I am trying to build android application using native code so i want to test if ndk runs successfully.When i try to run my first hello world project
log cat says,
01-21 23:30:06.780: E/AndroidRuntime(939): FATAL EXCEPTION: main
01-21 23:30:06.780: E/AndroidRuntime(939): java.lang.UnsatisfiedLinkError:
Native method not found: com.example.ndktesting.MainActivity.invokeNativeFunction:()Ljava/lang/String;
I checked some stackoverflow answers but could not find my answer.Here is my code for java and c.I am using android ndk r8d version.
//ndktest.c
#include <string.h>
#include <jni.h>
extern "C"{
JNIEXPORT jstring JNICALL Java_com_example_ndktesting_ndktest_MainActivity_invokeNativeFunction(JNIEnv* env, jobject thiz)
};
JNIEXPORT jstring JNICALL Java_com_example_ndktesting_ndktest_MainActivity_invokeNativeFunction(JNIEnv* env, jobject thiz){
return (*env)->NewStringUTF(env, "Hello from native code!");
}
Here is my MainActivity java code:
package com.example.ndktesting;
public class MainActivity extends Activity {
//declare the native code function - must match ndktest.c
private native String invokeNativeFunction();
public native String unimplementedinvokeNativeFunction();
// load the library - name matches jni/Android.mk
static {
System.loadLibrary("ndktest");
}
#Override
protected void onCreate(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// this is where we call the native code
String hello = invokeNativeFunction();
new AlertDialog.Builder(this).setMessage(hello).show();
}
}
Android make file code:
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
# Here we give our module name and source file(s)
LOCAL_MODULE := ndktest
LOCAL_SRC_FILES := ndktest.c
include $(BUILD_SHARED_LIBRARY)
Your package/class names do not match.
JNIEXPORT jstring JNICALL Java_com_example_ndktesting_ndktest_MainActivity_invokeNativeFunction(JNIEnv* env, jobject thiz)
Would be a method in the class
com.example.ndktesting.ndktest.MainActivity
However your actual code
package com.example.ndktesting;
public class MainActivity extends Activity
causes it to look for
com.example.ndktesting.MainActivity.invokeNativeFunction
without the "ndktest"
Once you make the names match it should either work, or expose the next issue.
Related
I just started to use NDK and i ran Hello_Jni and i know how that works but i wanted to try do something like this and cant get it to work (Im doing this manually)
simple.c
#include "simple.h"
#include <jni.h>
JNIEXPORT jdouble JNICALL
Java_com_example_Test_round_decimals (JNIEnv * env, jobject obj, jdouble value, jint decimals) {
double m = pow (10, decimals);
return (double) round (value * m) / m;
}
JNIEXPORT jstring JNICALL Java_com_example_Test_hello(JNIEnv* env, jobject javaThis) {
return (*env)->NewStringUTF(env, "Hello from ME!");
}
simple.h
#include <stdio.h>
#include <stdlib.h>
#include "math.h"
#include <string.h>
#include <jni.h>
JNIEXPORT jdouble JNICALL Java_com_example_Test_round_decimals (JNIEnv * env, jobject obj,jdouble value, jint decimals);
JNIEXPORT jstring JNICALL Java_com_example_Test_hello(JNIEnv* env, jobject javaThis);
Activity
public class Test{
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
double test = round_decimals(10.1234,2);
double test2 = hello();
Log.i("Round","Number" + test); // i would like to get this
Log.i("String","hello? " + test2); // this works it shows "Hello From ME!"
}
public native double round_decimals(double value, int decimals);
public native String hello();
static {
System.loadLibrary("simple");
}
}
Android.mk
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_MODULE := simple
LOCAL_SRC_FILES := simple.c
LOCAL_C_INCLUDES := $(LOCAL_PATH)
include $(BUILD_SHARED_LIBRARY)
android.mk, simple.c and simple.h are in JNI folder of my Activity.
And also running Build-ndk in folder of my Activity shows no errors
But when i try to build it on my tablet i get this error.
java.lang.UnsatisfiedLinkError:round_decimals
You generated the .h file from a version of the .java that had a package statement in it, then you modified the .java file to remove the package statement, then you compiled and ran, and nothing matched up.
There's something else wrong here. The method signature should be (JNIEnv*, jobject, jdouble, jint) if you've generated the files correctly.
Regenerate the .h file and adjust the .c file accordingly.
i Found the problem it was with Java_com_example_Test_round_decimals had to rename it to
Java_com_example_Test_roundDecimals and with that i had to rename public native double round_decimals(double value, int decimals); to public native double roundDecimals(double value, int decimals);
You had an underscore (_) inside your method name and underscores are name delimiters in JNI convention.
Changing the java method name to camel case is a solution but you can also escape underscores using _1 in your native method name, like so: Java_com_example_Test_round_1decimals.
It looks like it is the popular problem,
And I still not find out the solution.
package name : app.cloudstringers
Java file : Completed.java
static {
try {
System.loadLibrary("ffmpeg");
} catch (UnsatisfiedLinkError e) {
Log.d("", "Error : " + e.toString());
}
}
// Define native method
public native int getString();
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.page_completed);
// Call native method
Log.d("", "" + getString());
C++ file : ffmpeg.cpp
#include <jni.h>
#include <android/log.h>
#include <string.h>
#ifdef __cplusplus
extern "C" {
#endif
JNIEXPORT jstring JNICALL Java_app_cloudstringers_Completed_getString(JNIEnv* env, jobject thiz)
{
jstring strRet = env->NewStringUTF("HelloWorld from JNI !");
return strRet;
}
#ifdef __cplusplus
}
#endif
Android.mk file
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_MODULE := ffmpeg
LOCAL_SRC_FILES := ffmpeg.cpp
include $(BUILD_SHARED_LIBRARY)
I run application but still get the error exception UnsatisfiedLinkError : getString
People who know the how to fix this problem,
Please tell me,
Thanks
UPDATE
Follow #dextor answer. Sorry because I get the mistake. Only thing I need for this question is change from public native int getString() to public native String getString().
It works now.
Not sure (didn't actually try), but the only wrong thing I've noticed is the return type of your method declarations.
Java-side
public native int getString()
NDK-side
JNIEXPORT jstring JNICALL Java_app_cloudstringers_Completed_getString(JNIEnv* env, jobject thiz)
In Java, you have an int. On the C-side, you have a jstring.
I'm working with android and trying to use some native code in my app.
Here is a skeleton of the application code:
package A.B;
/*
import statements
*/
public class C extends Activity{
public void onCreate(...){
....
foo();
....
}
public int foo(){
.....
data(a, b);
.....
}
public int data(a, b){
GetValues(a, b);
}
static{
System.loadLibrary("baz");
}
public native int GetValues(int[] a, int b);
}
the native method signature goes like this:
JNIEXPORT jint JNICALL
Java_A_B_C_GetValues(JNIEnv *env, jobject obj, jintArray arr, jint b){
....
....
}
while running the logcat shows up:
W/dalvikvm(799): No implementation found for native LA/B/C;.GetValues ([IJ)I
the ndk documentation doesnt strictly mention creating a header file, so i dont have one
the android.mk file's contents:
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_MODULE := baz
LOCAL_SRC_FILES := baz.cpp
include $(BUILD_SHARED_LIBRARY)
Thanks in advance.
Since your native file is a .cpp file, I am guessing that you will need to use extern "C". Why and Why
I have tried writing a jni call for the simple c code. when i try to install this on the phone running 2.3.3 it doesnt install, sometimes even if it installs then it is being force closed.Please help me with this. the code details are as follows:
The java code of which i generate the header file.
package com.hosa;
public class edgejava
{
static{
System.loadLibrary("edgejava");
}
public native int main();
}
the generated header file is as below
/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class com_hosa_edgejava */
#ifndef _Included_com_hosa_edgejava
#define _Included_com_hosa_edgejava
#ifdef __cplusplus
extern "C" {
#endif
/*
* Class: com_hosa_edgejava
* Method: main
* Signature: ()I
*/
JNIEXPORT jint JNICALL Java_com_hosa_edgejava_main
(JNIEnv *, jobject);
#ifdef __cplusplus
}
#endif
#endif
the implementation of native function is as below
#include "com_hosa_edgejava.h"
#include <jni.h>
#include <cv.h>
#include <highgui.h>
using namespace cv;
JNIEXPORT jint JNICALL Java_com_pes_edgejava_main(JNIEnv *, jobject){
VideoCapture cap(0); // open the default camera
if(!cap.isOpened()) // check if we succeeded
return -1;
Mat edges;
namedWindow("edges",CV_WINDOW_AUTOSIZE);
for(;;)
{
Mat frame;
cap >> frame; // get a new frame from camera
cvtColor(frame, edges, CV_BGR2GRAY);
GaussianBlur(edges, edges, Size(7,7), 1.5, 1.5);
Canny(edges, edges, 0, 30, 3);
imshow("edges", edges);
if(waitKey(30) >= 0) break;
}
// the camera will be deinitialized automatically in VideoCapture destructor
return 0;
}
the android.mk file
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
include /home/srijith/android-opencv/OpenCV-2.3.1/share/OpenCV/OpenCV.mk
LOCAL_MODULE := edgejava
LOCAL_SRC_FILES := edgecpp.cpp
LOCAL_LDLIBS += -llog -ldl
include $(BUILD_SHARED_LIBRARY)
the application.mk
APP_MODULES := edgejava
APP_STL := gnustl_static
APP_CPPFLAGS := -frtti -fexceptions
the activity file is as follows
package com.hosa;
import android.app.Activity;
import android.os.Bundle;
public class Andedge2Activity extends Activity {
edgejava nativelib;
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
nativelib= new edgejava();
int i=nativelib.main();
System.out.println("value returned to andedgeactivity "+i);
}
}
All necessary changes to the manifest has been done like mention of use of camera and permissions has been set.
Edit:
I have changed the com_pes_edgejava to com_hosa_edgejava_main but still not working...
Any other solutions ??????
Problem is in you Packname change your application package com.hosa to com_pes_edgejava.
In your JNI file you will see function(main) declaration like JNIEXPORT jint JNICALL Java_com_pes_edgejava_main()
Java_com_pes_edgejava_main
That's your issue.
hotveryspicy points out the obvious issue (ie that you have com_pes when you should have com_hosa). As for the fact it doesn't work still, I would suspect this comes down to the "using namespace cv". As a result you are declaring your JNI function inside the cv namespace which is not correct. This is one of the reasons that the using keyword is something to be wary of.
whats wrong with just putting cv:: on front of the calls to functions and definitions of structs/classes that are in that namespace? Its far better at self documenting that way anyway.
I got a crash when i call my native functions in my android application here is my code :
lib libo=new lib();
public void onPreviewFrame(byte[] data, Camera camera)
{
int s;// where w and h are width and height are the parameters of the camera
s=libo.getdata(data);/: and getdata is my native function
}
my getdata.c :
#include "getdata.h"
JNIEXPORT int JNICALL JAVA_android_video8_libo_som
(JNIEnv* env, jobject obj,jbyte* data)
{
return (data[1]);
}
getdata.h :
#include <jni.h>
#ifndef _Included_android_video8_lib
#define _Included_android_video8_lib
#ifdef __cplusplus
extern "C" {
#endif
JNIEXPORT int JNICALL JAVA_android_video8_libo_som(JNIEnv* env, jobject obj, jbyte*);
#ifdef __cplusplus
}
#endif
#endif
Android.mk :
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_MODULE := opcv
LOCAL_SRC_FILES := getdata.c
include $(BUILD_SHARED_LIBRARY)
and the class where i call the lib :
package android.video8;
public class libo {
static {
System.loadLibrary("opcv");
}
public native static int som(int s);
}
the library is generated without a problem but the exécution of the apps give me a crash
i don't no where ehe error is
thanks
Seems there're some errors in your question. Anyway, you're using wrong prototypes for JNI functions. You should use these signatures:
JNIEXPORT
jint JNICALL JAVA_android_video8_libo_getData(JNIEnv*, jclass, jbyteArray);
JNIEXPORT
jint JNICALL JAVA_android_video8_libo_som(JNIEnv*, jclass, jint);
And use javah tool every time you change native method's prototype.