UITabBar使用详解

UITabBarController使用得非常广泛，说说它的核心，UITabBar的使用。

建一个工程，创建4个UIViewController用来作切换的视图控制器，为了方便，就在AppDelegate.m文件里面写代码，如下：

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];

    FirstViewController *fvc = [[FirstViewController alloc]init];
    UINavigationController *fNav = [[UINavigationController alloc]initWithRootViewController:fvc];
    
    SecondViewController *svc = [[SecondViewController alloc]init];
    UINavigationController *sNav = [[UINavigationController alloc]initWithRootViewController:svc];
    
    ThirdViewController *tvc = [[ThirdViewController alloc]init];
    UINavigationController *tNav = [[UINavigationController alloc]initWithRootViewController:tvc];
    
    FourthViewController *fourVc = [[FourthViewController alloc]init];
    UINavigationController *fourNav = [[UINavigationController alloc]initWithRootViewController:fourVc];
    
    UITabBarController *tab = [[UITabBarController alloc]init];
    tab.viewControllers = @[fNav,sNav,tNav,fourNav];
    self.window.rootViewController = tab;
    self.window.backgroundColor = [UIColor whiteColor];
    [self.window makeKeyAndVisible];
    return YES;
}

FirstViewController、SecondViewController、ThirdViewController、FourthViewController是UITabBarController的4个标签控制器，为了区别，设置self.view.backgroundColor为不同颜色，创建UITabBarController对象tab并设置好viewControllers属性，设置tab为window的rootViewController。

UITabBarController *tab = [[UITabBarController alloc]init];
    tab.viewControllers = @[fNav,sNav,tNav,fourNav];
    self.window.rootViewController = tab;

运行看看：

这时没有设置标签的icon和title，所以tabBar上面什么都没有，但是还是可以点击切换。改变一下TabBar的背景色，设置为黑色：

tab.tabBar.barTintColor = [UIColor blackColor];

效果如下：

下面为添加4个icon和文字，icon和文字是设置在UITabBarItem对象上的，先看看系统自带的图标效果，系统图标和文字是统一的，不用再单独添加文字，修改代码如下：

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    
    FirstViewController *fvc = [[FirstViewController alloc]init];
    UINavigationController *fNav = [[UINavigationController alloc]initWithRootViewController:fvc];
    //设置系统tabBarItem1
    fvc.tabBarItem = [[UITabBarItem alloc]initWithTabBarSystemItem:UITabBarSystemItemFavorites tag:0];
    
    SecondViewController *svc = [[SecondViewController alloc]init];
    UINavigationController *sNav = [[UINavigationController alloc]initWithRootViewController:svc];
    //设置系统tabBarItem2
    svc.tabBarItem = [[UITabBarItem alloc]initWithTabBarSystemItem:UITabBarSystemItemContacts tag:1];
    
    ThirdViewController *tvc = [[ThirdViewController alloc]init];
    UINavigationController *tNav = [[UINavigationController alloc]initWithRootViewController:tvc];
    //设置系统tabBarItem3
    tvc.tabBarItem = [[UITabBarItem alloc]initWithTabBarSystemItem:UITabBarSystemItemBookmarks tag:2];
    
    FourthViewController *fourVc = [[FourthViewController alloc]init];
    UINavigationController *fourNav = [[UINavigationController alloc]initWithRootViewController:fourVc];
    //设置系统tabBarItem4
    fourVc.tabBarItem = [[UITabBarItem alloc]initWithTabBarSystemItem:UITabBarSystemItemRecents tag:3];
    
    UITabBarController *tab = [[UITabBarController alloc]init];
    tab.viewControllers = @[fNav,sNav,tNav,fourNav];
    tab.tabBar.barTintColor = [UIColor blackColor];
    self.window.rootViewController = tab;
    self.window.backgroundColor = [UIColor whiteColor];
    [self.window makeKeyAndVisible];
    return YES;
}

效果如下：

系统默认的选中颜色是蓝色，设置tintColor属性，改变选中标签的颜色：

//设置icon的颜色
    tab.tabBar.tintColor = [UIColor redColor];

效果如下：

使用自定义图片来设置tabBar，使用initWithTitle：image：tag：方法，苹果官方文档说明图片的大小为30*30，Retina屏为60*60（stackoverflow上有大神指出，UITabBarItem图标的最佳尺寸是48*32）：

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    
    FirstViewController *fvc = [[FirstViewController alloc]init];
    UINavigationController *fNav = [[UINavigationController alloc]initWithRootViewController:fvc];
    //设置自定义图片 tabBarItem1
    fvc.tabBarItem = [[UITabBarItem alloc]initWithTitle:@"首页" image:[UIImage imageNamed:@"home"] tag:0];
    
    SecondViewController *svc = [[SecondViewController alloc]init];
    UINavigationController *sNav = [[UINavigationController alloc]initWithRootViewController:svc];
    //设置自定义图片 tabBarItem2
    svc.tabBarItem = [[UITabBarItem alloc]initWithTitle:@"消息" image:[UIImage imageNamed:@"message"] tag:1];
    
    ThirdViewController *tvc = [[ThirdViewController alloc]init];
    UINavigationController *tNav = [[UINavigationController alloc]initWithRootViewController:tvc];
    //设置自定义图片 tabBarItem3
    tvc.tabBarItem = [[UITabBarItem alloc]initWithTitle:@"购物车" image:[UIImage imageNamed:@"car"] tag:2];
    
    FourthViewController *fourVc = [[FourthViewController alloc]init];
    UINavigationController *fourNav = [[UINavigationController alloc]initWithRootViewController:fourVc];
    //设置自定义图片 tabBarItem4
    fourVc.tabBarItem = [[UITabBarItem alloc]initWithTitle:@"个人中心" image:[UIImage imageNamed:@"customer"] tag:3];
    
    UITabBarController *tab = [[UITabBarController alloc]init];
    tab.viewControllers = @[fNav,sNav,tNav,fourNav];
    tab.tabBar.barTintColor = [UIColor blackColor];
    //设置icon的颜色
    tab.tabBar.tintColor = [UIColor redColor];
    self.window.rootViewController = tab;
    self.window.backgroundColor = [UIColor whiteColor];
    [self.window makeKeyAndVisible];
    return YES;
}

效果如下：

UITabBarItem有一个selectedImage属性，很明显这个是选中时显示的icon，这里需要说明一下，这默认情况下，选中时的icon只会改变颜色（由tintColor设置），如果需要改变选中时的图片，就要设置selectedImage属性，可以单独设置也可以用初始化方法设置