Kamal Sharma Kamal Sharma - 1 year ago 185
Android Question

ndk build and .so file creation android

i am new in android ndk.

I am working on a app which needs java code as well c/c++ code

So, for that i need android ndk.

But i stuck at this point that i cannot run ndk-build which makes the connection between java and c/c++.

So. please someone help me out to solve this problem.

I tried on both windows and linux but got same error.

I got this error when i use ndk-build .

/home/kamal/android-ndk-r8e/build/core/add-application.mk:128: Android NDK:
Compile thumb : ndk <= native.c
jni/native.c: In function 'Java_com_example_demo_MainActivity_hello':
jni/native.c:4:3: error: parameter name omitted
jni/native.c:4:3: error: parameter name omitted
jni/native.c:5:10: error: 'env' undeclared (first use in this function)
jni/native.c:5:10: note: each undeclared identifier is reported only once for each function it appears in
jni/native.c: In function 'Java_com_example_demo_MainActivity_add':
jni/native.c:9:3: error: parameter name omitted
jni/native.c:9:3: error: parameter name omitted
jni/native.c:9:3: error: parameter name omitted
jni/native.c:9:3: error: parameter name omitted
jni/native.c:10:9: error: 'value1' undeclared (first use in this function)
jni/native.c:10:18: error: 'value2' undeclared (first use in this function)
make: *** [obj/local/armeabi/objs/myjni/native.o] Error 1

Answer Source

First of all you are getting this error because you are not declaring parameter in is must to create conection between java and c/c++.

SO, i am sending you my code for your problem

1.First of all create android project in eclipse.

  1. create folder under project click -> click new -> then folder and name it jni.

  2. create one more folder under jni nameing include.

  3. create java class.

  4. code for java class nameing-(MainActivity.java)->

     package com.example.ndk;
    import android.os.Bundle;
    import android.app.Activity;
    import android.view.Menu;
     public class MainActivity extends Activity {
     static {
    * Adds two integers, returning their sum
    public native int add( int v1, int v2 );
    * Returns Hello World string
    public native String hello();
    public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
  5. open command prompt or press window+R.

  6. move to directory- (workspace-> project name -> jni -> include).

  7. run command under this directory.

        javah -classpath <project-name>/bin/classes;<ANDROID_SDK_HOME>\platforms\android-<xx>\android.jar -o HelloJNI.h com.example.test.MainActivity
  8. after this we can see "HelloJNI.h" file under include folder.

  9. check "HelloJNI.h" have this lines in it

    JNIEXPORT jint JNICALL Java_com_example_ndk_MainActivity_add(JNIEnv *, jobject, jint, jint);
    JNIEXPORT jstring JNICALL Java_com_example_ndk_MainActivity_hello (JNIEnv *, jobject);
  10. create new file under jni naming test.c (use this 2 points in pont 10 in this file test.c)

       #include <jni.h>
       #include "include/HelloJNI.h"
    JNIEXPORT jstring JNICALL Java_com_example_ndk_MainActivity_hello
        (JNIEnv *env, jobject javaThis) {
        return (*env)->NewStringUTF(env, "Hello");
      JNIEXPORT jint JNICALL Java_com_example_ndk_MainActivity_add
          (JNIEnv *env, jobject javaThis, jint value1, jint value2){
    return (value1 + value2);
  11. create new file under jni naming Android.mk

    LOCAL_PATH := $(call my-dir)
    include $(CLEAR_VARS)
    LOCAL_MODULE    := myjni       // from point 5 
     LOCAL_SRC_FILES := test.c     //from point 10 that we creare test.c
     include $(BUILD_SHARED_LIBRARY)
  12. create new file NDKActivity.java

      package com.example.ndk;
      import android.app.Activity;
      import android.view.View.OnClickListener;
      import android.os.Bundle;
      import android.view.View;
      import android.widget.Button;
      import android.widget.EditText;
      import android.widget.TextView;
      public class NDKActivity extends Activity{
      Button buttonCalc;
      TextView result;
      EditText value1,value2;
      /** Called when the activity is first created. */
      MainActivity nativeLib;
      public void onCreate(Bundle savedInstanceState) {
     nativeLib = new MainActivity();
      String helloText = nativeLib.hello();
    result = (TextView) findViewById(R.id.result);
    value1 = (EditText) findViewById(R.id.value1);
    value2 = (EditText) findViewById(R.id.value2);
    // Update the UI
    TextView outText = (TextView) findViewById(R.id.textOut);
     // Setup the UI
    buttonCalc = (Button)this.findViewById(R.id.buttonCalc);
    buttonCalc.setOnClickListener(new OnClickListener() {
    public void onClick(View v) {
     int v1, v2, res = -1;
     v1 = Integer.parseInt(value1.getText().toString().trim());
     v2 = Integer.parseInt(value2.getText().toString().trim());
     res = nativeLib.add(v1, v2);
     result.setText(new Integer(res).toString());
  13. run ndk-build in command promt

go to project directory-> then, write this command <android-ndk-directory>\ndk-build.cmd and hit enter

after this we can check .so file under obj folder

  1. xml file for NDKActivity.

     <TextView android:layout_width="fill_parent"
    <TextView android:id="@+id/textOut"
    android:hint="Value 1"
    android:inputType="numberDecimal" />
     <TextView android:id="@+id/TextView01"
         android:textSize="36sp" />
       android:hint="Value 2"
       android:inputType="numberDecimal" />
    <Button android:id="@+id/buttonCalc"
    android:text="=" />
    <TextView android:id="@+id/result"
       android:textSize="36sp" />
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