You'll want to use the JNI (Java Native Interface) to call a java method from native. See this post for some sample code that displays a Toast in java when a trackable is found:

http://ar.qualcomm.at/node/2000032

- Kim

ksiva wrote:

You'll want to use the JNI (Java Native Interface) to call a java method from native. See this post for some sample code that displays a Toast in java when a trackable is found:

http://ar.qualcomm.at/node/2000032

- Kim

Thanks Kim for reply. I already seen that post and tried to implement my coding also. As that post based on to show text and my intention to call from native to play video, I finding difficulties here. Anyway I posted my coding here:

ImageTargets.cpp :

JNIEXPORT void JNICALL
Java_com_qualcomm_QCARSamples_ImageTargets_ImageTargetsRenderer_renderFrame(JNIEnv* env, jobject obj)
{
. . . . .
for(int tIdx = 0; tIdx {

int textureIndex = (!strcmp(trackable->getName(), "stone")) ? 0 : 1;
const Texture* const thisTexture = textures[textureIndex];
jstring js = env->NewStringUTF(trackable->getName());
jclass javaClass = env->GetObjectClass(obj);
jmethodID method = env->GetMethodID(javaClass, "displayMessage", "(Ljava/lang/String;)V");
env->CallObjectMethod(obj, method, js);

}

ImageTargets.java :

public static Handler mainActivityHandler;

//calling my video playback code from here
public void displayMessage(String text)
{
Intent intent = new Intent(this,MediaPlayerDemo_Video.class);
intent.putExtra(MEDIA,LOCAL_VIDEO);
startActivity(intent);

}

protected void onResume()
{
ImageTargetsRenderer.mainActivityHandler = new Handler() {
public void handleMessage(Message msg) {
. . . . . . . .
//don’t know what to written here as the mentioned code for showing text
}

It’s successfully built and installed in phone. But after detect the marker, the program exit automatically. As the given[post] code for showing text, so can you help me to convert the coding to call from native to play video… Under display message function, my video code is there.

Thanks
Rassall

You can probably skip the Handler here. Try storing the activity context in the ImageTargetsRenderer class:

ImageTargets.cpp

int lastTrackableId = -1;

JNIEXPORT void JNICALL
Java_com_qualcomm_QCARSamples_ImageTargets_ImageTargetsRenderer_renderFrame(JNIEnv* env, jobject obj)
{
    ...
    
    // Did we find any trackables this frame?
    for(int tIdx = 0; tIdx < state.getNumActiveTrackables(); tIdx++)
    {
        // Get the trackable:
        const QCAR::Trackable* trackable = state.getActiveTrackable(tIdx);
        
        // Compare this trackable's id to a globally stored id
        // If this is a new trackable, find the displayMessage java method and
        // call it with the trackable's name
        if (trackable->getId() != lastTrackableId) {
            jstring js = env->NewStringUTF(trackable->getName());
            jclass javaClass = env->GetObjectClass(obj);
            jmethodID method = env->GetMethodID(javaClass, "playVideo", "(Ljava/lang/String;)V");
            env->CallVoidMethod(obj, method, js);
            lastTrackableId = trackable->getId();
        }
        
        ...
    }
    
    ...
}

ImageTargetsRenderer.java

    // Store the activity context
    public static Context context;
    
    // Called from native to play a video
    public void playVideo(String trackableName)
    {
    	Intent intent = new Intent(context,MediaPlayerDemo_Video.class);
    	intent.putExtra(MEDIA,LOCAL_VIDEO);
    	context.startActivity(intent);
    }

ImageTargets.java

    protected void onResume()
    {
        super.onResume();
        
        ImageTargetsRenderer.context = this;
        
        ...
    }

Note I changed CallObjectMethod to CallVoidMethod in the JNI section, someone pointed out that this is the correct way to do it.

- Kim

Thanks Kim...

It's now working as expected...

Regards

Rassall

I used the similar method in VirtualButtons, i would like to play a video when the user press the virtual button, but it doesn't work in this scenario. Below is my code:

VirtualButtons.cpp

Check same question here:

https://developer.vuforia.com/forum/android/adding-virtual-buttons-videoplayback