UITabBarController底层实现

1.首先要了解:任何控制器,都能添加子控制器

     UIViewController里面有一个方法:

    - (void)addChildViewController:(UIViewController *)childController;

     所有的控制器都继承自UIViewController

2.UITabBarController内部结构和管理原则

     2.1 内部结构

          UITabBarController内部有两个子控件,一个存放自控制器view的view    一个TabBar条

     2.2 管理原则

          TabBar上有多少个按钮,由UITabBarController自控制器的个数决定

          按钮的内容有对应的子控制器决定

     2.3 怎么切换?

          点击按钮,就找到按钮对应的控制器,记录当前的按钮

          先移除上一个控制器的view,再把当前按钮对应的+控制器的view添加上去

3.自定义UITabBarController的步骤

     3.1 搭建界面(1.存放自控制器的view(占位view) 2.UITabBar)

     3.2 添加子控制器,把按钮的内容保存到子控制器

     3.3 遍历子控制器,给UITabBar添加按钮(给按钮绑定tag 以便区分)

     3.4 监听按钮点击,先移除上一个按钮对应的控制器的view,并记录当前的按钮

     3.5 监听按钮点击,把按钮对应的子控制器的View 添加到占位视图里面

 @interface ViewController ()
 @property (weak, nonatomic) IBOutlet UIView *containerView;
 @property (nonatomic, weak) UIButton *selectedButton;
 @property (weak, nonatomic) IBOutlet UIView *tabBar;
 @end

 @implementation ViewController

 - (void)viewDidLoad {
     [super viewDidLoad];

     // 添加子控制器
     UIViewController *vc = [[UIViewController alloc] init];
     vc.title = @"全部";
     vc.view.backgroundColor = [UIColor orangeColor];
     [self addChildViewController:vc];

     UIViewController *vc1 = [[UIViewController alloc] init];
     vc1.title = @"视频";
     vc1.view.backgroundColor = [UIColor brownColor];
     [self addChildViewController:vc1];

     UIViewController *vc2 = [[UIViewController alloc] init];
     vc2.title = @"图片";
     vc2.view.backgroundColor = [UIColor greenColor];
     [self addChildViewController:vc2];

     // 添加按钮
     [self setupTitleButton];
 }
 #pragma mark - 添加按钮
 - (void)setupTitleButton
 {
     NSInteger count = self.childViewControllers.count;
     CGFloat screenW = [UIScreen mainScreen].bounds.size.width;
     CGFloat btnW = screenW / count;
     CGFloat btnH = self.tabBar.bounds.size.height;
     CGFloat btnX = ;
     CGFloat btnY = ;
     for (int i = ; i < count; i++) {
         UIButton *btn = [UIButton buttonWithType:UIButtonTypeCustom];
         btn.tag = i;
         [btn setTitleColor:[UIColor blackColor] forState:UIControlStateNormal];
         [btn setTitleColor:[UIColor redColor] forState:UIControlStateSelected];
         UIViewController *vc = self.childViewControllers[i];
         [btn setTitle:vc.title forState:UIControlStateNormal];
         btnX = i * btnW;
         btn.frame = CGRectMake(btnX, btnY, btnW, btnH);
         [self.tabBar addSubview:btn];

         // 监听按钮点击
         [btn addTarget:self action:@selector(btnClick:) forControlEvents:UIControlEventTouchUpInside];
         if (i == ) {
             [self btnClick:btn];
         }
     }
 }

 - (void)btnClick:(UIButton *)button
 {
     NSInteger i = button.tag;
     _selectedButton.selected = NO;
     button.selected = YES;
     _selectedButton = button;
     // 获取子控制器
     UIViewController *vc = self.childViewControllers[i];
     // 移除之前的控制器View
     [self.containerView.subviews makeObjectsPerformSelector:@selector(removeFromSuperview)];
     // 添加当前控制器的view
     [self.containerView addSubview:vc.view];
 }