iPhone SDK-导航控制器pushViewController-无响应

我有一个视图,它有一个navigationController,有两个按钮,开始(基本上是一个登录按钮)和设置。单击“设置”时,将显示“设置”视图,并按计划取消。我可以单击“设置”,然后多次单击“上一步”,而不会导致任何崩溃。好的

问题是,一旦我从登录按钮切换到注销按钮再切换到登录按钮,设置按钮就会停止工作。SHOWSETTINGS方法会触发并运行-不会发生错误-但不会显示视图。

任何帮助都将不胜感激!!

-(void)showLoginButtons{
    self.navigationItem.rightBarButtonItem=[[UIBarButtonItem alloc] initWithTitle:@"Settings" style:UIBarButtonItemStylePlain target:self action:@selector(showSettings)];
    self.navigationItem.leftBarButtonItem=[[UIBarButtonItem alloc] initWithTitle:@"Start" style:UIBarButtonItemStylePlain target:self action:@selector(tryConnection)];
}

-(void)showLogoffButtons{
    self.navigationItem.rightBarButtonItem=nil;
    self.navigationItem.leftBarButtonItem=[[UIBarButtonItem alloc] initWithTitle:@"Logoff" style:UIBarButtonItemStylePlain target:self action:@selector(resetConnectionAndScreen)];
}

-(void)showSettings{
    SettingsViewController *mySettingsViewController= [[SettingsViewController alloc] initWithNibName:@"SettingsViewController" bundle:nil];
    iPhone_PNPAppDelegate *mainDelegate = (iPhone_PNPAppDelegate *)[[UIApplication sharedApplication] delegate];
    mySettingsViewController.settings=mainDelegate.settings;
    [[self navigationController] pushViewController:mySettingsViewController animated:YES];
    [mySettingsViewController release];
}