Android JNI ndk-build error: 'jni' has not been declared

Question

I want to use dynamic registration in native method, so I need set JNI_onLoad function. I just write a function to get sum of two numbers. But, it can't build correctly. How can I correct the error?

• This is my *.cpp file, I name this file jni.cpp

  #include <jni.h>
  extern "C" JNIEXPORT jint JNI_OnLoad(JavaVM *vm, void *reserved) {
  
      jni::JNIEnv& env = jni::GetEnv(*vm, jni::jni_version_1_6);
      jni::jclass& nativeClass = jni::FindClass(env, "com/test/NativeClass");
  
      #define MAKE_NATIVE_METHOD(name, sig) jni::MakeNativeMethod<decltype(name), name>( #name, sig )
      jni::RegisterNatives(env, nativeClass, MAKE_NATIVE_METHOD(nativeAddTest, "(II)I")        );
  
      return JNI_VERSION_1_6;
   }
  
  jlong nativeAddTest(JNIEnv *env, jni::jobject* obj, jni::jint a, jni::jint b) {
      return a+b;
  }
  

• Android.mk

   LOCAL_PATH := $(call my-dir)
  
   include $(CLEAR_VARS)
  
   LOCAL_MODULE    := test
   LOCAL_SRC_FILES := jni.cpp
   LOCAL_LDLIBS := -L/ndk-path/sources/cxx-stl/stlport/libs/armeabi
  
   include $(BUILD_SHARED_LIBRARY)
  

• When I use ndk-build command, it's wrong. But I really dont't konw the reason...

  D:\WorkSpaces\Test\app\src\main\jni>ndk-build
    [x86] Compile++      : test <= jni.cpp
  D:/WorkSpaces/Test/app/src/main/jni/jni.cpp: In function 'jint JNI_OnLoad(JavaVM*, void*)':
  D:/WorkSpaces/Test/app/src/main/jni/jni.cpp:9:5: error: 'jni' has not been declared
     jni::JNIEnv& env = jni::GetEnv(*vm, jni::jni_version_1_6);
     ^
  D:/WorkSpaces/Test/app/src/main/jni/jni.cpp:9:18: error: 'env' was not declared in this scope
     jni::JNIEnv& env = jni::GetEnv(*vm, jni::jni_version_1_6);
  ....
  

It seems can't find jni.h, but I already have #include<jni.h>

Answer 1

In Android NDK, <jni.h> does not define a jni namespace. Simply remove all jni::

#include <jni.h>
extern "C" JNIEXPORT jint JNI_OnLoad(JavaVM *vm, void *reserved) {

   JNIEnv env;
   vm->GetEnv(reinterpret_cast<void**>(&env), JNI_VERSION_1_6);
   jclass nativeClass = env->FindClass("com/test/NativeClass");

… and so on.

Answer 2

Add header location to your android.mk

LOCAL_C_INCLUDES := "path to your header location"