请问你是想自定义 tabbar 的高度还是想调整 content view 的高度？ 你可以使用下面的方法来打印出 UITabBarController 的 View 的子视图信息来查看视图层级的布局:

- (void)viewDidAppear:(BOOL)animated
{
    [super viewDidAppear:animated];
    [self printViewHierarchy:self.tabBarController.view];
}

- (void)printViewHierarchy:(UIView *)superView
{
    static uint level = 0;
    for(uint i = 0; i < level; i++){
        printf("\t");
    }

    const char *className = NSStringFromClass([superView class]).UTF8String;
    const char *frame = NSStringFromCGRect(superView.frame).UTF8String;
    printf("%s:%s\n", className, frame);

    ++level;
    for(UIView *view in superView.subviews){
        [self printViewHierarchy:view];
    }
    --level;
}

结果如下:

UILayoutContainerView:{{0, 0}, {320, 480}}
    UITransitionView:{{0, 0}, {320, 480}}
        UIViewControllerWrapperView:{{0, 0}, {320, 480}}
            UIView:{{0, 0}, {320, 480}}
    UITabBar:{{0, 431}, {320, 49}}
        _UITabBarBackgroundView:{{0, 0}, {320, 49}}
            _UIBackdropView:{{0, 0}, {320, 49}}
                _UIBackdropEffectView:{{0, 0}, {320, 49}}
                UIView:{{0, 0}, {320, 49}}
        UITabBarButton:{{2, 1}, {156, 48}}
            UITabBarSwappableImageView:{{54, 2}, {48, 32}}
            UITabBarButtonLabel:{{68, 35}, {21, 12}}
        UITabBarButton:{{162, 1}, {156, 48}}
            UITabBarSwappableImageView:{{54, 2}, {48, 32}}
            UITabBarButtonLabel:{{60, 35}, {36, 12}}
        UIImageView:{{0, -0.5}, {320, 0.5}}