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

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!
    ...

There are a couple of things that can lead to "no implementation found". One is getting the function prototype name wrong, another is failing to load the .so at all. Are you sure that System.loadLibrary() is being called before the method is used?

If you don't have a JNI_OnLoad function defined, you may want to create one and have it spit out a log message just to verify that the lib is getting pulled in successfully.

You already dodged the most common problem -- forgetting to use extern "C" -- so it's either the above or some slight misspelling. What does the Java declaration look like?