UIActivityViewController Facebook共享视图立即消失

Question

UIActivityViewController Facebook共享视图立即消失，与facebook分享立即查看disappers。

NSArray *activityItems = @[[NSURL URLWithString:_shareurl];
_controller = [[UIActivityViewController 
alloc]initWithActivityItems:activityItems

applicationActivities:nil];
    _controller.excludedActivityTypes = @[UIActivityTypePrint,                                             
UIActivityTypeCopyToPasteboard,                                             
UIActivityTypeAssignToContact,                                             
UIActivityTypeSaveToCameraRoll,
UIActivityTypeAirDrop,
UIActivityTypePostToVimeo,
UIActivityTypePostToFlickr
UIActivityTypeAddToReadingList];
    [self presentViewController:_controller animated:YES 
completion:^{
  _controller.completionWithItemsHandler = ^(NSString *activityType, 
BOOL completed, NSArray *returnedItems, NSError *activityError) {
if ([activityType 
isEqualToString:@"com.apple.reminders.RemindersEditorExtension"])
                   {
                   }
                   else{

                   }
    };
 }];