How to call Java function with int parameter from JNI

Question

I have a static Java function in an Activity. This function has int parameter. I want to call this function from JNI. I use below code to call, but I don't know how to pass int parameter:

In Java:

public static void updateTopScoreLeaderboard(int score) {
    Log.i("", "updateTopScoreLeaderboard " + score);
}

In JNI:

if (JniHelper::getStaticMethodInfo(methodInfo, "com/nch/myApp/MyActivity", "updateTopScoreLeaderboard", "()V"))
{
    methodInfo.env->CallStaticObjectMethod(methodInfo.classID, methodInfo.methodID);
}
methodInfo.env->DeleteLocalRef(methodInfo.classID);

That code work well if Java function has no param. But in this case (has int param), it not work.

323go · Accepted Answer · 2014-02-12 16:57:51Z

5

You need to change the method signature to match the int parameter, so it's (I)V instead of ()V, and also add your int parameter to the method invocation:

int myInt = 0;

if (JniHelper::getStaticMethodInfo(methodInfo, "com/nch/myApp/MyActivity", "updateTopScoreLeaderboard", "(I)V"))
{
    methodInfo.env->CallStaticObjectMethod(methodInfo.classID, methodInfo.methodID, myInt );
}
methodInfo.env->DeleteLocalRef(methodInfo.classID);

answered Feb 12, 2014 at 16:57

323go

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3 Comments

Tom Blodget Over a year ago

@huync To find signatures use javap. For example, javap -s -public com/nch/myApp/MyActivity | egrep -A 2 "updateTopScoreLeaderboard". Just as in running java, the code needs to be compiled first and be sure to pass in a classpath if needed.

huynguyen Over a year ago

That is a great answer.

Lyubomir Vasilev Over a year ago

You should call CallStaticVoidMethod, instead of CallStaticObjectMethod, since the Java method returns void, and not an object.

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