自定义tabBarItem，仍是使用系统的tabBar

- (void)viewDidLoad {
    [super viewDidLoad];
    
    // 使用系统自带的tabBar注意这两个函数的先后顺序
    [self createViewControllers];
    [self createMyTabBarItem];

}

- (void)createMyTabBarItem {
    // 移除系统自带的tabBarItem
    for (UIView * view  in self.tabBar.subviews) {
        [view removeFromSuperview];
    }
    //    // PUSH到下一个界面的时候，BottomBar自动隐藏
    //    self.hidesBottomBarWhenPushed = YES;
    
    NSArray * imgs = @[@"movie",@"cinema",@"me"];
    NSArray * preImgs = @[@"movie_press",@"cinema_press",@"me_press"];
    // 各个item之间的间距
    CGFloat space = (__kScreenWidth-33*3)/4;
    for (int i=0; i<imgs.count; i++) {
        UIButton * btn = [UIButton buttonWithType:UIButtonTypeCustom];
        btn.frame = CGRectMake(space+(33+space)*i, 10, 33, 33);
        UIImage * image = [UIImage imageNamed:imgs[i]];
        image = [image imageWithRenderingMode:UIImageRenderingModeAlwaysOriginal];
        [btn setBackgroundImage:image forState:UIControlStateNormal];
        UIImage * pressImg = [UIImage imageNamed:preImgs[i]];
        pressImg = [pressImg imageWithRenderingMode:UIImageRenderingModeAlwaysOriginal];
        [btn setBackgroundImage:pressImg forState:UIControlStateSelected];
        [btn addTarget:self action:@selector(btnClick:) forControlEvents:UIControlEventTouchUpInside];
        btn.tag = 100+i;
        [self.tabBar addSubview:btn];
        // 默认启动显示是第一个界面
        if (i==0) {
            btn.selected = YES;
        }
    }
}

- (void)btnClick:(UIButton *)sender {
    // 设置视图切换
    NSInteger index = sender.tag-100;
    self.selectedIndex = index;

    for (UIView * view in self.tabBar.subviews) {
        // 要判断view的类型
        if ([view isKindOfClass:[UIButton class]]) {
            UIButton * btn = (UIButton *)view;
            if (btn.tag == sender.tag) {
                btn.selected = YES;
            } else {
                btn.selected = NO;
            }
        }
    }
    /*
     self.tabBar.subviews.count = 5;
     self.tabBar.subviews:
     (
     "<_UITabBarBackgroundView: 0x7fc513ff48c0; frame = (0 0; 375 49); autoresize = W; userInteractionEnabled = NO; layer = <CALayer: 0x7fc513ff4c40>>",
     "<UIButton: 0x7fc513e238e0; frame = (56.25 0; 50 49); opaque = NO; tag = 100; layer = <CALayer: 0x7fc513e23d40>>",
     "<UIButton: 0x7fc513fda4b0; frame = (162.5 0; 50 49); opaque = NO; tag = 101; layer = <CALayer: 0x7fc513fda6d0>>",
     "<UIButton: 0x7fc513fe4520; frame = (268.75 0; 50 49); opaque = NO; tag = 102; layer = <CALayer: 0x7fc513fe1920>>",
     "<UIImageView: 0x7fc513ff5ab0; frame = (0 -0.5; 375 0.5); autoresize = W; userInteractionEnabled = NO; layer = <CALayer: 0x7fc513ff5720>>"
     )
     */
}

- (void)createViewControllers {
    NSMutableArray * viewControllers = [[NSMutableArray alloc] init];
//    NSArray * classNames = @[@"MovieViewController",@"CinemaViewController",@"SettingViewController"];
//    for (NSInteger i=0; i<classNames.count; i++) {
//        //将字符串表示的类名转换为类（对象）
//        Class class = NSClassFromString(classNames[i]);
//        BaseViewController * bVC = [[class alloc] init];
//        
//        UINavigationController * nav = [[UINavigationController alloc] initWithRootViewController:bVC];
//        [viewControllers addObject:nav];
//
//    }
    
    MovieViewController * MVC = [[MovieViewController alloc] init];
    [MVC becomeObserve];
    UINavigationController * Mnav = [[UINavigationController alloc] initWithRootViewController:MVC];
    [viewControllers addObject:Mnav];
    
    CinemaViewController * CVC = [[CinemaViewController alloc] init];
    [CVC becomeObserve];
    UINavigationController * Nnav = [[UINavigationController alloc] initWithRootViewController:CVC];
    [viewControllers addObject:Nnav];
    
    SettingViewController * SVC = [[SettingViewController alloc] init];
    UINavigationController * Snav = [[UINavigationController alloc] initWithRootViewController:SVC];
    [viewControllers addObject:Snav];
    
    self.viewControllers = viewControllers;

}