基本组件的使用——UINavigationController

做用：在多个ViewController中切换。UINavigationController内部以栈的形式维护一组ViewController，

所以，当导航进入一个新视图的时候，会以push的形式将该ViewController压入栈，当须要返回上一层视图的时候则以pop的形式将当前的ViewController弹出栈顶。

先来看一下咱们要实现的效果：

而后是代码：

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {

    //建立第一个视图
    self.firstViewController = [[UIViewController alloc] init];
    self.firstViewController.view.backgroundColor = [UIColor whiteColor];
    self.firstViewController.title = @"first view";
    
    //在主视图中建立按钮
    UIButton *firstBtn = [self createButton:@"to second" target:@selector(push)];
    
    //将按钮添加到视图中
    [self.firstViewController.view addSubview:firstBtn];
    
    self.navController = [[UINavigationController alloc]
                          initWithRootViewController:self.firstViewController];
    
    NSLog(@"%@", self.navController.viewControllers);
    NSLog(@"%@", self.firstViewController);
    
    //建立第二个视图
    self.secondViewController = [[UIViewController alloc] init];
    self.secondViewController.view.backgroundColor = [UIColor whiteColor];
    self.secondViewController.title = @"second view";
    
    //在第二个视图中建立按钮
    UIButton *secondBtn = [self createButton:@"to first" target:@selector(pop)];
    
    //将按钮添加到第二个视图
    [self.secondViewController.view addSubview:secondBtn];
    
    self.window.rootViewController = self.navController;
    
    return YES;
}

#pragma mark - 自定义方法
- (void)push
{
    [self.navController pushViewController:self.secondViewController animated:YES];
}

- (void)pop
{
    [self.navController popViewControllerAnimated:YES];
}

- (UIButton *)createButton:(NSString *)title target:(SEL)selector
{
    CGRect btnFrame = CGRectMake(100, 100, 100, 25);
    UIButton *button = [UIButton buttonWithType:UIButtonTypeSystem];
    [button setFrame:btnFrame];
    [button setTitle:title forState:UIControlStateNormal];
    [button setBackgroundColor:[UIColor lightGrayColor]];
    [button setTitleColor:[UIColor blackColor]
                   forState:UIControlStateNormal];
    [button addTarget:self action:selector
       forControlEvents:UIControlEventTouchUpInside];
    
    return button;
}

整个过程都在- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions方法中完成。

如今咱们来分析一下navigationcontroller栈中的状况，当初始化完成的时候是这样的：

一切准备就绪以后咱们就能够点击to second按钮，这个时候SecondViewController会被压入栈顶，亦便是切换到SecondViewController控制的视图：

一样地，当咱们在SecondViewController返回的时候popViewControllerAnimated:方法会被执行，结果是SecondViewController会被弹出栈顶，只剩下FirstViewController：

popViewControllerAnimated:方法老是将栈顶的ViewController弹出，所以它不须要接受ViewController做为参数。

明白了这个原理，UINavigationController的使用其实很简单。