Android ICS 4.0 NDK NewStringUTF is crashing down the App

Question

I have a method in JNI C/C++ which takes jstring and returns back jstring some thing like as below,

  NATIVE_CALL(jstring, method)(JNIEnv * env, jobject obj         


        

Answer 1

For me, the solution was to place the content on a const char*:

const char* string = name_sin.c_str();
jstring utf8 = env_r->NewStringUTF(string);

and the function:

jclass cls_Env = env_r->FindClass(CLASS_ACTIVITY_NAME); 
jmethodID mid = env_r->GetMethodID(cls_Env, "Delegate",
                                 "(Ljava/lang/String;)V");


//todo importante hacerlo asi, si pasas directamente c_str a veces da error de carater no UTF 8
const char* string = name_sin.c_str();
jstring utf8 = env_r->NewStringUTF(string);

env_r->CallVoidMethod(*object_r, mid, utf8);

env_r->DeleteLocalRef(utf8);

Answer 2

This works for me in c++

extern "C" JNIEXPORT
jstring Java_com_example_ndktest_MainActivity_TalkToJNI(JNIEnv* env, jobject javaThis, jstring strFromJava)
{
    jboolean isCopy;
    const char* szHTML = env->GetStringUTFChars(strFromJava, &isCopy);

    std::string strMine;
    strMine = szHTML;
    strMine += " --- Hello from the JNI!!";

    env->ReleaseStringUTFChars(strFromJava, szHTML);
    return env->NewStringUTF(strMine.c_str());
}

Answer 3

This is how I done this.

1- Char Array to JByteArray.

2- JByteArray to JString.

3- Return jstring to java side.

JNI Code; (.c) format

jstring Java_com_x_y_z_methodName(JNIEnv *env, jobject thiz) {
    int size = 16;
    char r[] = {'P', 'K', 'd', 'h', 't', 'X', 'M', 'm', 'r', '1', '8', 'n', '2', 'L', '9', 'K'};
    jbyteArray array = (*env)->NewByteArray(env, size);
    (*env)->SetByteArrayRegion(env, array, 0, size, r);
    jstring strEncode = (*env)->NewStringUTF(env, "UTF-8");
    jclass cls = (*env)->FindClass(env, "java/lang/String");
    jmethodID ctor = (*env)->GetMethodID(env, cls, "<init>", "([BLjava/lang/String;)V");
    jstring object = (jstring) (*env)->NewObject(env, cls, ctor, array, strEncode);

    return object;
}

Java Code;

native String methodName();

Other Approach Not Works For Me;

I also tried return (*env)->NewStringUTF(env, r) but returns some characters that are not in the char array, at the end of the string where with the warning of JNI WARNING: input is not valid Modified UTF-8: illegal continuation byte 0x40.

Example; PKdhtXMmr18n2L9K�ؾ�����-DL

Edit:

C++ version

jstring clientStringFromStdString(JNIEnv *env,const std::string &str){
//    return env->NewStringUTF(str.c_str());
    jbyteArray array = env->NewByteArray(str.size());
    env->SetByteArrayRegion(array, 0, str.size(), (const jbyte*)str.c_str());
    jstring strEncode = env->NewStringUTF("UTF-8");
    jclass cls = env->FindClass("java/lang/String");
    jmethodID ctor = env->GetMethodID(cls, "<init>", "([BLjava/lang/String;)V");
    jstring object = (jstring) env->NewObject(cls, ctor, array, strEncode);
    return object;
}

Answer 4

I also struggled with the same problem from the last day. Finally figured out a solution after a day .. I hope this reply may save someone's day..

The problem was I was calling another function within the native function, used the returned string directly and which caused crash in android older versions

So firstly I saved the string returned from another function to a variable then used it, and the problem gone :D

The below example may clear your concept

//older code with error
//here key_ is the string from java code

const char *key = env->GetStringUTFChars(key_, 0);
const char *keyx = getkey(key).c_str();
return env->NewStringUTF(keyx);

And here is how I solved this error

//newer code which is working
//here key_ is the string from java code

const char *key = env->GetStringUTFChars(key_, 0);
string k = getkey(key);
const char *keyx = k.c_str();
return env->NewStringUTF(keyx);

Happy coding :D