Updating data in dc

For my first device (watch) app, I would like to display some data in my view. As an example, I enabled Position on start of the app and defined the onPosition() method:

class MyApp extends Application.AppBase {

    ...
    
    var myView;

    // onStart() is called on application start up
    function onStart(state) {
        Position.enableLocationEvents(Position.LOCATION_CONTINUOUS, method(:onPosition));
    }
    
    function onPosition(info) {
    	var pos = info.position.toDegrees();
    	myView.updatePosition(pos[1], myView.findDrawableById("PositionLayer"));
    }
    
    ...
    
}

where updatePosition(pos,layer) is a method of myView. As you can see, I try to access the layer "PositionLayer" which I added in onLayout(dc). Then in this updatePosition method, I would like to update the position data like this:

class MyView extends Ui.View {

    ...
    
    function onLayout(dc) {
        var positionLayer = new Ui.Layer({:locX=>22, :locY=>60, :width=>120, :height=>20, :identifier=>"PositionLayer"});
        addLayer(positionLayer);
    }
    
    function updatePosition(pos, lay) {
        var dc = lay.getDc();
        dc.setColor(foregroundColor, backgroundColor);
        dc.drawText(0, 0, Gfx.FONT_XTINY, position.format("%d"), Gfx.TEXT_JUSTIFY_LEFT);	
    }
    
    ...
    
}

Apparently, myView.findDrawableById("PositionLayer") does not work. I guess that a layer is not a drawable. However, I wonder, why there is the possibility of adding an identifier to a layer, if it cannot be accessed.

So my question is, how shall I update the PositionLayer appropriately? Probably, Ui.requestUpdate() might be suited in general but this obviously does not transfer the new position data. Is there a better way for this? Shall I simply use drawables instead of layers?