QJniObject.callObjectMethod "getString" on android.os.Bundle Returns "" Despite Bundle.toString() Showing Value

[KenAppleby 0]

I have an android.os.Bundle which is passed to C++ from Java via a native function call. The received object, when printed with .toString() appears to contain all the expected values.

static ReceivedFileDetails fromBundle(QJniObject bundle)  {
  qDebug() << "ReceivedFileDetails::fromBundle" << bundle.toString();

=> ReceivedFileDetails::fromBundle "Bundle[{my.package.aat.Bundle.Flags=50331649, my.package.aat.Bundle.Action=android.intent.action.VIEW, my.package.aat.Bundle.Scheme=content, my.package.aat.Bundle.Subject=null, my.package.aat.Bundle.Uri=content://com.google.android.apps.nbu.files.provider/2/1000001836, my.package.aat.Bundle.Data=content://com.google.android.apps.nbu.files.provider/2/1000001836, my.package.aat.Bundle.Path=null, my.package.aat.Bundle.Text=null, my.package.aat.Bundle.Type=application/octet-stream}]"

But I can't find a way to extract the individual values via QJniObject.callObjectMethod calls, for example:

jstring actionKey = QJniObject::fromString("my.package.aat.Bundle.Action").object<jstring>();
QString action = bundle.callObjectMethod("getString", "(Ljava/lang/String;)Ljava/lang/String;", actionKey).toString();
qDebug() << "action" << action;

=> action ""

The returned value is always "".
Please can anyone tell me what I am doing wrong?

Thanks.

[JoeCFD]

It may be your Java code is not made properly. Can you show your Java function?
Use new to create the return String in your Java code.

[KenAppleby 0]

@JoeCFD
This is the Java code, simplified:

// ReceivedFileDetails is a Java class to hold parameters from the Intent
public class ReceivedFileDetails {
    public static final String Action = "my.package.aat.Bundle.Action";
    public String mAction;
    public Bundle getBundle() {
        Bundle bundle = new Bundle();
         if (mAction != null) { 
            bundle.putString(Action, new String(mAction));
        }
        return bundle;
    }
    public static native void sendNativeBundle(Bundle bundle); // the native call to pass the Bundle to C++
}

// In Activity.onCreate():
    mDetails = new ReceivedFileDetails();
    mDetails.mAction = getIntent().getAction();
    Bundle bundle = mDetails.getBundle();
    ReceivedFileDetails.sendNativeBundle(bundle);

When I first posted about this the code to insert the Action into the Bundle did not instantiate a new String. The new code, even with the new String(...) still gives "" for the return value from .Bundle.getString JNI call.

Thanks.

[JoeCFD]

Not sure if what you did is right or not. How did you get bundle in in the following Qt code?
QString action = bundle.callObjectMethod("getString", "(Ljava/lang/String;)Ljava/lang/String;", actionKey).toString();
I guess you may not need to pass bundle to Qt code. Instead send back only a string.

This is what I did and it works.

    auto info_obj = QAndroidJniObject::callStaticObjectMethod( "java class name with path",
                                                               "static func name",
                                                               "(Landroid/content/Context;)Ljava/lang/String;",
                                                               QtAndroid::androidContext().object() );

    auto info_str = info_obj.toString();

[KenAppleby 0]

@JoeCFD
The Bundle comes in effectively like this:

static void receivedFileBundle(JNIEnv *env, jobject thiz, jobject jbundle)
{
    QJniObject bundle(jbundle);
    qDebug() << "receivedFileBundle:" << bundle.toString();
    jstring actionKey = QJniObject::fromString("my.package.aat.Bundle.Action").object<jstring>();
    QString action = bundle.callObjectMethod("getString", "(Ljava/lang/String;)Ljava/lang/String;", actionKey).toString();
    qDebug() << "action" << action;
}

const JNINativeMethod methods[] {
    { "sendNativeBundle", "(Landroid/os/Bundle;)V",
        reinterpret_cast<void *>(aat::ReceivedFileDetailsJavaClass::receivedFileBundle) },
    };
    
    sEnv.registerNativeMethods("my/package/aat/ReceivedFileDetails", methods, 1);

// Java: In Activity.onCreate():
    mDetails = new ReceivedFileDetails();
    mDetails.mAction = getIntent().getAction();
    Bundle bundle = mDetails.getBundle();
    ReceivedFileDetails.sendNativeBundle(bundle);

I have since moved past this passing a String (Json) instead of a Bundle, and it works fine, as you say. But it would be good to know why using a Bundle doesn't work.

I note that "getString" is not a method of android.os.Bundle but of android.os.BaseBundle, but I doubt that that is the reason.

[JoeCFD]

@KenAppleby-0 QJniObject has limited types to handle. Bundle is not one of them. Check out what QJniObject can handle.
Scroll all way down and look for JNI Types
https://doc.qt.io/qt-6/qjniobject.html

[KenAppleby 0]

@JoeCFD

So C++ bundle.toString() calls a Java method on java.lang.Object, via jobject, which is a supported JNI type.

That explains it.

Thank you.