Android NDK C++ JNI (no implementation found for native…)

Question

I\'m trying to use the NDK with C++ and can\'t seem to get the method naming convention correct. my native method is as follows:

extern \"C\" {
JNIEXPORT voi         


        

Answer 1

If your package name includes _ character, you should write 1(one) after _ character as shown below:

MainActivity.java

package com.example.testcpp_2;

native-lib.cpp

JNICALL
Java_com_example_testcpp_12_MainActivity_stringFromJNI(

Answer 2

An additional reason: Use LOCAL_WHOLE_STATIC_LIBRARIES instead of LOCAL_STATIC_LIBRARIES in android.mk. This stops the library from optimizing out unused API calls because the NDK cannot detect the use of the native bindings from java code.

Answer 3

I Faced the same problem, and in my case the reason was that I had underscore in package name "RFID_Test" I renamed the Package and it worked. Thanks user1222021

Answer 4

I had the same problem, but to me the error was in the file Android.mk. I had it:

LOCAL_SRC_FILES := A.cpp
LOCAL_SRC_FILES := B.cpp 

but should have this:

LOCAL_SRC_FILES := A.cpp
LOCAL_SRC_FILES += B.cpp 

note the detail += instead :=

I hope that helps.

Answer 5

There is a cpp example under apps in ndk: https://github.com/android/ndk-samples/blob/master/hello-gl2/app/src/main/cpp/gl_code.cpp

Answer 6

An additional cause for this error: your undecorated native method name must not contain an underscore!

For example, I wanted to export a C function named AudioCapture_Ping(). Here is my export declaration in C:

JNI_EXPORT int Java_com_obsidian_mobilehashhost_MainActivity_AudioCapture_Ping(JNIEnv *pJniEnv, jobject object);  //Notice the underscore before Ping

Here was my Java class importing the function:

package com.obsidian.mobileaudiohashhost;
...
public class MainActivity extends Activity {
    private native int AudioCapture_Ping();  // FAILS
    ...

I could not get Android to dynamically link to my native method until I removed the underscore:

JNI_EXPORT int Java_com_obsidian_mobilehashhost_MainActivity_AudioCapturePing(JNIEnv *pJniEnv, jobject object); 

package com.obsidian.mobileaudiohashhost;
...
public class MainActivity extends Activity {
    private native int AudioCapturePing();  // THIS WORKS!
    ...