No implementation found for native code in android

Question

Now Im using ffmpeg java library in android. I want to use it directly in my app, So Im inporting this library. But I have a problem with it.

E/AndroidRuntime: FATAL EXCEPTION: main
              Process: com.softcode.kihnoplay, PID: 15313
              java.lang.UnsatisfiedLinkError: No implementation found for java.lang.String androidFfmpeg.ArmArchHelper.cpuArchFromJNI() (tried Java_androidFfmpeg_ArmArchHelper_cpuArchFromJNI and Java_androidFfmpeg_ArmArchHelper_cpuArchFromJNI__)
                  at androidFfmpeg.ArmArchHelper.cpuArchFromJNI(Native Method)
                  at androidFfmpeg.CpuArchHelper.getCpuArch(CpuArchHelper.java:16)
                  at androidFfmpeg.FFmpeg.loadBinary(FFmpeg.java:40)
                  at com.softcode.tablet.Mp3Concat_Thread.startThread(Mp3Concat_Thread.java:90)
                  at com.softcode.tablet.Mp3Concat_Thread.<init>(Mp3Concat_Thread.java:54)
                  at com.softcode.phone.record.view.RecordActivity.onCreate(RecordActivity.java:182)
                  at android.app.Activity.performCreate(Activity.java:6955)
                  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1126)
                  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2927)
                  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3045)
                  at android.app.ActivityThread.-wrap14(ActivityThread.java)
                  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1642)
                  at android.os.Handler.dispatchMessage(Handler.java:102)
                  at android.os.Looper.loop(Looper.java:154)
                  at android.app.ActivityThread.main(ActivityThread.java:6776)
                  at java.lang.reflect.Method.invoke(Native Method)
                  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1520)
                  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1410)

I don't know why this error is occurring.

My directory tree is

and c file code.

#include <jni.h>
#include <stdio.h>
#include <stdlib.h>
#include <cpu-features.h>

jstring
Java_androidFfmpeg_ArmArchHelper_cpuArchFromJNI(JNIEnv* env, jobject       obj)
{
char arch_info[11] = "";

if (android_getCpuFamily() == ANDROID_CPU_FAMILY_ARM) {
    strcpy(arch_info, "ARM");

    uint64_t cpuFeatures = android_getCpuFeatures();
    if ((cpuFeatures & ANDROID_CPU_ARM_FEATURE_ARMv7) != 0) {
        strcat(arch_info, " v7");

        if((cpuFeatures & ANDROID_CPU_ARM_FEATURE_NEON) != 0) {
            strcat(arch_info, "-neon");
        }
    }
}
return (*env)->NewStringUTF(env, arch_info);
}

And this is a grade(app)

android {
compileSdkVersion 27
buildToolsVersion '27.0.3'
defaultConfig {
    applicationId "com.softcode.kihnoplay"
    minSdkVersion 21
    targetSdkVersion 25
    versionCode 1
    versionName "1.00"
    testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"

    renderscriptTargetApi 19
    renderscriptSupportModeEnabled true

    ndk {
        abiFilters "armeabi", "armeabi-v7a","x86"
    }

    aaptOptions
            {
                cruncherEnabled = false
            }
}

buildTypes {
    debug {
        minifyEnabled false
        proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
    }
    release {
        minifyEnabled false
        proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
    }
}
sourceSets.main {
    jniLibs.srcDir 'src/main/libs'
    jni.srcDirs = [] //important!!!! disable automatic ndk-build call
}

I don't know why this error is occurring. If you know this problem please let me know. Thanks you!

Answer 1

I guess you are using a clang++ compiling c source code, right? If true, try to change your file name to be armArch.cpp and add keyword extern into your C header and source files. e.g.

#ifdef __cplusplus
extern "C" {
#endif

// your function declarations or implementations. 

#ifdef __cplusplus
}
#endif

Also, i would like to suggest use externalNativeBuild and cmake block rather than the older ndk block which is not the modern convention for Android native builds. E.g.

android {

    //....

    defaultConfig {
        applicationId "com.softcode.kihnoplay"
        minSdkVersion 21
        targetSdkVersion 25
        versionCode 1
        versionName "1.00"
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"

        externalNativeBuild {
            cmake {
                cppFlags "-std=c++11 -frtti -fexceptions"
                abiFilters 'armeabi-v7a', 'arm64-v8a', 'x86', 'x86_64' 
            }
        }
    }
    buildTypes {
        release {
            //....
        }
    }

    externalNativeBuild {
        cmake {
            path "CMakeLists.txt"
        }
    }
}

Android NDK has deprecated armeabi, you don't actually need to include this ABI is your abiFilters setting. ABIs 'armeabi-v7a', 'arm64-v8a', 'x86', 'x86_64' will be enough for supporting almost all the current Android devices as well as emulators.

You can find a comprehensive JNI tutorial from https://arophix.com/2017/12/17/andoid-jni-summary/ and a sample JNI project from https://github.com/russell-shizhen/JniExample