//创建一个左边按钮    UIBarButtonItem *leftButton = [[UIBarButtonItem alloc] initWithTitle:@"<" style:UIBarButtonItemStylePlain target:self action:@selector(clickLeftButton)];    //    leftButton.        [leftButton setTitleTextAttributes:[NSDictionary dictionaryWithObjectsAndKeys:                                        [UIFont fontWithName:@"Helvetica-Bold" size:17.0], NSFontAttributeName,                                        [UIColor greenColor], NSForegroundColorAttributeName,                                        nil]                              forState:UIControlStateNormal];    //创建一个右边按钮    UIBarButtonItem *rightButton = [[UIBarButtonItem alloc] initWithTitle:@"登陆" style:UIBarButtonItemStyleDone target:self action:@selector(clickRightButton)];    [rightButton setTitleTextAttributes:[NSDictionary dictionaryWithObjectsAndKeys:                                         [UIFont fontWithName:@"Helvetica-Bold" size:17.0], NSFontAttributeName,                                         [UIColor greenColor], NSForegroundColorAttributeName,                                         nil]                               forState:UIControlStateNormal];