GADBannerView设置背景图片

在加载广告的时候如何设置背景图片？只要显示到广告加载完即可。

AdMob = [[GADBannerView alloc]init];
AdMob.frame = CGRectMake(0, 0 , GAD_SIZE_300x250.width, GAD_SIZE_300x250.height);
AdMob.backgroundColor = [UIColor grayColor];
AdMob.adUnitID = [GlobalVariable sharedInstance].PID_IOS_PHONE;
AdMob.rootViewController = self;
GADRequest *request = [GADRequest request];
[AdMob loadRequest:request];

如下设置背景：

AdMob.backgroundColor = [UIColor colorWithPatternImage:[UIImage imageNamed:@"Background.png"]];