create instance of android.accounts.Account in qt c++ code

Question

I am trying to use the android AccountManager from qt c++ code. To add a account, I want to create an instance of android.accounts.Account, I am trying to do this with this code:

jstring jUsername = QAndroidJniObject::fromString(username).object<jstring>();
jstring jPassword = QAndroidJniObject::fromString(password).object<jstring>();
jstring jType = QAndroidJniObject::fromString(type).object<jstring>();
qDebug()<<"Creating";
QAndroidJniObject accountObject("android.accounts.Account","(Ljava/lang/String;Ljava/lang/String;)V",jUsername,jType);
qDebug()<<"Inserting";

The code segfaults at the line, where the accountObject is created ("Creating" is printed, "Inserting" not):

JNI ERROR (app bug): accessed deleted global reference 0x100e46
JNI ERROR (app bug): accessed deleted global reference 0xe46

I read this occurs, if I call a method with a wrong signature, but the signature is right (see here).

Answer 1

By the looks of it, the way you're creating your strings are causing your problem.

jstring jUsername = QAndroidJniObject::fromString(username).object<jstring>();

What this does is create an anonymous temporary QAndroidJniObject (returned by fromString), which you then extract the wrapped jobject from (and cast it to a jstring). By the time execution of that statement finishes the lifetime of that QAndroidJniObject is over, and the reference it held to the wrapped jobject will be released.

You could change your code to somethine like this:

auto qjUsername = QAndroidJniObject::fromString(username);
auto jUsername = qjUsername.object<jstring>();

Or to:

jstring jUsername = env->NewLocalRef(QAndroidJniObject::fromString(username).object<jstring>());

Assuming that you have a way of getting the JNIEnv*. If you create a new reference you should probably also delete it with DeleteLocalRef when you don't need it anymore.