Android_NDK_c调用java代码

1.找到class字节码文件

jclass clazz = (*env)->FindClass(env, "com/example/ndk/MainActivity");
if(clazz == 0){ //如果该字节码文件不存在
LOGI("error clazz");
return;
}

2.找到Method方法

jmethodID method = (*env)->GetMethodID(env, clazz, "add","(II)I");
if(method == 0){
LOGI("method error");
return;
}

3.调用相应的方法

jint result = (*env)->CallIntMethod(env,obj,method,4, 10);//第二个为操作的对象，method为调用的方法，后面为参数信息
LOGI("result = %d", result);

/*jstring barr = (jstring)(*env)->CallObjectMethod(env,obj,method);	//可以执行强转
char* charss = Jstring2CStr(env, barr);*/

4.补:将jstring转为char*

//将java语言的就string 转化为c语言中的*char类型
char* Jstring2CStr(JNIEnv* env, jstring jstr) {
char* rtn = NULL;
jclass clsstring = (*env)->FindClass(env, "java/lang/String");
jstring strencode = (*env)->NewStringUTF(env, "utf-8");
jmethodID mid = (*env)->GetMethodID(env, clsstring, "getBytes",
"(Ljava/lang/String;)[B");
jbyteArray barr = (jbyteArray)(*env)->CallObjectMethod(env, jstr, mid,
strencode); // String .getByte("GB2312");
jsize alen = (*env)->GetArrayLength(env, barr);
jbyte* ba = (*env)->GetByteArrayElements(env, barr, JNI_FALSE);
if (alen > 0) {
rtn = (char*) malloc(alen + 1); //"\0"
memcpy(rtn, ba, alen);
rtn[alen] = 0;
}
(*env)->ReleaseByteArrayElements(env, barr, ba, 0); //
return rtn;
}