How to show only one AR object at a time on Achor?

Question

i want to show only one object at a time on an achor. Currently i'm getting my AR model from a server at runtime and showing my model. when i tap on anchor pin points every time i got the new AR model so i have to many model after some taps(equals to number of taps). i want restrict the model at once. every time when user taps on the screen ar model always shows only one object at a time.

public class ARObjectActivity extends AppCompatActivity {



private ArFragment arFragment;
private String Asset_3D = "";
String imageUri;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_a_r_object);

    arFragment=(ArFragment) getSupportFragmentManager().findFragmentById(R.id.arFragment);

    Intent intent = getIntent();
    imageUri = intent.getStringExtra("arImageUri");


    arFragment.setOnTapArPlaneListener((hitResult, plane, motionEvent) ->
            placeModel(hitResult.createAnchor()));


}

private void placeModel(Anchor anchor) {

            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N) {

                        ModelRenderable.builder()
                                .setSource(ARObjectActivity.this, RenderableSource.builder()
                                        .setSource(ARObjectActivity.this, Uri.parse(imageUri),
                                                RenderableSource.SourceType.GLTF2)
                                        .setScale(0.5f)
                                        .setRecenterMode(RenderableSource.RecenterMode.ROOT)
                                        .build()
                                )
                                .setRegistryId(Asset_3D)
                                .build()
                                .thenAccept(modelRenderable -> addNoteToScene(modelRenderable,anchor))
                                .exceptionally(throwable -> {
                                    AlertDialog.Builder builder = new AlertDialog.Builder(ARObjectActivity.this);
                                    builder.setMessage(throwable.getMessage()).show();
                                    return null;

                                });



            }


}

private void addNoteToScene(ModelRenderable modelRenderable, Anchor anchor) {

    AnchorNode anchorNode = new AnchorNode(anchor);
    //anchorNode.setRenderable(modelRenderable);
    anchorNode.setParent(arFragment.getArSceneView().getScene());
   // arFragment.getArSceneView().getScene().addChild(anchorNode);

    // Create the transformable andy and add it to the anchor.
    TransformableNode node = new TransformableNode(arFragment.getTransformationSystem());

    //set rotation in direction (x,y,z) in degrees 90
    node.setLocalRotation(Quaternion.axisAngle(new Vector3(1f, 1f, 1f), 90f));

    node.setParent(anchorNode);
    node.setRenderable(modelRenderable);
    node.select();



}
}

Answer 1

Add this new method

private void clearAllModel() {
    List<Node> children = new ArrayList<Node>(arFragment.getArSceneView().getScene().getChildren());
    for (Node node : children) {
        if (node instanceof AnchorNode) {
            AnchorNode tmp = (AnchorNode) node;
            if (tmp.getAnchor() != null) {
                tmp.getAnchor().detach();
            }
        }
    }
}

Then call it at

arFragment.setOnTapArPlaneListener((hitResult, plane, motionEvent) -> {
    clearAllModel();
    placeModel(hitResult.createAnchor()));
}

Explanation:

as you can see, everytime you tap and placeModel into addNoteToScene is called, there is this line of code

anchorNode.setParent(arFragment.getArSceneView().getScene());

all your existing model (which is on anchorNode) is under this arFragment.getArSceneView().getScene() as a child

with my method suggestion, the first time there is 0 child (null). So it will move on and just do placeModel and then it has 1 child. On second time it remove that 1 child, and placeModel is called again, and make it 1 child again. And so on ... so, there will be only 1 child (model)