#define SYSTEM_VERSION_MORE_THAN_BFDATA(v)  ([[[UIDevice currentDevice] systemVersion] compare:v options:NSNumericSearch] == NSOrderedDescending)+ (NSString *)advertisingID {        NSString *returnValue = nil;    if (SYSTEM_VERSION_MORE_THAN_BFDATA(@"5.9")) {//通过抽象类来获取 ASIdentifier 这里面的方法。得到idfa        Class MyManager = NSClassFromString(@"ASIdentifierManager");        if (MyManager) {            id manager = [MyManager performSelector:@selector(sharedManager)];            if ([manager performSelector:@selector(isAdvertisingTrackingEnabled)]) {                returnValue = [[manager performSelector:@selector(advertisingIdentifier)]                               performSelector:@selector(UUIDString)];            }        }    }        return returnValue;}