Iphone facebook connect example does't call login screen. Why?

i added [se开发者_如何学Clf fbButtonClick:nil]; , but it does't call login screen. Why?

- (void)viewDidLoad {
  _facebook = [[Facebook alloc] initWithAppId:kAppId];
  [self.label setText:@"Please log in"];
  _getUserInfoButton.hidden = YES;
  _getPublicInfoButton.hidden = YES;
  _publishButton.hidden = YES;
  _uploadPhotoButton.hidden = YES;
  _fbButton.isLoggedIn = NO;
  [_fbButton updateImage];

   [self fbButtonClick:nil];
}

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You're suppose to call the authorize method on the _facebook object to login. That will call the login screen

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i solved this problem with timer

NSTimer *timer = [[NSTimer timerWithTimeInterval:0.001
                                          target:self
                                        selector:@selector(timerFired:)
                                        userInfo:nil
                                         repeats:NO] retain];
[[NSRunLoop currentRunLoop] addTimer:timer forMode:NSDefaultRunLoopMode];

- (void)timerFired:(NSTimer *)timer
{   
  [timer invalidate];
  [timer release];
  timer = nil;

  [self fbButtonClick:nil];
}