var myLayer = new ol.layer.Vector ... // from returned GeoJSON

searchResults.setLayers(new ol.Collection([myLayer]));  // add the layer to a layergroup which is already bound to the map
myLayer.setVisible(true);  // the layer shows up keeping the initial mapview
var extent=parzellen.getSource().getExtent();
alert (extent);  // at this point alert shows me Infinity,Infinity,-Infinity,-Infinity
map.getView().fit(extent, map.getSize());  // this never happens

myLayer.on('change',function(e){
      if(myLayer.getSource().getState() === 'ready') {
        if(myLayer.getSource().getFeatures().length>0) {
          searchResults.setLayers(new ol.Collection([myLayer]));
          myLayer.setVisible(true);
          map.getView().fit(myLayer.getSource().getExtent(), map.getSize());
        }
      }
    });