UINavigationController切换视图的简单使用

UINavigationController通过栈的方式来管理视图，通过push将视图压入栈，pop将视图推出栈。

下面通过简单的示例说明

AppDelegate.m

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

    self.window = [[UIWindow alloc] initWithFrame:[UIScreen mainScreen].bounds];

    ViewController *vc = [[ViewController alloc] init];

    UINavigationController *vcNav = [[UINavigationController alloc] initWithRootViewController:vc];
    self.window.rootViewController = vcNav;

    [self.window makeKeyAndVisible];

    return YES;
}

ViewController.m

- (void)viewDidLoad
{
    [super viewDidLoad];

    self.view.backgroundColor = [UIColor whiteColor];
    /*

     导航标题的设置可通过三种方式，且显示优先级如下：
     self.navigationItem.titleView > self.navigationItem.title > self.title

     例如这里我们同时使用前两种方式，则默认显示titleView的内容

     */
    //导航标题
    UILabel *labelView = [[UILabel alloc] initWithFrame:CGRectMake(0, 0, 500, 30)];
    labelView.text = @"我是根视图";
    labelView.textAlignment = NSTextAlignmentCenter;
    self.navigationItem.titleView = labelView;
    self.navigationItem.title = @"我不是根视图";

    //左边导航按钮
    UIButton *leftButton = [[UIButton alloc] initWithFrame:CGRectMake(0, 0, 50, 30)];
    [leftButton setTitle:@"按钮" forState:UIControlStateNormal];
    [leftButton setTitleColor:[UIColor blackColor] forState:UIControlStateNormal];
    UIBarButtonItem *leftItem = [[UIBarButtonItem alloc] initWithCustomView:leftButton];
    self.navigationItem.leftBarButtonItem = leftItem;
    //右边导航按钮
    UIButton *rightButton = [[UIButton alloc] initWithFrame:CGRectMake(0, 0, 50, 30)];
    [rightButton setTitle:@"跳转" forState:UIControlStateNormal];
    [rightButton setTitleColor:[UIColor blackColor] forState:UIControlStateNormal];
    [rightButton addTarget:self action:@selector(clickedRightButton) forControlEvents:UIControlEventTouchUpInside];
    UIBarButtonItem *rightItem = [[UIBarButtonItem alloc] initWithCustomView:rightButton];
    self.navigationItem.rightBarButtonItem = rightItem;

    /*

     backBarButtonItem的使用
     如果AController push到 BController，那么有以下几种情况
     1：B设置了leftBarButtonItem,则优先显示B的leftBarButtonItem
     2：B没有设置leftBarButtonItem,A设置了backBarButtonItem,则显示A设置的backBarButtonItem
     3：B没有设置leftBarButtonItem,A没有设置backBarButtonItem,则系统会拿到A的title显示一个返回按钮
     所以B左边按钮的显示优先级如下：
     B的leftBarButtonItem > A的backBarButtonItem > 系统默认的返回按钮
     大家可以先注释掉标号①的那行代码，然后同时注释掉标号①②的代码，来试验一下。

     这里注意，backBarButtonItem只能自定义title和image,如下注释掉的方法是无效的。

     */
    //返回按钮
    //    UIButton *backButton = [[UIButton alloc] initWithFrame:CGRectMake(0, 0, 50, 30)];
    //    [backButton setTitle:@"返回" forState:UIControlStateNormal];
    //    [backButton setTitleColor:[UIColor blackColor] forState:UIControlStateNormal];
    //    UIBarButtonItem *backItem = [[UIBarButtonItem alloc] initWithCustomView:backButton];
    UIBarButtonItem *backItem = [[UIBarButtonItem alloc] initWithTitle:@"我是返回" style:UIBarButtonItemStylePlain target:self action:nil];
    self.navigationItem.backBarButtonItem = backItem;                               //②

    UILabel *tipsLabel = [[UILabel alloc] initWithFrame:CGRectMake(20, 300, self.view.frame.size.width-40, 20)];
    tipsLabel.text = @"我是根视图";
    tipsLabel.textAlignment = NSTextAlignmentCenter;
    tipsLabel.textColor = [UIColor redColor];
    [self.view addSubview:tipsLabel];

}
- (void)clickedRightButton
{
    ChildViewController *childVC = [[ChildViewController alloc] init];
    [self.navigationController pushViewController:childVC animated:YES];
}

ChildViewController.m

- (void)viewDidLoad
{
    [super viewDidLoad];

    self.view.backgroundColor = [UIColor lightGrayColor];
    //导航标题
    UILabel *labelView = [[UILabel alloc] initWithFrame:CGRectMake(0, 0, 10, 30)];
    labelView.text = @"我是子视图";
    labelView.textAlignment = NSTextAlignmentCenter;
    self.navigationItem.titleView = labelView;
    //左边导航按钮
    UIButton *leftButton = [[UIButton alloc] initWithFrame:CGRectMake(0, 0, 50, 30)];
    [leftButton setTitle:@"返回" forState:UIControlStateNormal];
    [leftButton setTitleColor:[UIColor blackColor] forState:UIControlStateNormal];
    [leftButton addTarget:self action:@selector(clickedLeftButton) forControlEvents:UIControlEventTouchUpInside];
    UIBarButtonItem *leftItem = [[UIBarButtonItem alloc] initWithCustomView:leftButton];
    self.navigationItem.leftBarButtonItem = leftItem;                       //①
    //右边导航按钮
    UIButton *rightButton = [[UIButton alloc] initWithFrame:CGRectMake(0, 0, 50, 30)];
    [rightButton setTitle:@"按钮" forState:UIControlStateNormal];
    [rightButton setTitleColor:[UIColor blackColor] forState:UIControlStateNormal];
    UIBarButtonItem *rightItem = [[UIBarButtonItem alloc] initWithCustomView:rightButton];
    self.navigationItem.rightBarButtonItem = rightItem;

    UILabel *tipsLabel = [[UILabel alloc] initWithFrame:CGRectMake(20, 300, self.view.frame.size.width-40, 20)];
    tipsLabel.text = @"我是子视图";
    tipsLabel.textAlignment = NSTextAlignmentCenter;
    tipsLabel.textColor = [UIColor blueColor];
    [self.view addSubview:tipsLabel];
}

- (void)clickedLeftButton
{
    [self.navigationController popViewControllerAnimated:YES];
}

再说明下titleView的宽度问题

根视图中将labelView设置了500的宽度，而子视图中将labelView设置了10的宽度，但是显示效果是一样的，下面我们详细对比下这两种有什么不同。

我们可以看到，leftBarButtonItem距离左边距有16个像素，和titleView至少有6像素的距离；rightBarButtonItem同理。

所以我们假设屏幕宽度为ScreenW，标题文字的实际宽度为labelW，左边按钮宽度为leftW，右边按钮宽度为rightW，titleView的最终宽度为titleViewW。

①如果titleViewW < labelW，则titleViewW 为 labelW；

②如果labelW < titleViewW < ScreenW-16*2-6*2-leftW-rightW，则titleViewW 为 titleViewW；

③如果titleViewW > ScreenW-16*2-6*2-leftW-rightW，则titleViewW 为 ScreenW-16*2-6*2-leftW-rightW。

实际开发中可能会遇到标题过长，需要使用省略号“…”显示，如下图所示

此时让标题居中的办法就是将leftW和rightW设置为相等即可；

如果只有左边返回按钮，而没有右边按钮，则放置一个空视图占位，即可方便实现标题居中。