How to create a string array using JNI in Qt

Question

I have to write some Android platform specific code in Qt and need to use JNI. I have a problem with how to create an array of some object. In this case I want to construct an array of strings from C++.

In the two code snippets below the first one creates a java string and it works as expected. In the second code snippet I want to create a java string array, but I get the debug message: "Java string array not valid" so I assume the signature and/or parameters passed to the "QAndroidJniObject javaStringArray()" function is not correct.

I have been looking at the documentation, but was not able to find or properly understand how to do this.

I assume I have to send in the size of the java string array object I want to construct as well.

Any help is appreciated!

QAndroidJniObject javaString("java/lang/String");
if (!javaString.isValid()) {
    qDebug() << "Java string not valid";
    return false;
}

QAndroidJniObject javaStringArray("[Ljava/lang/String;");
if (!javaStringArray.isValid()) {
    qDebug() << "Java string array not valid";
    return false;
}

jpnurmi · Accepted Answer · 2016-07-10 18:54:23Z

3

The QAndroidJniObject constructor you are using takes a class name, so I'm afraid passing a string array signature won't work. You'll probably have to get your hands dirty and call JNI NewObjectArray(). Try something like:

QAndroidJniEnvironment env;
jobjectArray stringArray = env->NewObjectArray(5, env->FindClass("java/lang/String"), NULL);
QAndroidJniObject jniArray = QAndroidJniObject::fromLocalRef(stringArray);
// ...

This would create an array of 5 null strings, and transfer the ownership to QAndroidJniObject if you prefer, or else you'll have to take care of calling DeleteLocalRef().

edited Jul 10, 2016 at 18:54

answered Jul 10, 2016 at 18:48

jpnurmi

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