Android - using JNI FindClass to find a Java class fails

Hi,

The following pieces of code behave differently:

A.
    void test_a() // called from main function
    {
        QAndroidJniEnvironment jniEnv;

        jclass j_info_class = jniEnv->FindClass("xxx/yyy/zzz/MyClass");
 
        if ( j_info_class ) {
            qDebug() << "j_info_class is valid";
        } else {
            qDebug() << "j_info_class is invalid";
        }
        //...
    }
    The value of j_info_class is nullptr, printing “j_info_class is invalid”.

and

B.
    void test_b() // called from main function
    {
        if (QAndroidJniObject::isClassAvailable("xxx/yyy/zzz/MyClass")) {
            qDebug() << "Available";
        }
    }

Prints “Available”

So, the Java class was found in test_b() but wasn't found in test_a().

Note: I need to use the test_a() code (FindClass) because I am using a shared library (I can not modify the code) that uses JNI that way.

These are the configuration steps I followed:

1. I put the .jar file into android/libs directory.
When I run in debug mode I could check that the JAR is copied into: build-myProjectName-Platform-Debug/android-build/libs

2. I put this in the AndroidManifest.xml
<meta-data android:name=“android.app.load_local_jars” android:value=“jar/QtAndroid.jar:jar/QtAndroidAccessibility.jar:jar/QtAndroid-bundled.jar:jar/QtAndroidAccessibility-bundled.jar:jar/myjar.jar”/>

Note: The “jar/QtAndroid.jar:jar/QtAndroidAccessibility.jar:jar/QtAndroid-bundled.jar:jar/QtAndroidAccessibility-bundled.jar” part was copied from the original AndroidManifest.xml created by the QtCreator.

Regards,
Fernando.

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Hi,

I have a legacy JAR (java code) and a legacy shared library (C++) that uses JNI to "talk with JAR".

I have the following example code:

A.
    jclass code_on_the_shared_library(JNIEnv* jni)
    {
        return jni->FindClass("xxx/yyy/zzz/MyClass");
    }
    // ...

    void code_in_the_qt_executable() // called from main function
    {
        QAndroidJniEnvironment jniEnv;

        jclass j_info_class = function_on_the_shared_library(jniEnv);
 
        if ( j_info_class ) {
            qDebug() << "j_info_class is valid";
        } else {
            qDebug() << "j_info_class is invalid";
        }
    }
    The value of j_info_class is nullptr, printing “j_info_class is invalid”.

On the other hand, I did the following test

B.

if (QAndroidJniObject::isClassAvailable("xxx/yyy/zzz/MyClass")) {
    qDebug() << "Available";
}

Prints “Available”

These are the configuration steps:

I am following the following steps:

1. I put the .jar file into android/libs directory.

When I run in debug mode I could check that the JAR is copied into: build-myProjectName-Platform-Debug/android-build/libs
2. I put this in the AndroidManifest.xml

<meta-data android:name=“android.app.load_local_jars” android:value=“jar/QtAndroid.jar:jar/QtAndroidAccessibility.jar:jar/QtAndroid-bundled.jar:jar/QtAndroidAccessibility-bundled.jar:jar/myjar.jar”/> Note: The “jar/QtAndroid.jar:jar/QtAndroidAccessibility.jar:jar/QtAndroid-bundled.jar:jar/QtAndroidAccessibility-bundled.jar” part was copied from the original AndroidManifest.xml created by the QtCreator.

Thanks and regards,
Fernando.