JNIpp: getting IMEI from native code on Android

gistfile1.cpp

/* There is no native way to get IMEI, so we have to call
 *  Java classes through JNI.
 *
 * But fear not: JNIpp (github.com/DmitrySkiba/itoa-jnipp) makes
 *  this task much easier.
 *
 * To get IMEI we need to perform the following calls:
 *
 * TelephonyManager telephony=(TelephonyManager)
 *   context.getSystemService(Context.TELEPHONY_SERVICE);
 * String id=telephony.getDeviceId();
 */

/* This is 'quick'n'dirty' way of doing the task. JNIpp was designed for
 *  creating wrapper classes, and is not very well suited for ad-hoc
 *  calls. See next file for 'proper' way.
 */

/* There will little explanations, see dmitryskiba.github.com/itoa-jnipp/
 *  for help and examples.
 */

/* Function GetDeviceId() is at the end.
 */

/**************************************/

/* First, implement GetSystemService() function to perform
 *  Context.getSystemService().
 */

#define JB_CURRENT_CLASS Context

JB_DEFINE_ACCESSOR(
    "android/content/Context"
    ,
    NoFields
    ,
    Methods
    (
        GetSysSvc,
        "getSystemService","(Ljava/lang/String;)Ljava/lang/Object;"
    )
)

static java::PObject GetSystemService(java::PObject context,const char* serviceName) {
    return java::PObject::Wrap(
        JB_CALL(ObjectMethod,context,GetSysSvc,java::PString::New(serviceName))
    );
}

#undef JB_CURRENT_CLASS


/**************************************/

/* Then implement TelephonyManager.getDeviceId().
 */

#define JB_CURRENT_CLASS TelephonyManager

JB_DEFINE_ACCESSOR(
    "android/telephony/TelephonyManager"
    ,
    NoFields
    ,
    Methods
    (
        GetDeviceId,
        "getDeviceId","()Ljava/lang/String;"
    )
)

static java::PString GetDeviceId(java::PObject telephony) {
    return java::PString::Wrap(
        JB_CALL(ObjectMethod,telephony,GetDeviceId)
    );
}

#undef JB_CURRENT_CLASS


/**************************************/

/* And finally, put it all together.
 * 'contextObject' is a Context instance, typically an Activity
 *   (if you have NativeActivity object, it is nativeActivity->clazz).
 */
void GetDeviceId(jobject contextObject) {
    java::PObject context=java::PObject::Wrap(contextObject);
    java::PObject telephony=GetSystemService(context,"phone");
    if (!telephony) {
        // Oops, no service.
    } else {
        java::PString idString=GetDeviceId(telephony);
        if (!idString) {
            // We've got NULL
        } else {
            const char* id=idString->GetUTF();
            // Work with id.
        }
    }
}

gistfile2.cpp

/* This correct (as per JNIpp) way of working with Java classes:
 *  you create wrappers for all classes you are interested in
 *  and then your code reads much close to the Java original Java.
 */

void GetDeviceId(jobject contextObject) {
    PContext context=PContext::Wrap(contextObject);
    PTelephonyManager telephony=java::Cast<TelephonyManager>(
        context->GetSystemService(Context::TELEPHONY_SERVICE));
    if (telephony) {
        java::PString id=telephony->GetDeviceId();
        if (id) {
            const char* idUTF=id->GetUTF();
            // Work with id.
        }
    }
}

/**********************************************************/

/* First, declare wrapper classes. This should go in a header file.
 */

class Context: public java::Object {
    JB_WRAPPER_CLASS(Context);
public:
    static const char* const TELEPHONY_SERVICE;
public:
    Context(const jni::LObject& context);
    
    java::PObject GetSystemService(const char* name) const;
};
typedef java::ObjectPointer<Context> PContext;


class TelephonyManager: public java::Object {
    JB_WRAPPER_CLASS(TelephonyManager);
public:
    TelephonyManager(const jni::LObject& telephony);
    
    java::PString GetDeviceId() const;
};
typedef java::ObjectPointer<TelephonyManager> PTelephonyManager;


/**********************************************************/

/* Then implement wrapper classes. This should go in cpp file (or files).
 */

/**************************************/

#define JB_CURRENT_CLASS Context

JB_DEFINE_WRAPPER_CLASS(
    "android/content/Context"
    ,
    NoFields
    ,
    Methods
    (
        GetSysSvc,
        "getSystemService","(Ljava/lang/String;)Ljava/lang/Object;"
    )
)

const char* const Context::TELEPHONY_SERVICE="phone";

Context::Context(const jni::LObject& context):
    java::Object(context)
{
}

java::PObject Context::GetSystemService(const char* name) const {
    return java::PObject::Wrap(
        JB_CALL_THIS(ObjectMethod,GetSysSvc,java::PString::New(name))
    );
}

#undef JB_CURRENT_CLASS

/**************************************/

#define JB_CURRENT_CLASS TelephonyManager

JB_DEFINE_WRAPPER_CLASS(
    "android/telephony/TelephonyManager"
    ,
    NoFields
    ,
    Methods
    (
        GetDeviceId,
        "getDeviceId","()Ljava/lang/String;"
    )
)

TelephonyManager::TelephonyManager(const jni::LObject& telephony):
    java::Object(telephony)
{
}

java::PString TelephonyManager::GetDeviceId() const {
    return java::PString::Wrap(
        JB_CALL_THIS(ObjectMethod,GetDeviceId)
    );
}

#undef JB_CURRENT_CLASS

Just for a great justice. You, actually, can get IMEI from native witout JNI calls. See here.