修改NavigationBarItem的字体大小和颜色的使用方法

//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];