How to get notified when MPTableViewAdPlacer finished downloading an ad

[toole]

How do I get a notification/delegate call that an ad was downloaded using the following code to get an ad:

MPServerAdPositioning *positioning = [[MPServerAdPositioning alloc] init];

    self.placer = [MPTableViewAdPlacer placerWithTableView:self.tableView viewController:self adPositioning:positioning defaultAdRenderingClass:[AdListCell class]];

[self.placer loadAdsForAdUnitID:@"xxxxx" targeting:[self targetingForAdWithPrice]];