Waiting for the BusyIndicator, this can be easily achieved watching the property "updating" of your view and dojo Toggler
loading = new Toggler({
node: "loadingImg"
});
app.mapView.watch("updating", function (updating) {
updatingViewChange(updating);
});
function updatingViewChange(updating)
{
if (updating) {
loading.show();
}
else {
loading.hide();
}
}