Ndk build and .so android file creation

Question

I am new to android ndk.

I am working on an application that needs Java code as well as c / C ++ code

So, for this I need android ndk.

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

So. please help me solve this problem.

I tried on both Windows and Linux but got the 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 1

First of all, you get this error because you are not declaring the in parameter, you need to create a connection between java and c / C ++.

SO, I am sending you my code for your problem

1. First of all, create an android project in eclipse.

2. create a folder under the project click → click new → then the folder and name it jni.

3. create another folder named jni.

4. create java class.

5. code for class name java- (MainActivity.java) →

     package com.example.ndk; import android.os.Bundle; import android.app.Activity; import android.view.Menu; public class MainActivity extends Activity { static { System.loadLibrary("myjni"); } /** * Adds two integers, returning their sum */ public native int add( int v1, int v2 ); /** * Returns Hello World string */ public native String hello(); @Override 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; } } 

6. open a command prompt or press + R.

7. go to the directory- (workspace-> project name → jni → enable).

8. execute the command in this directory.

     javah -classpath <project-name>/bin/classes;<ANDROID_SDK_HOME>\platforms\android-<xx>\android.jar -o HelloJNI.h com.example.test.MainActivity 

9. after that we can see the HelloJNI.h file in the include folder.

10. check "HelloJNI.h" in this text

     JNIEXPORT jint JNICALL Java_com_example_ndk_MainActivity_add(JNIEnv *, jobject, jint, jint); JNIEXPORT jstring JNICALL Java_com_example_ndk_MainActivity_hello (JNIEnv *, jobject); 

11. create a new file under jni naming test.c (use this 2 points in pont 10 in this test.c file)

      #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); } 

12. create a new file named jni name 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) 

13. create a new NDKActivity.java file

      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) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); 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); outText.setText(helloText); // 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()); } }); } } 

14. run ndk-build in the promt command

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

after that we can check the .so file in the obj folder

14. xml file for NDKActivity.

      <TextView android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="Vikram" android:textSize="22sp"/> <TextView android:id="@+id/textOut" android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="Output"/> <EditText android:id="@+id/value1" android:layout_width="fill_parent" android:layout_height="wrap_content" android:hint="Value 1" android:inputType="numberDecimal" /> <TextView android:id="@+id/TextView01" android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="+" android:textSize="36sp" /> <EditText android:id="@+id/value2" android:layout_width="fill_parent" android:layout_height="wrap_content" android:hint="Value 2" android:inputType="numberDecimal" /> <Button android:id="@+id/buttonCalc" android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="=" /> <TextView android:id="@+id/result" android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="result" android:textSize="36sp" /> </LinearLayout> 

Answer 2

This seems to be a mis-match function in the .h and .cpp file. You mentioned some parameters in the functions in the .h file that are not in the implementation in the native.cpp files.