在IOS开发的过程中我们经常会遇到一些紧贴tabbar有工具条之类的页面，比如说购买、支付等页面，往往这些页面有时候在栈底显示（页面有tabbar），有时不在（页面没有tabbar）。比如：

这种页面对于常规的做法是有tabbar的时候设置一套约束，没有tabbar的时候更新一下约束。但是苹果提过了一个bottomLayoutGuide可以让我们更优雅的处理这类问题。
代码如下：

_bottomView = [UIView new];
    _bottomView.backgroundColor = [UIColor yellowColor];
    [self.view addSubview:_bottomView];
    [_bottomView mas_makeConstraints:^(MASConstraintMaker *make) {
        make.height.equalTo(@40);
        make.left.and.right.equalTo(self.view);
        make.bottom.equalTo(self.mas_bottomLayoutGuide);
    }];

搭配Masonry，使用Masonry提供的mas_bottomLayoutGuide仅需一行我们就可以实现这样的效果。

同样来说这种效果对于navigationBar也适用——topLayoutGuide。对应的Masonry使用方法是mas_topLayoutGuide。
完整代码（代码量太少就不给完整的链接了）：

#import "ViewController.h"
#import "Masonry.h"
@interface ViewController ()
@property (strong, nonatomic) UIView *topView;
@property (strong, nonatomic) UIView *bottomView;
@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    UIButton *btn = [UIButton buttonWithType:UIButtonTypeCustom];
    btn.frame = CGRectMake(0, 164, 80, 50);
    [btn setTitle:@"top" forState:UIControlStateNormal];
    btn.backgroundColor = [UIColor redColor];
    [btn addTarget:self action:@selector(topClick) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:btn];

    UIButton *btn1 = [UIButton buttonWithType:UIButtonTypeCustom];
    btn1.backgroundColor = [UIColor yellowColor];
    btn1.frame = CGRectMake(0, 264, 80, 50);
    [btn1 setTitle:@"bottom" forState:UIControlStateNormal];
    [btn1 setTitleColor:[UIColor blackColor] forState:UIControlStateNormal];
    [btn1 addTarget:self action:@selector(bottomClick) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:btn1];
    [self initView];
}

- (void)initView {
    _topView = [UIView new];
    _topView.backgroundColor = [UIColor greenColor];
    [self.view addSubview:_topView];
    [_topView mas_makeConstraints:^(MASConstraintMaker *make) {
        make.height.equalTo(@40);
        make.left.and.right.equalTo(self.view);

        make.top.equalTo(self.mas_topLayoutGuide);

    }];

    _bottomView = [UIView new];
    _bottomView.backgroundColor = [UIColor yellowColor];
    [self.view addSubview:_bottomView];
    [_bottomView mas_makeConstraints:^(MASConstraintMaker *make) {
        make.height.equalTo(@40);
        make.left.and.right.equalTo(self.view);
        make.bottom.equalTo(self.mas_bottomLayoutGuide);
    }];
}
- (void)topClick{

    [self.navigationController setNavigationBarHidden:!self.navigationController.navigationBarHidden animated:NO];
//    [self updateViewConstraints];
}
- (void)bottomClick{

    [self.navigationController setToolbarHidden:!self.navigationController.toolbarHidden animated:NO];
    // 手动触发updateViewConstraints
//    [self updateViewConstraints];
}
- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

@end