Sometimes the Facebook share dialog doesn't load on iOS

问题

Sometimes when I launch the Facebook share dialog, the OS switches to the Facebook app, but the share dialog doesn't load. Then if you try again, it usually works. Why doesn't it work the first time?

NSURL* url = [NSURL URLWithString:@"some URL"];
FBShareDialogParams* params = [[FBShareDialogParams alloc] init];
params.link = url;
 if ([FBDialogs canPresentShareDialogWithParams:params]) {
     [FBDialogs presentShareDialogWithLink:url
                                   handler:^(FBAppCall *call, NSDictionary *results, NSError *error) {
                                       if(error) {
                                           NSLog(@"Error posting to FB: %@", error.description);
                                           //do something
                                       } else {
                                           //do something else
                                       }
                                   }];
//    }
 }