导航条的使用 UINavigationBar

导航条继承与UIView，且通常只是作为多个UINavigationItem的容器，而且他以Stack的形式来管理多个UINavigationItem的控件，这意味着导航条上每次只能看到一个UINavigationItem对象。

在同一时刻，只能看到最上面的UINavigationItem，UINavigationBar最底层的控件被称作root UINavigationItem;

方法：

-pushNavigationItem: animated:该方法将一个UINavigationItem压入UINavigationBar的栈中

- (void)setItems:(nullable NSArray<UINavigationItem *> *)items animated:(BOOL)animated;同事为导航条设置多个UINavigationItem控件

- (nullable UINavigationItem *)popNavigationItemAnimated:(BOOL)animated;

topItem: 用于返回UINavigationItem控件最顶层的UINavigationItem

backItem:用于返回UINavigationItem控件最顶层下面的UINavigationItem

UINavigationItem也作为一个容器，他的组成就不用说了，相信大家都知道，那我们看看不怎么了解的属性：

hidesBackButton:该属性用于设置或返回是否显示后退按钮。如果将该属性设置为YES,那么就会隐藏后退按钮。

下方通过代码了解UINavigationIBar

//

#import "ViewController.h"

@interface ViewController ()
{
    //记录当前是添加第几个UINavigationItem的计数器
    NSInteger count;
    UINavigationBar *navigationBar;
}

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    
    
    count = 1;
    //创建导航条
    navigationBar = [[UINavigationBar alloc]initWithFrame:CGRectMake(0, 20, self.view.frame.size.width, 44)];
    [self.view addSubview:navigationBar];
    //调用push方法添加一个UINavigationItem
    [self push];
}
-(void)push
{
    //把导航栏集合添加到导航栏中，设置动画打开
    [navigationBar pushNavigationItem:[self makeNavItem] animated:YES];
    count ++;
}
-(void)pop
{
    if (count > 2) {
        count--;
        //弹出最顶层的UINavigationItem
        [navigationBar popNavigationItemAnimated:YES];
    }else{
        UIAlertView *alert = [[UIAlertView alloc]initWithTitle:@"提示" message:@"只剩下最后一个导航项，再出栈就没有了" delegate:self cancelButtonTitle:@"OK" otherButtonTitles: nil];
        [alert show];
    }
    
}
-(UINavigationItem *)makeNavItem
{
    //创建一个导航项
    UINavigationItem *navigationItem = [[UINavigationItem alloc]init];
    UIBarButtonItem *leftButton = [[UIBarButtonItem alloc]initWithBarButtonSystemItem:UIBarButtonSystemItemAdd target:self action:@selector(push)];
    UIBarButtonItem *rightButton =[[UIBarButtonItem alloc]initWithBarButtonSystemItem:UIBarButtonSystemItemCancel target:self action:@selector(pop)];
    navigationItem.title = [NSString stringWithFormat:@"第%d个导航项",count];
    [navigationItem setLeftBarButtonItem:leftButton];
    navigationItem.rightBarButtonItem = rightButton;
    return navigationItem;
}
- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

@end

上方程序中，push，pop方法负责用于控制导航条中的 UINavigationItem的出栈进栈

效果图：

进出栈设置的动画，所以进出栈会有向左或者向右滑动的效果