[NDK开发]Android JNI开发之动态注册

package com.biumall.mydynamic2;
public class MyDynamic {
    static {
        System.loadLibrary("MyDynamic");
    }
    /***
     *   1. javac MyDynamic2.java
     *   2. javap -s MyDynamic2.class
     *
     *  public static native java.lang.String StringFormJNI();
     *     Signature: ()Ljava/lang/String;
     *
     *   public static native void StringToJNI(java.lang.String);
     *     Signature: (Ljava/lang/String;)V
     *
     */
    public static native String StringFormJNI();
    public static native void StringToJNI(String message);
}

public class MainActivity extends AppCompatActivity {
    String TAG= "Dynamic_Android_Log";
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Log.d(TAG, "onCreate  : "+ MyDynamic.StringFormJNI());
        MyDynamic.StringToJNI("Hello from Android.");
    }
}

#include<string.h>
#include<jni.h>
#include<stdio.h>
#include <android/log.h>
#define LOG_TAG "Dynamic_JNI_Log"
#define LOGD(...) __android_log_print(ANDROID_LOG_DEBUG, LOG_TAG, __VA_ARGS__)
#define LOGI(...) __android_log_print(ANDROID_LOG_INFO, LOG_TAG, __VA_ARGS__)
#define LOGE(...) __android_log_print(ANDROID_LOG_ERROR, LOG_TAG, __VA_ARGS__)
//获取数组大小
#define ARRAY_LENGTH(x) ((int)(sizeof(x) / sizeof((x)[0])))
//定义MyDynamic.java类目录(就是包名+类名，只不过.换成了/)
#define DYNAMIC_CLASS "com/biumall/mydynamic2/MyDynamic"
// 定义native 实现的StringFormJNI
JNIEXPORT jstring JNICALL native_StringFormJNI(JNIEnv *env , jclass clasz) {
    LOGD("--------native_StringFormJNI----------");
    return (*env)->NewStringUTF(env, "Hello form JNI.");
}
// 定义native 实现的StringToJNI
JNIEXPORT void JNICALL native_StringToJNI(JNIEnv *env, jclass clasz, jstring message){
     LOGD("native_StringToJNI===%s",(*env)->GetStringUTFChars(env, message, 0));
}
//定义Java和JNI函数的绑定表
// 方法数组，分别为：
// 方法名 | 方法签名 | 函数指针
// 可以通过javac和javap 获取 方法签名
JNINativeMethod method_table[]= {
 {"StringFormJNI", "()Ljava/lang/String;", (void*) native_StringFormJNI},
 {"StringToJNI", "(Ljava/lang/String;)V", (void *) native_StringToJNI},
};
int registerNativeMethods(JNIEnv *env, const char *className, JNINativeMethod * methods, int methods_size){
    jclass clazz = NULL;
    //反射Java类
    clazz = (*env)->FindClass(env, className);
    if(NULL == clazz){
        return JNI_ERR;
    }
    int result = (*env)->RegisterNatives(env, clazz, methods, methods_size);
    LOGD("--------registerNativeMethods---------- result : %d", result);
    if(result < 0){
        return JNI_ERR;
    }
    return JNI_OK;
}
JNIEXPORT jint JNI_OnLoad(JavaVM *vm, void *reserved){
    JNIEnv * env = NULL;
    int result = (*vm)->GetEnv(vm, (void **) &env, JNI_VERSION_1_6);
    LOGD("--------JNI_OnLoad----------1 result : %d", result);
    if(result != JNI_OK){
        return JNI_ERR;
    }
    result = registerNativeMethods(env , DYNAMIC_CLASS, method_table, ARRAY_LENGTH(method_table));
    LOGD("--------JNI_OnLoad----------2 result : %d", result);
    if(result != JNI_OK){
        return JNI_ERR;
    }
    return JNI_VERSION_1_6;
}

LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_LDLIBS := -llog
LOCAL_MODULE    := MyDynamic
LOCAL_SRC_FILES := MyDynamic.c
include $(BUILD_SHARED_LIBRARY)

APP_ABI := all

android {
    compileSdkVersion 31
    // 略
    sourceSets {
        main {
            jniLibs.srcDirs = ['libs']
        }
    }
}