UIBarbuttonItem不变

Question

我正在尝试使用UIbarbuttonItem来登录/注销Facebook。我可以登录，但无法注销，UIBarbuttonItem标题未更改或启动注销程序。

下面是一些代码：

    - (void)viewDidLoad {

[super viewDidLoad];

   [[NSNotificationCenter defaultCenter]
 addObserver:self
 selector:@selector(sessionStateChanged:)
 name:FBSessionStateChangedNotification
 object:nil];

NSLog(@"Session changed");
AppDelegate *appDelegate =  (AppDelegate *)[[UIApplication sharedApplication] delegate];
[appDelegate openSessionWithAllowLoginUI:NO];
[NSTimer scheduledTimerWithTimeInterval:0.5 target:self selector:@selector(sessionStateChanged:) userInfo:nil repeats:NO];

[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(willBeginBannerViewActionNotification:) name:BannerViewActionWillBegin object:nil];
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(didFinishBannerViewActionNotification:) name:BannerViewActionDidFinish object:nil];

}

    - (IBAction)authButtonAction:(id)sender {
NSLog(@"session open");
AppDelegate *appDelegate = (AppDelegate*)
[[UIApplication sharedApplication] delegate];

// If the user is authenticated, log out when the button is clicked.
// If the user is not authenticated, log in when the button is clicked.
if (FBSession.activeSession.isOpen) {
    [appDelegate closeSession];
} else {
    // The user has initiated a login, so call the openSession method
    // and show the login UX if necessary.
    [appDelegate openSessionWithAllowLoginUI:YES];
}

}

    - (void)sessionStateChanged:(NSNotification*)notification {
NSLog(@"Login Activated");
self.navigationItem.leftBarButtonItem = authButton;
if (FBSession.activeSession.isOpen) {
    self.authButton =[[UIBarButtonItem alloc] initWithTitle:@"Login" style:UIBarButtonItemStyleBordered target:self action:@selector(sessionStateChanged:)];

}else{

    self.authButton =[[UIBarButtonItem alloc]  initWithTitle:@"Logout" style:UIBarButtonItemStyleBordered target:self action:@selector(sessionStateChanged:)];

}

}

日志报告：

    2013-03-18 23:05:58.739 prompT[4056:907] Session changed
    2013-03-18 23:05:58.760 prompT[4056:907] 
    fb sdk error = (null)
    2013-03-18 23:05:58.763 prompT[4056:907] User session found
    2013-03-18 23:05:58.765 prompT[4056:907] Login Activated
    2013-03-18 23:05:59.268 prompT[4056:907] Login Activated
    2013-03-18 23:06:00.872 prompT[4056:907] AdAbanner failed
    2013-03-18 23:06:01.664 prompT[4056:907] Login Activated

我也在使用故事板。有什么想法和帮助吗？

Answer 1

您的sessionStateChanged方法有一些错误，下面是一些注释

  - (void)sessionStateChanged:(NSNotification*)notification {
NSLog(@"Login Activated");

self.navigationItem.leftBarButtonItem = authButton;
       //what is this assignment doing? What is authButton? An iVar?


if (FBSession.activeSession.isOpen) {
    self.authButton =[[UIBarButtonItem alloc] initWithTitle:@"Login" style:UIBarButtonItemStyleBordered target:self action:@selector(sessionStateChanged:)];

  //self.authButton is not the same entity as authButton.
  //did you intend to set authButton here and then 
  //assign it to self.navigationItem.leftBarButtonItem after the conditional?       


}else{

    self.authButton =[[UIBarButtonItem alloc]  initWithTitle:@"Logout" 
               style:UIBarButtonItemStyleBordered 
               target:self action:@selector(sessionStateChanged:)];
    //is this really the action you want, or is it rather `authButtonAction`?

}

这里要做的就是更改按钮的标题：

    - (void)sessionStateChanged:(NSNotification*)notification {
        NSString* buttonTitle = @"Login";
        if (FBSession.activeSession.isOpen) {
            buttonTitle = @"Logout";
        }
        self.navigationItem.leftBarButtonItem.title = buttonTitle;
    }

你应该已经在viewDidLoad或故事板中预先分配、初始化并放置了你的leftBarButtonItem。当您这样做时，您应该正确地挂接IBAction。

代码版本...

- (void) viewDidLoad {
    [super viewDidLoad];
    UIBarButtonItem* barButton =
        [[UIBarButtonItem alloc] initWithTitle:@"login"
                                         style:UIBarButtonItemStyleBordered
                                        target:self
                                        action:@selector(authButtonAction:)];
    self.navigationItem.leftBarButtonItem = barButton;

}