java_com_example_myndkproject_MainActivity_stringFromJNI(
        JNIEnv* env,
        jobject /* this */) {
    std::string hello = "
 
Hello from C++ 靜態註冊";
    return env->NewStringUTF(hello.c_str());
}

在java中通過native stringFromJNI()呼叫Java_com_example_myndkproject_MainActivity_stringFromJNI，達到使用C++程式碼開發核心內容的目的。

2. 動態註冊

// MainActivity.java

public class MainActivity extends AppCompatActivity {
    static {
        System.loadLibrary("native-lib");
    }
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        TextView tv = findViewById(R.id.sample_text);
        tv.setText(stringFromJNI());
        Log.i("MainActivity",add_java(1,2)+"");
    }
    public native String stringFromJNI();
    public native int add_java(int a,int b);

}

// native-lib.cpp
jstring stringFromJNI(JNIEnv *env, jobject thiz){
    std::string hello = "Hello from C++ 動態註冊";
    return env->NewStringUTF(hello.c_str());
}

jint add_jni(JNIEnv *env,jobject thiz,jint a, jint b )
{
    return a+b;
}

static const JNINativeMethod gMethods[] = {
        {"stringFromJNI", "()Ljava/lang/String;", (jstring*)stringFromJNI},
        {"add_java","(II)I",(jint*)add_jni},

};

JNIEXPORT jint JNI_OnLoad(JavaVM* vm, void* reserved){

    __android_log_print(ANDROID_LOG_INFO, "native", "Jni_OnLoad");
    JNIEnv* env = NULL;
    if(vm->GetEnv((void**)&env, JNI_VERSION_1_4) != JNI_OK) //從JavaVM獲取JNIEnv，一般使用1.4的版本
        return -1;
    jclass clazz = env->FindClass("com/example/myndkproject/MainActivity");
    if (!clazz){
        __android_log_print(ANDROID_LOG_INFO, "native", "cannot get class: com/example/myndkproject/MainActivity");
        return -1;
    }
    if(env->RegisterNatives(clazz, gMethods, sizeof(gMethods)/sizeof(gMethods[0])))
    {
        __android_log_print(ANDROID_LOG_INFO, "native", "register native method failed!\n");
        return -1;
    }
    return JNI_VERSION_1_4;
}